tag:blogger.com,1999:blog-23996264146037815132024-03-17T20:00:27.898-07:00Jon Davies Severe Weather NotesJon's blog: Comments and observations about recent tornado/severe weather cases and issues.Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.comBlogger156125tag:blogger.com,1999:blog-2399626414603781513.post-70537103677778426892021-12-14T13:10:00.040-08:002021-12-17T06:45:08.684-08:00Tornadoes, Warehouses, and Factories - Can these businesses do better to keep workers safe?<p><i>(<b>This is an essay/opinion piece my wife <u>Shawna wrote</u> and wanted to share here on my blog after last Friday's catastrophic and stunning tornado event in Kentucky, Illinois, Arkansas, Tennessee and Missouri.</b> - Jon Davies) </i><span style="font-size: medium;"> </span></p><p><span style="font-size: medium;">(You can help Western Kentucky tornado victims by donating <a href="https://secure.kentucky.gov/formservices/Finance/WKYRelief" target="_blank">here</a>.) </span></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEh4l6PL2Gu1MFsa74aMLEo1oszmzcxgWrNb7zdcTD7MKvxntszLAsQDVxvsVVGinAAupS1m8RSnMObHA6NCBUYRwyHREmsdSB-UK208s2Ga6ICjQssBdwE47JVu1pxPZTauA8Qm4qVU2K0RF4sxFE0fi2aK5QlJ57JizD-QCm2PqaFmDmGTkWNvj2HWsg=s742" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="565" data-original-width="742" height="488" src="https://blogger.googleusercontent.com/img/a/AVvXsEh4l6PL2Gu1MFsa74aMLEo1oszmzcxgWrNb7zdcTD7MKvxntszLAsQDVxvsVVGinAAupS1m8RSnMObHA6NCBUYRwyHREmsdSB-UK208s2Ga6ICjQssBdwE47JVu1pxPZTauA8Qm4qVU2K0RF4sxFE0fi2aK5QlJ57JizD-QCm2PqaFmDmGTkWNvj2HWsg=w640-h488" width="640" /></a></div><br /><i><br /></i><p></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>I was heart-broken watching the devastating tornado outbreak unfold last Friday night (December 10-11) in the central Mississippi River Valley area . It was the most catastrophic U.S. tornado episode since the 2011 Joplin tornado and the 2011 Dixie Super Outbreak, and the deadliest tornado outbreak ever recorded in the U.S. during the month of December!</p><p>Kentucky bore the brunt of it, with at least 74 deaths in the state confirmed so far (the death toll may rise as there are still people unaccounted for), and additional tornado deaths in Illinois, Arkansas, Tennessee, and Missouri. This outbreak included a tornado that would have had the longest track ever recorded (> 220 miles across parts of four states) except for a short break at one point in its path. This tornado killed at least 57 people, and while officially rated EF4 intensity at this time, there were areas of damage that could conceivably suggest EF5 wind speeds. Regardless, last Friday was a truly historic yet dark and sad day.</p><p>From a safety viewpoint in the future, is there anything we can learn from this event?</p><p>I want to focus on a couple locations: First, the Amazon facility that was struck by a narrow but strong tornado (EF3) near Edwardsville, Illinois, killing six people (see photos below): </p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEgehtHF8vPfjVUYMC2wypNmhHWjnkbpwd2h2wwimgsAqBypT8yI8okVFXO9ES75qSQUO45RmcnpNGZbb8cKxjReSLpipBXz2LIHdj7GwQeZXqo8hmUdOfnIK3gGPZsFdtdABXD3Nde83EcPdoL6RltwdzLlMC9uZZ8AkXOasm2AVPfP8BL9rQ9ocS0Tzw=s448" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="354" data-original-width="448" height="316" src="https://blogger.googleusercontent.com/img/a/AVvXsEgehtHF8vPfjVUYMC2wypNmhHWjnkbpwd2h2wwimgsAqBypT8yI8okVFXO9ES75qSQUO45RmcnpNGZbb8cKxjReSLpipBXz2LIHdj7GwQeZXqo8hmUdOfnIK3gGPZsFdtdABXD3Nde83EcPdoL6RltwdzLlMC9uZZ8AkXOasm2AVPfP8BL9rQ9ocS0Tzw=w400-h316" width="400" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEhB9yuDlWepeZDLAI1isA3ZdyOP5wiDzni8BBr1dxlhPtflIFFkoZlBInM2xPsEI0hzRO5IqlGY4qhgBaJL6Q2iJ2UzjIPLXOadYW_p3JdwoILqywCVp_EExrRB4NkLQ21JZYA-MYFNJL4Xtekat-psDX-lY6uqAOiQ-PK8YiMj79i0RE1G32LJO6x_qw=s885" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="712" data-original-width="885" height="321" src="https://blogger.googleusercontent.com/img/a/AVvXsEhB9yuDlWepeZDLAI1isA3ZdyOP5wiDzni8BBr1dxlhPtflIFFkoZlBInM2xPsEI0hzRO5IqlGY4qhgBaJL6Q2iJ2UzjIPLXOadYW_p3JdwoILqywCVp_EExrRB4NkLQ21JZYA-MYFNJL4Xtekat-psDX-lY6uqAOiQ-PK8YiMj79i0RE1G32LJO6x_qw=w400-h321" width="400" /></a></div><p>I'll also discuss the candle factory in Mayfield, Kentucky where eight people died when it was completely destroyed by the large long-track violent tornado (at least EF4 intensity) that tore through western Kentucky (see photos below):</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEjHjoPMT650uGwrLpEAiu49IBYIy6BySsCoLUqM4J2z_K93KK7Z1eFnfq_D0QkbeTKcnkaOqFR3TOFHWKsQROiJrQHcsnee1SZpmx-YjUyyTKNoDvznoh0Cqg8C04092y-edHcQMPZ2iMI7XTF5KcLEuG-1EBMfPPKvJ2XiMelkVwsljIV6YWUs7WDeaA=s411" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="352" data-original-width="411" height="343" src="https://blogger.googleusercontent.com/img/a/AVvXsEjHjoPMT650uGwrLpEAiu49IBYIy6BySsCoLUqM4J2z_K93KK7Z1eFnfq_D0QkbeTKcnkaOqFR3TOFHWKsQROiJrQHcsnee1SZpmx-YjUyyTKNoDvznoh0Cqg8C04092y-edHcQMPZ2iMI7XTF5KcLEuG-1EBMfPPKvJ2XiMelkVwsljIV6YWUs7WDeaA=w400-h343" width="400" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEj1yGt_H6SPHv0GyN0hH9nSCZbFef7ZtVu7WP31Z6s3JvG_EhBu-JGYsVv6CIENslN-hY8L3XdjWLD4ENewWvF_dhMmxBjK-VsAD07mk-mvOUeqL6dv1fvbAYrn-yLHawOWjb_m5058zClLLTr1TrlyoSZ7GpL5Eut26Q-P2O_hQY93hYiWJxng5sRXHg=s945" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="660" data-original-width="945" height="279" src="https://blogger.googleusercontent.com/img/a/AVvXsEj1yGt_H6SPHv0GyN0hH9nSCZbFef7ZtVu7WP31Z6s3JvG_EhBu-JGYsVv6CIENslN-hY8L3XdjWLD4ENewWvF_dhMmxBjK-VsAD07mk-mvOUeqL6dv1fvbAYrn-yLHawOWjb_m5058zClLLTr1TrlyoSZ7GpL5Eut26Q-P2O_hQY93hYiWJxng5sRXHg=w400-h279" width="400" /></a></div><p>Both facilities had ample warning via NWS warnings, around 20 minutes lead time in each case. The Amazon facility in Illinois, which is now being investigated by the federal government via OSHA regarding structural issues (see <a href="https://abcnews.go.com/Business/dead-amazon-facility-tornado-pummels-illinois/story?id=81721932" target="_blank">here</a>), had no below-ground area or solid concrete floor-level safe rooms for the 40+ employees working on Friday evening. Similarly, the Mayfield Consumer Products candle factory apparently had no basement or above-ground concrete shelters when the half-mile wide violent tornado struck, although employees were told to go to hallways and bathrooms. Given the typical low-end construction quality of many such warehouse structures (most large industrial buildings are not designed to withstand extreme winds, with roofs often blowing off and adjacent walls collapsing), the lack of true shelters and safe rooms in these cases probably contributed greatly to the deaths. That said, it was very fortunate that, of 140 total employees in these two cases, only 14 lost their lives. </p><p>For reference, here is a regional radar image (Edwardsville and Mayfield are marked) at about the time the Amazon facility was struck, and roughly an hour before the factory in Mayfield was hit:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEjV7r0xcrPM9GyP_TEA63R03B0eECjFz5gF1CEBaF2q0jM2yQHPhGTa23FNIXSqYNb6RQtxZV_4ztV1Zrr41uf4MWD7emTnv_1wOmBdbB8xnMZpl7tkaUvZPJkz89es4tpIn8wtf0efC2nTmX1qkKar1cj86iMfmJvpvAknVg0GFdKTN4S0dRMKDBkpkA=s577" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="577" data-original-width="448" height="400" src="https://blogger.googleusercontent.com/img/a/AVvXsEjV7r0xcrPM9GyP_TEA63R03B0eECjFz5gF1CEBaF2q0jM2yQHPhGTa23FNIXSqYNb6RQtxZV_4ztV1Zrr41uf4MWD7emTnv_1wOmBdbB8xnMZpl7tkaUvZPJkz89es4tpIn8wtf0efC2nTmX1qkKar1cj86iMfmJvpvAknVg0GFdKTN4S0dRMKDBkpkA=w310-h400" width="310" /></a></div><p>That two large industrial buildings populated with many employees were hit directly by strong and violent tornadoes on December 10 highlights sheltering and other problems in such situations. <i><b><u>It seems clear that large warehouse and factory buildings should be built or modified to have some sort of below-ground shelter or ground-level rebar-reinforced concrete safe rooms sizable enough for workers to evacuate to when tornadoes or strong winds approach</u></b></i>. Mega-profit companies like Amazon can surely afford to provide such shelters for their employees.</p><p>Other issues have surfaced in news stories about these two facilities (for example, see <a href="https://people.com/human-interest/amazon-employee-phone-policy-after-warehouse-collapse-amid-tornado/" target="_blank">here</a>). One revolves around policies that don't allow employees at work to have cell phones (a good source for weather warnings and simple-to-view radar apps). Such rules could be relaxed on days when severe weather is likely. It would also seem very prudent for companies with many employees to have <b><i><u>a designated manager to keep abreast of days when severe weather is possible, and to monitor warnings and radar</u></i></b> for storms that might directly affect their location. </p><p>==>To illustrate, on December 10, Mayfield came under a late afternoon tornado warning that sent candle factory workers to halls and bathrooms for shelter. That small storm (not shown) passed well south of Mayfield and produced no tornadoes. However, three hours later when the mega-supercell with a confirmed large long-track tornado on the ground directly approached Mayfield, there seemed to be confusion at the factory. Some workers in interviews claimed that at least one supervisor threatened to fire employees who wanted to head home for shelter with 20 minutes of lead time before the tornado hit (see <a href="https://www.nbcnews.com/news/us-news/kentucky-tornado-factory-workers-threatened-firing-left-tornado-employ-rcna8581" target="_blank">here</a>). <b><i><u>A designated manager with some basic weather training and online or cell phone access to warnings and radar could probably distinguish between the two vastly different situations, and help make urgent and intelligent decisions to keep workers safe</u></i></b>.</p><p>The last couple years have not been particularly active regarding tornado activity in the U.S. But this violent and deadly December event is a strong reminder that severe weather and tornadoes can happen any time of year, and that we all need to stay aware. <b><i><u>Have a safe place to go in severe weather, stay alert, and keep your cell phone on and handy (particularly at night) when thunderstorms are in the forecast and severe weather may be possible</u></i></b>. </p><p>On a positive note, I also want to say <b><u>how impressed I am</u></b> with the many people in media interviews who were well-informed and took the right action to protect themselves and their families as tornadoes approached last Friday. Sheltering in interior bathrooms or closets with mattresses when there was no basement was a common action among survivors interviewed. </p><p>Unfortunately, when a violent (EF4 or EF5) tornado strikes, particularly when there is no below-ground shelter or safe room, even the smartest actions may not guarantee safety. I'm paraphrasing here, but what I've heard legendary severe weather researcher Dr. Chuck Doswell say is very true: "Tornadoes are going to occur, people just happen to be in the way." </p><p>Here is a 30-minute video that a crew of storm chasers with production experience and I produced several years ago about staying safe in tornadic and severe weather. I check this video periodically, and it still stands with accurate information (<b><u>including workplace safety</u></b>): </p><p><a href="https://www.youtube.com/watch?v=FmO-e8j2ahk" target="_blank">https://www.youtube.com/watch?v=FmO-e8j2ahk</a>. </p><p>A little time spent watching this video and planning ahead may help save you and your loved ones' lives. <b><i><u>Let's all stay responsible, alert, and safe as possible</u></i></b>!</p><p>Shawna Davies 12/14/21 (with the assistance of Jon Davies) - updated 12/16/21 and 12/17/21</p><p><br /></p><p>(<b>Update</b><u> <b>12/16/21</b></u>: After writing this article, our unusual and record-breaking December severe weather hasn't let up, with the <i><u>first December tornado ever reported in Minnesota occurring last night</u></i> as a strong storm system roared through the central U.S. on Wednesday 12/15/21)</p><p>(<b style="text-decoration-line: underline;">Update</b> <b>12/17/2<u>1</u></b>: A class-action lawsuit has been filed on behalf of candle factory workers in Mayfield alleging they were told they would be fired - see discussion earlier - if they left work ahead of last Friday evening's deadly long-track tornado in western Kentucky - see <a href="https://www.cnn.com/2021/12/16/us/mayfield-candle-factory-lawsuit-tornado/index.html" target="_blank">here</a>.) </p><p>(<b><u>Update 12/17/21</u></b>: As of this morning, the tornado death toll in five states from the December 10-11, 2021 tornadoes is at least 88 dead. Western Kentucky is in particularly bad shape, and it will take some towns and citizens years to recover. You can help by donating to the <a href="https://secure.kentucky.gov/formservices/Finance/WKYRelief" target="_blank">Team Western Kentucky Tornado Relief Fund</a> established directly to help the tornado victims there.)</p><p><br /></p>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com8tag:blogger.com,1999:blog-2399626414603781513.post-68752154587207510532021-10-29T11:22:00.009-07:002021-10-30T07:58:10.088-07:00Cold-core tornado chase in northwest Missouri on October 24, 2021<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj8j7wdemiUGgtHKRFAL2K73KCbiIIUH6CyDAhCvDwzX3kMQOeHYuVk9Z-lcq4yLsOh9VrogQrgjkxPEuLQnfWwKZsSjQjh9hMPaMhdMqj_xQZSQRQfV86jhLXQc4O4SDYkrB3WGqhkA7e7/s897/102421nwMOtor_srd1_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="504" data-original-width="897" height="360" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj8j7wdemiUGgtHKRFAL2K73KCbiIIUH6CyDAhCvDwzX3kMQOeHYuVk9Z-lcq4yLsOh9VrogQrgjkxPEuLQnfWwKZsSjQjh9hMPaMhdMqj_xQZSQRQfV86jhLXQc4O4SDYkrB3WGqhkA7e7/w640-h360/102421nwMOtor_srd1_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>The past few months have been been a difficult period for my wife Shawna and me. Her mother died, a friend died, our loving cat Sadie died, and there have been both health and family issues going on. That's why I haven't posted in a while, and with some other changes for us in progress over the coming months (such as readying our house for sale and deciding where to move), blog posts here will likely continue quite few and far between.</p><p>However, we both were able to do a rare October storm chase last Sunday (October 24, 2021) close to home north of Kansas City (see image above), our first storm chase in months due to all that's been going on with us personally. This blog post presents some photos and description documenting our October 24 chase.</p><p>The satellite and surface map image below at early to mid afternoon (satellite at 2:51 pm CDT or 1951 UTC; surface data at 2:00 pm CDT or 1900 UTC) shows that the setting over northwest Missouri (MO) was a "cold-core" situation (see <a href="https://journals.ametsoc.org/view/journals/wefo/21/6/waf967_1.xml?tab_body=pdf" target="_blank">here</a>) with a surface low just west of St Joseph, and a mid-level low over southwest Iowa, with a warm front/Pacific cool front intersection near St Joseph:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhtNquD3-mxYKRxz9HNK9KvLv9RUi70lglU545TorG-0WDM7-B0dAiR-4eMSlcqgSmYQsuVxK_AaS1Ok6Mrw4TSKQYXk5pqUOtKcPB4rVWA5_wJSoLnSHoUVlyiexUqsb8CVWU0kO8aX3Ta/s607/102421sa-sfc1951_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="543" data-original-width="607" height="573" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhtNquD3-mxYKRxz9HNK9KvLv9RUi70lglU545TorG-0WDM7-B0dAiR-4eMSlcqgSmYQsuVxK_AaS1Ok6Mrw4TSKQYXk5pqUOtKcPB4rVWA5_wJSoLnSHoUVlyiexUqsb8CVWU0kO8aX3Ta/w640-h573/102421sa-sfc1951_anno.jpg" width="640" /></a></div><br /><p><br /></p><p>With a strong shortwave disturbance moving across the area (not shown, connected with the 700mb/500mb low) and associated cold air aloft located above surface temperatures in the 70's F and dew points in the 60'sF making for significant instability, we figured tornadoes were likely along the warm front just east of the surface low. Backed easterly surface winds along and north of the warm front also made for sizable low-level wind shear in the area near St Joseph and eastward, upping the potential for tornadoes.</p><p>We headed for St Joseph around 1:15 pm CDT, but were delayed helping a family with car and other issues along I-29 near St Joseph. As a result, with storms erupting west of St Joseph, we missed the first tornado just west of St Joseph near Troy, Kansas at roughly 2:12 pm CDT. But we could see a mesocyclone and lowering associated with the same storm looking southwest from north of St Joseph around 2:25 pm CDT:</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhH6BYZN_FiBKtN7mp2Vv84jvnE2_NcMJ_OiNT5u2aRsRCDQgUenEuXtLWkdH89-uWGoYDfDC77dk09eIYG9Ciw5rXyNh9d8pMXIfc4mwP-BAIHtzXgT7aT8r2EHcaRBnUjw14u-wALBLoc/s900/102421nwMOmeso_srd1_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="500" data-original-width="900" height="356" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhH6BYZN_FiBKtN7mp2Vv84jvnE2_NcMJ_OiNT5u2aRsRCDQgUenEuXtLWkdH89-uWGoYDfDC77dk09eIYG9Ciw5rXyNh9d8pMXIfc4mwP-BAIHtzXgT7aT8r2EHcaRBnUjw14u-wALBLoc/w640-h356/102421nwMOmeso_srd1_anno.jpg" width="640" /></a></div><br /><br /><p></p><p>We moved east from Savannah, MO to follow this mesocyclone as it moved east-northeastward along the warm frontal boundary, and with cloud bases lowering in the warm frontal mixing zone, we watched what appeared to be a brief tornado that lasted 30-45 seconds, looking to our south-southwest from north of Avenue City (northeast of St Joseph):</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEimcU5ptPKzQATCeFKBqBerWYlBOVIqJN76FkRryktDxI02avTmOmMD1qdy5IzFXpCnBBcPckQjhfkJfVHhXMx9K-ys-v3_0wgjCc8RsGC5imGTeF1v9hdwETSA9ujDcB3WkuyGqSaO1Cs2/s896/102421nwMOtor_srd2_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="504" data-original-width="896" height="360" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEimcU5ptPKzQATCeFKBqBerWYlBOVIqJN76FkRryktDxI02avTmOmMD1qdy5IzFXpCnBBcPckQjhfkJfVHhXMx9K-ys-v3_0wgjCc8RsGC5imGTeF1v9hdwETSA9ujDcB3WkuyGqSaO1Cs2/w640-h360/102421nwMOtor_srd2_anno.jpg" width="640" /></a></div><br /><br /><p></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>On the satellite photo shown earlier, the black arrow indicates the cell cluster that produced this probable brief tornado east of the surface low.</p><p>We intercepted this same mesocyclone near Rochester, MO, watching leaves swirling in the air and Shawna fascinated by wispy cloud filaments accelerating rapidly upward into the updraft as it passed just in front of us. Here's the mesocyclone viewed moving away from us on Hwy 169, with both the flanking line and short updraft tower visible looking to our northeast:</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhm0DkEIAj6newsaTgc0-cPUktZbyc7iWPBRIK85QK9T2xU5lQSpd7jSGiL3cv4n1jtz-tqZrQGxyAA0alRQTUbLW8crtvtQZC74HtiGMj0urJQoOqSvgBscYCcuv5M6hMcKBSn2028mdE-/s648/102421nwMOmeso_srd3_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="648" data-original-width="401" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhm0DkEIAj6newsaTgc0-cPUktZbyc7iWPBRIK85QK9T2xU5lQSpd7jSGiL3cv4n1jtz-tqZrQGxyAA0alRQTUbLW8crtvtQZC74HtiGMj0urJQoOqSvgBscYCcuv5M6hMcKBSn2028mdE-/w248-h400/102421nwMOmeso_srd3_anno.jpg" width="248" /></a></div><p></p><p>We had to drop south to Hwy 6 to head east and catch up with the mesocyclone along I-35, which took some time. Meanwhile, our storm had combined with another nearby cell to form a supercell that produced a weak tornado southwest of Pattonsburg MO around 3:35 pm CDT that we couldn't see.</p><p>When we headed north on I-35 toward Pattonsburg, we could see the storm's mesocyclone again, with rapidly-moving cloud tags and brief funnels visible looking toward the northeast located in an area just east of Pattonsburg around 3:50 pm CDT:</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhn7_rQ__yQ9ygbkZ6IAuhSZawkUEJOouvzdlYwtUfqBeBqaNSZwmeLbiX-udGgl8pkKeryDmsm01Hp2tZkgHiPAHkPbJHqBJZR6fzYQkoKwXWIuKrGo7u0mhwl6ugZMZwXK1FEmGnd1_Gs/s820/20211024_155101_crop_adj_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="576" data-original-width="820" height="450" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhn7_rQ__yQ9ygbkZ6IAuhSZawkUEJOouvzdlYwtUfqBeBqaNSZwmeLbiX-udGgl8pkKeryDmsm01Hp2tZkgHiPAHkPbJHqBJZR6fzYQkoKwXWIuKrGo7u0mhwl6ugZMZwXK1FEmGnd1_Gs/w640-h450/20211024_155101_crop_adj_anno.jpg" width="640" /></a></div><br /><br /><p></p><p>After that, with the storms moving away from us at close to 40 mph, and hilly, tree-covered terrain to our east and northeast, we decided to head back to Kansas City. </p><p>Out of reach to our southeast, we could see what had coalesced into a separate supercell between Cameron and Chillicothe, MO, and this storm produced several tornadoes, including the large tornado that later hit Purdin, MO shortly before 5:00 pm CDT doing EF2 damage (see image of that tornado below by Stephen Jones):</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjMoGFxX50sphHbd0Ah-6PN3kgR0zwG_x8Mzwrp1k4VVMUX1sIMxJNnPgE4sDb_VIbV6DEcN0eN-Zbt3JtfV3AfnJ38DQM3Mif4kloQMZn5d-upxSMvMNLbUdGQtp7wcCGWsEbsQx0ix9VN/s613/102421ncMOtor_sj1_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="353" data-original-width="613" height="368" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjMoGFxX50sphHbd0Ah-6PN3kgR0zwG_x8Mzwrp1k4VVMUX1sIMxJNnPgE4sDb_VIbV6DEcN0eN-Zbt3JtfV3AfnJ38DQM3Mif4kloQMZn5d-upxSMvMNLbUdGQtp7wcCGWsEbsQx0ix9VN/w640-h368/102421ncMOtor_sj1_anno.jpg" width="640" /></a></div><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p>The 3-panel radar image below shows the evolution of storms between 2:12 pm CDT (1912 UTC) and 3:55 pm CDT (2055 UTC), with the small white arrow indicating the northern cell(s) we were following and documenting near the warm front:<div><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEihX6JtU4ydMSFk6yQGogD13MND2R2x3uWWOJayCvMBhiF_KbWA2xnFeppnJrryoOeb9O4fr6bUXnelCy_9M0PR4xsgGRIc0sX0u1b7OGi7F5bHJZC6f-SdfahTK3EguSe4STCDeUcQhrcH/s939/102421rd1912-1944-2055eax_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="361" data-original-width="939" height="246" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEihX6JtU4ydMSFk6yQGogD13MND2R2x3uWWOJayCvMBhiF_KbWA2xnFeppnJrryoOeb9O4fr6bUXnelCy_9M0PR4xsgGRIc0sX0u1b7OGi7F5bHJZC6f-SdfahTK3EguSe4STCDeUcQhrcH/w640-h246/102421rd1912-1944-2055eax_anno.jpg" width="640" /></a></div><br /><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div>The more southern cell west of Chillicothe (CDJ) on the last panel above is the one that produced the most tornadoes, including the EF2 Purdin tornado. <p>Most cold-core tornado settings associated with mid-level lows play out fairly quickly with brief, weak tornadoes. With the EF2 Purdin tornado, this case was an exception that featured a broad (rather than narrow) warm sector, and instability (mlCAPE > 1500 J/kg, not shown) and low-level wind shear (0-1 storm-relative helicity or SRH > 200 m2/s2, not shown) increasing during the afternoon near and just south of the warm front into north-central Missouri. </p><p>This is highlighted in the panels below from the SPC mesoanalysis showing the Tornadic Energy-Helicity Index (TEHI, combining CAPE, SRH, and deep-layer shear with other parameters) at 1:00 pm CDT (1800 UTC) and 4:00 pm CDT (2100 UTC):</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi9X-Ks5hTWT68Hb3uvjzUqcUT5c3YWMbJ_HFmjsTK1rCuQkItRlWnBZiVyqeJ9ZTfwmnaQlAm4rADjhOl1cDsRi2x8L-D-5vKjcwDrstqWChwPVVBKzMvsk19FkYAYuQ6zcbXzRs2292lC/s787/102421spctehi18-21z_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="466" data-original-width="787" height="378" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi9X-Ks5hTWT68Hb3uvjzUqcUT5c3YWMbJ_HFmjsTK1rCuQkItRlWnBZiVyqeJ9ZTfwmnaQlAm4rADjhOl1cDsRi2x8L-D-5vKjcwDrstqWChwPVVBKzMvsk19FkYAYuQ6zcbXzRs2292lC/w640-h378/102421spctehi18-21z_anno.jpg" width="640" /></a></div><br /><br /><p></p><p>Notice the TEHI "max" of 3.0+ over north-central Missouri at 2100 UTC (2nd panel above) before the Purdin tornado. </p><p>Later that evening, the environment over east-central and southeast MO away from the cold-core mid-level low over Iowa became quite favorable for strong tornadoes (hinted at in the last TEHI panel above) when storms there became supercells that produced EF3 tornadoes after dark at St Mary, MO and Fredericktown MO.</p><p>It may be a while before I post again, so I just want to express my appreciation to all who follow and give me feedback about my work and severe weather posts. Thanks a bunch, everyone! </p><p>- Jon Davies 10/29/21</p><div><br /></div></div>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com5tag:blogger.com,1999:blog-2399626414603781513.post-59008258839908022722021-06-23T09:08:00.015-07:002021-06-23T11:10:53.389-07:00EF3 tornado in Chicago suburbs on June 20, 2021: NOT a QLCS tornado<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiyFKnACR2txoY8QJrfa5wykpe6nFE8-Xtqh8Tnj9EJD3k6C9O1p_jUKU-a61S_e7P_7c-C78q7SF7fcj-n5-hifeJSYMRoWkgSGUsEff7eK3_ZDmCALaxAXik16b1fI0gbIVPfL1q8Cj-5/s745/062021neILtor_ms_rdrsrv0411z_lot.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="745" data-original-width="645" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiyFKnACR2txoY8QJrfa5wykpe6nFE8-Xtqh8Tnj9EJD3k6C9O1p_jUKU-a61S_e7P_7c-C78q7SF7fcj-n5-hifeJSYMRoWkgSGUsEff7eK3_ZDmCALaxAXik16b1fI0gbIVPfL1q8Cj-5/w346-h400/062021neILtor_ms_rdrsrv0411z_lot.jpg" width="346" /></a></div><br /><p>Sunday night's tornado after dark (photo above) that struck the western Chicago suburbs of Naperville, Woodridge, and Darien in Illinois (IL) shortly after 11:00 pm CDT injured 11 people. Fortunately, no one was killed, with good watches and warnings in advance. The tornado was EF3 in intensity, and left a damage path of around 16 miles in length.</p><p>I noticed on social media early on that several people called this a "QLCS tornado" (QLCS stands for 'quasi-linear-convective-system'), a type of non-supercell tornado that can occur within bowing squall lines. It is true that the tornadic storm was embedded within a line of storms. However, to be clear and accurate, this was definitely _not_ a QLCS tornado -- it was a <i>supercell tornado</i> with a well-detected mesocyclone (rotating updraft) on radar, seen on the inset in the tornado photo above showing storm-relative velocity. Because it was a supercell tornado with a distinct mesocyclone on radar before the tornado, a radar-based tornado warning could be issued for parts of DuPage County (the county where Naperville is located) around 20 minutes before the tornado developed. </p><p>QLCS tornadoes tend to be brief, relatively weak, and more difficult to see on radar, making them more difficult to warn. A QLCS tornado that struck the southeast corner of El Reno, Oklahoma after dark on the evening of May 25, 2019 (not shown) lasted only 4 minutes and traveled only around 2 miles. It was briefly detectable on radar due to the close proximity of El Reno to the NWS radar near Norman, but could only be warned with 2 minutes lead time, not even enough time for sirens to sound in El Reno before the tornado struck. It killed 2 people and injured 29, even though deaths and injuries are rare with QLCS tornadoes.</p><p>Back to June 20, 2021, the 3-panel composite reflectivity radar image below shows the broad evolution of the line of storms and the embedded supercell and mesocyclone (small white circle) from 10:45 pm to 11:15 pm CDT:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEivZculGrsfst7rPtCMdnq309IBdKUqWV0kqhxTla2SaVWsQ-NcD-b1IynDEPAJXv9FDtEUlQyQuYY-BKqAMStLGB1eB6-C-9-_ZRoIoot94pOJz9j82eJe6eUIEkuLsNEx-CXxJUcF25QK/s1109/062121rdrr0345-0415il_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="602" data-original-width="1109" height="348" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEivZculGrsfst7rPtCMdnq309IBdKUqWV0kqhxTla2SaVWsQ-NcD-b1IynDEPAJXv9FDtEUlQyQuYY-BKqAMStLGB1eB6-C-9-_ZRoIoot94pOJz9j82eJe6eUIEkuLsNEx-CXxJUcF25QK/w640-h348/062121rdrr0345-0415il_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>It is important to remember that it is not unusual for supercells to be embedded within a line of storms, but that does not mean that tornadoes associated with such storms are QLCS tornadoes. A primary difference is the mid-level mesocyclone visible on radar, often in advance of a tornado. </p><p>A brief look at the local setting and environment over northern IL on Sunday evening June 20th showed a quasi-stationary outflow boundary associated with the east-northeast to west-southwest line of storms across the Naperville-Chicago area:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh_U3FoUXHElCZFHlGry1Z6veKmqk9HQO0lSUb594VHgLTcQGy3Sg_da_IYej5WJIeYKQo5qVOACt4sElzI47hhh-7jESCLKOZmbIojYHJvQ8a4oZgI_fsbQyHXuvHjxmgUrYcau45TK3dl/s530/062121sfc0358anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="530" data-original-width="529" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh_U3FoUXHElCZFHlGry1Z6veKmqk9HQO0lSUb594VHgLTcQGy3Sg_da_IYej5WJIeYKQo5qVOACt4sElzI47hhh-7jESCLKOZmbIojYHJvQ8a4oZgI_fsbQyHXuvHjxmgUrYcau45TK3dl/w638-h640/062121sfc0358anno.jpg" width="638" /></a></div><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>This boundary may have helped to generate the tornado as the embedded parent supercell moved east along it, taking advantage of increased low-level wind shear and convergence on and near the boundary, as well as the temperature/moisture contrast across it.</p><p>SPC mesoanalysis graphics near the time of the tornado also showed the environment near the boundary over northeast IL to be supportive of supercell tornadoes: </p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjC5XnacVGMqvuzCFhlXCZ20qhewqGD2StTOLQsSZ8XC_tRHyF_9D2JEPYP3eNsArIh_IUSJFgXCL8JU2nkukgjVqjI30bBU9P3M0Wc9RyQacMDIxlPY7SBkqub8Mtv95QTmDR2YzIa3cG_/s1067/062121spctehi-stpc05_04_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="579" data-original-width="1067" height="348" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjC5XnacVGMqvuzCFhlXCZ20qhewqGD2StTOLQsSZ8XC_tRHyF_9D2JEPYP3eNsArIh_IUSJFgXCL8JU2nkukgjVqjI30bBU9P3M0Wc9RyQacMDIxlPY7SBkqub8Mtv95QTmDR2YzIa3cG_/w640-h348/062121spctehi-stpc05_04_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>In particular, a version of the energy-helicity index (a parameter combining low-level wind shear and CAPE/instability) augmented by enhancements/limitations related to deep-layer wind shear, 0-3 km CAPE, and estimated cloud-base heights (see 1st panel above) showed a supportive environment for supercell tornadoes in the Napervlle-Chicago area. Also, a new version of the significant tornado parameter (2nd panel above) using low-level wind shear (storm-relative helicity or SRH) in the lowest 500 m above ground indicated similar support for supercell tornadoes.</p><p>A short-term HRRR model forecast of the basic energy-helicity index from early evening also showed maximized combinations of SRH and CAPE near and just south of the local boundary across the Naperville-Chicago area:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiLGXllZcsJIiazQcsj5wgL_FCXU-7sUro4Likxoz5-2LyAHBOmMpfF5LEJFb3clydSweSjI78PiC7He7631SxKFDOySD2kTbYp-nrMJ-4AacNsg14XP5iFg-E0PX00sBtp7XHr0pb9daNM/s706/062121hrreh104f04pvt_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="706" data-original-width="613" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiLGXllZcsJIiazQcsj5wgL_FCXU-7sUro4Likxoz5-2LyAHBOmMpfF5LEJFb3clydSweSjI78PiC7He7631SxKFDOySD2kTbYp-nrMJ-4AacNsg14XP5iFg-E0PX00sBtp7XHr0pb9daNM/w557-h640/062121hrreh104f04pvt_anno.jpg" width="557" /></a></div><p>So, ingredients supportive of significant supercell tornadoes were definitely in place over northeast IL late on the evening of June 20, 2021.</p><p>Again, the fact that the tornado was associated with a supercell and detectable mesocyclone on radar made warning in advance more possible, an important difference in contrast to QLCS tornadoes. QLCS tornadoes are shallower circulations that are more transient and harder to detect on radar, and therefore more difficult to warn.</p><p>It is important to understand this distinction.</p><p>- Jon Davies 6/23/21</p><p> </p>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com3tag:blogger.com,1999:blog-2399626414603781513.post-8755448870840271162021-05-13T16:36:00.021-07:002021-05-14T04:18:45.607-07:00The May 8, 2021 HP supercell in central Kansas & comparison to the May 1, 2018 Tescott tornado setting<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjLsvnKDpRitKUoHiaIUrMMtARY2yVxOzDZM0Cij8mkyCOodHjUfP7r9Z65T9XPCX8fZQYITx4n_3TgAPPKCLm-GTkS8M5MW1hDXkvrBbvzOdz0gYwcp4RAYrQ-rOrfkht8OLfhBxEPX02d/s905/Img_4105_crop2_adj_sml%2528c%2529.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="576" data-original-width="905" height="408" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjLsvnKDpRitKUoHiaIUrMMtARY2yVxOzDZM0Cij8mkyCOodHjUfP7r9Z65T9XPCX8fZQYITx4n_3TgAPPKCLm-GTkS8M5MW1hDXkvrBbvzOdz0gYwcp4RAYrQ-rOrfkht8OLfhBxEPX02d/w640-h408/Img_4105_crop2_adj_sml%2528c%2529.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>Last Saturday's HP supercell at early evening west of Salina (see Shawna's dynamic photo above) was our first chase in nearly a year, as Kansas (KS) has been rather quiet concerning severe weather recently. The setting did have some similarities to the <a href="http://davieswx.blogspot.com/2018/05/kansas-tornado-season-finally-begins.html" target="_blank">May 1, 2018 tornadic supercell</a> set up northwest of Salina three years ago in that storms formed in west-central KS at the north edge of a "cap" (warm layer of air aloft near 10000 ft MSL), and in each case at least one storm moving east-northeast became an evening supercell near Ellsworth, KS. </p><p>But Saturday's supercell was non-tornadic and high-precipitation ("HP") in character, while the May 1, 2018 supercell produced an EF3 tornado on the ground for around 14 miles. Sometimes it is informative to compare cases in the same geographic area that appear to have similar settings at first glance, but end up with very different results, which I'll do briefly here, as well as summarize our storm chase. </p><p>The NWS-analyzed surface map at 7:00 pm CDT (0000 UTC 5/9/21) in the first panel below showed a double-barrel surface low near a triple point over west-central KS, northeast of which storms had formed at mid to late afternoon... a classic severe weather setting sometimes associated with tornadoes:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjboDifwxCP-jEIMSPMpBSqRhzld8h3aHpC7kuEVb5KvlZikD3QcDlpNco98cqFr8d5dRM42OK5jDMNQuaKiiel_NApTiHqPup0OtKZhRXPTulgI1PEREs7Z1gG3he74hrzeqs2dKUizxMy/s751/050921sfc00z-nameh100f12_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="464" data-original-width="751" height="397" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjboDifwxCP-jEIMSPMpBSqRhzld8h3aHpC7kuEVb5KvlZikD3QcDlpNco98cqFr8d5dRM42OK5jDMNQuaKiiel_NApTiHqPup0OtKZhRXPTulgI1PEREs7Z1gG3he74hrzeqs2dKUizxMy/w640-h397/050921sfc00z-nameh100f12_anno.jpg" width="640" /></a></div><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>The 2nd panel above also shows the NAM model 12-hr forecast of the 0-1 km energy helicity index (EHI, combining instability and low-level wind shear) valid at the same time as the surface map in the first panel. EHI values approaching 2.0 into central KS suggested that tornadoes might be a possibility, along with the morning SPC outlooks (not shown) that showed a 5% probability of tornadoes in central and north-central KS... not high but not insignificant, either.</p><p>Shawna and I followed a couple cells that had formed west and southwest of La Crosse, and had became a loose cluster of storms as they moved north of Great Bend. Out of this "cluster", a high-based supercell formed after 7:00 pm CDT west of Ellsworth, KS:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhZkh_jZ57Kxa3FnTocchTngvImuegjjFEzi_Cvai9vpb22zNksN_q2nmtFB8bMfX5fmVnCmyy-BVmQZmdKeEmdw3c2kJAamyxPRzSHlUx7_xfcPMHRQ7FUbBczcirEErYnHTgul3Ll8crb/s871/20210508_193641_crop_adj_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="576" data-original-width="871" height="265" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhZkh_jZ57Kxa3FnTocchTngvImuegjjFEzi_Cvai9vpb22zNksN_q2nmtFB8bMfX5fmVnCmyy-BVmQZmdKeEmdw3c2kJAamyxPRzSHlUx7_xfcPMHRQ7FUbBczcirEErYnHTgul3Ll8crb/w400-h265/20210508_193641_crop_adj_anno.jpg" width="400" /></a></div><p>This storm moved across Ellsworth producing wind gusts, heavy rain, and some nickel-size hail, and we were able to get in front of it again on Hwy 140 heading east toward Brookville and Salina. Here's Shawna's shot of this high-based cell near Carneiro looking west-southwest as I snapped some pics in the foreground:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgJePkd16WB5GCs9UVr9muNn7vLzOGL_m3pzWQ7kM2gHsqjj5k6DOoXb7a7XlVI9r31tSSkE8xpQlmJriyOwFlK8pzFM4k1FrRK-flSrzd_EqIkcyehFRSxTz4Chcwe3QxDhmmRk813r1P0/s720/Img_4098_adj_sml_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="720" data-original-width="529" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgJePkd16WB5GCs9UVr9muNn7vLzOGL_m3pzWQ7kM2gHsqjj5k6DOoXb7a7XlVI9r31tSSkE8xpQlmJriyOwFlK8pzFM4k1FrRK-flSrzd_EqIkcyehFRSxTz4Chcwe3QxDhmmRk813r1P0/w294-h400/Img_4098_adj_sml_anno.jpg" width="294" /></a></div><p>This HP storm really took on some impressive structure west of Brookville, with a dark roiling high-based shelf (the storm was outflow-dominant at this point, with winds already shifting to the west at our location in front of the shelf). Staccato cloud-to-cloud and cloud-to-ground lightning bolts were visible along the outflow shelf, and I took the picture below of this "angry" supercell looking north (similar to Shawna's photo at the top of this post, but without the cool lightning) from west of Brookville as the storm approached us:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgbh92qw3zLq8XgvHEUJ-qT9NJkG6aiaZ3C8N6cFb4B6dhDfkninIbSQKW2SCgQp1x_b4XltTCdM68LwqCHHeL6XUeY_Tn6LB_0OZZvB09LVhdC8HojzUDDjwwTXWMts36NAJ2exitrSoaR/s768/20210508_201130_adj_sml%2528c%2529.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="576" data-original-width="768" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgbh92qw3zLq8XgvHEUJ-qT9NJkG6aiaZ3C8N6cFb4B6dhDfkninIbSQKW2SCgQp1x_b4XltTCdM68LwqCHHeL6XUeY_Tn6LB_0OZZvB09LVhdC8HojzUDDjwwTXWMts36NAJ2exitrSoaR/w400-h300/20210508_201130_adj_sml%2528c%2529.jpg" width="400" /></a></div><p>The high outflow base and outflow-ish nature of the storm eliminated thoughts of tornadoes at this point, but it was a beautiful storm in a pretty setting (the Smoky Hills). We reached Salina with darkness upon us, and after watching lightning for a while, we headed back to Kansas City.</p><p>One problem working against tornado potential on this day appeared to be high lifting condensation level (LCL) heights (up near 2000 m above ground) that allowed evaporative cooling as rain fell through the deep sub-cloud layer, generating cool outflow air that undercut the storm's rain-wrapped mesocyclone. Another issue was somewhat weak winds aloft in mid-levels that generated just enough deep-layer shear (25-30 kt) to support a supercell, but one that was HP in character, adding to the outflow-ish nature of the storm. The morning HRRR model forecast these limitations rather well:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEik4iweC3JuYRitZyEiFSYis06h4M_UFUamQm-s_npIAPaOsdCf1-szgxJDZfriUBYaAPWUCeR3hZh_whfVq3xuvZ8MbRZdalhbzO3ITG3386qGqL6PfbmIUZHTJW3V3y3QSjXmDVABDJWS/s1065/050921hrr_sblcl-06s_00f12pvt_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="610" data-original-width="1065" height="366" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEik4iweC3JuYRitZyEiFSYis06h4M_UFUamQm-s_npIAPaOsdCf1-szgxJDZfriUBYaAPWUCeR3hZh_whfVq3xuvZ8MbRZdalhbzO3ITG3386qGqL6PfbmIUZHTJW3V3y3QSjXmDVABDJWS/w640-h366/050921hrr_sblcl-06s_00f12pvt_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>But the morning HRRR model also did a good job forecasting the supercell at early evening, with a mid-level rotation track indicated west of Salina:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgzfFzsFqw1qDUsFcrzm-LSr4m7onfCnGMZ8txI045UTIAh9579rRJLVOx-9qO0_2B2JeSNWMmpmJCMRk87kf3nk6zxmrngBooizAGRIq-1lRHtwcM_M8jzRgXfBmyT8emlJc0MoPdKbzah/s537/050921hrrrdr00f12_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="522" data-original-width="537" height="389" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgzfFzsFqw1qDUsFcrzm-LSr4m7onfCnGMZ8txI045UTIAh9579rRJLVOx-9qO0_2B2JeSNWMmpmJCMRk87kf3nk6zxmrngBooizAGRIq-1lRHtwcM_M8jzRgXfBmyT8emlJc0MoPdKbzah/w400-h389/050921hrrrdr00f12_anno.jpg" width="400" /></a></div><p>As mentioned earlier, the track and timing of this supercell were similar to the May 1 Tescott tornadic storm back in 2018. However, there were some key differences in the environments, as indicated by the red highlight boxes in the table of parameter comparisons from SPC mesoanalysis graphics (not shown) between the two events listed below:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiCiOBbtpmoJ9MjUOrYB-oGLRyrjhsOvVL1qvI6gUfaf3_qCSi8JIP2x_5MjwLpuitBvm-ICYKHvoY7FPE217MZ8ata_Em32PdLreYlCucBefKKOY3-L1bQDw3LcEWyVbL4COTRu-iPRiW6/s441/050921par_table_sln00-01z_compare-with-050218.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="260" data-original-width="441" height="236" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiCiOBbtpmoJ9MjUOrYB-oGLRyrjhsOvVL1qvI6gUfaf3_qCSi8JIP2x_5MjwLpuitBvm-ICYKHvoY7FPE217MZ8ata_Em32PdLreYlCucBefKKOY3-L1bQDw3LcEWyVbL4COTRu-iPRiW6/w400-h236/050921par_table_sln00-01z_compare-with-050218.jpg" width="400" /></a></div><div class="separator" style="clear: both; text-align: center;"><br /></div><p>Apart from smaller low-level wind shear (0-1 km storm-relative helicity or SRH) on May 8, the main differences were much higher LCL heights compared to May 1, 2018, and smaller deep-layer shear (0-6 km bulk wind difference or 6BWD), confirming the same issues raised by the HRRR model forecast discussed earlier.</p><p>Here's a RAP model analysis sounding (similar to what is used in generating SPC mesoanalysis graphics) at Ellsworth, KS valid at 7:00 pm CDT on May 8, 2021, highlighting in yellow and red these same problematic issues in the environment regarding tornado potential at the time the supercell was ramping up west of Ellsworth:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgp0QEYiILyoDYyMrIlKn1zqymv3P7-NZJHZUx8DI_h5n8fJXvYa1zGBTSilOr3YLNDBwqnSzS9QLmO3qH0PXJzu7Hn6e1H-VOoebVcNxCgUY0KPLrKAlaZCpePFpcADfRY0LrgcnfkdkQH/s1197/050921ellsworthKS00rapa_cod_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="784" data-original-width="1197" height="420" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgp0QEYiILyoDYyMrIlKn1zqymv3P7-NZJHZUx8DI_h5n8fJXvYa1zGBTSilOr3YLNDBwqnSzS9QLmO3qH0PXJzu7Hn6e1H-VOoebVcNxCgUY0KPLrKAlaZCpePFpcADfRY0LrgcnfkdkQH/w640-h420/050921ellsworthKS00rapa_cod_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>This sounding confirms that LCL heights and deep-layer shear were two negative factors in the environment that probably worked against tornadoes on May 8.</p><p>As the evening went on, low-level shear increased (SRH, not shown) and LCL heights lowered quite a lot (not shown) as surface temperatures cooled. But, low-level stability (convective inhibition or CIN) also increased (not shown), suggesting that storms were not strongly surface-based near and after dark, so that much of the instability was coming from well above the ground, working against the formation of tornadoes.</p><p>Before closing, it is interesting to look at a later RAP model analysis sounding for Salina at 10:00 pm CDT (0300 UTC 5/9/21). This sounding was estimating the environment in front of a 2nd supercell that formed behind the one we chased earlier, and was tornado-warned based on radar-detected mid-level rotation around 10:11 pm CDT:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhojLdMglTZVwgtZ3DfREwf7HRPiIyNehZ6eeLSPsxcO4b7E2fSnJ6p0YMp5Q8SwfFkDdvB4JotkPnzp8fHFQyQf3IltXnrUweLYoEDX2K1xI8skaRrOYdXkMwDw84yWMJal7HRDMpyK2DY/s1198/050921sln03rapa_cod_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="784" data-original-width="1198" height="418" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhojLdMglTZVwgtZ3DfREwf7HRPiIyNehZ6eeLSPsxcO4b7E2fSnJ6p0YMp5Q8SwfFkDdvB4JotkPnzp8fHFQyQf3IltXnrUweLYoEDX2K1xI8skaRrOYdXkMwDw84yWMJal7HRDMpyK2DY/w640-h418/050921sln03rapa_cod_anno.jpg" width="640" /></a></div><br /><p><br /></p><p>Notice how large the CIN (blue area on the thermodynamic diagram) had become after dark, with more than 225 J/kg of inhibition. This was the result of outflow air behind the earlier supercell, now bowing out well east of Salina (SLN) on the radar image below, shortly before 10:00 pm CDT:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh1WEMhwovYEGeF5rhXhO0PEDx7I4Y5XlfEzdDv-ci-xLfYRsovMMNFMNGCEQvwKIpa4L-_xsaUHUDw_oig4C0XbwMOhJLsmxbP7PQouprg63ULPqGh4X5rgI-jMMJMqmDDDKBeumCoqHU4/s482/050921rdrrr0240ict_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="476" data-original-width="482" height="395" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh1WEMhwovYEGeF5rhXhO0PEDx7I4Y5XlfEzdDv-ci-xLfYRsovMMNFMNGCEQvwKIpa4L-_xsaUHUDw_oig4C0XbwMOhJLsmxbP7PQouprg63ULPqGh4X5rgI-jMMJMqmDDDKBeumCoqHU4/w400-h395/050921rdrrr0240ict_anno.jpg" width="400" /></a></div><p>I've indicated on the radar image the new tornado-warned cell west of Salina and the "fine line" showing the trailing outflow boundary from the earlier supercell (white arrows). Also note the temperature and dew point at Salina (63 over 59 deg F) within this outflow just before 10:00 pm CDT. All this information suggests that this new supercell was ingesting cool outflow air that would undercut and eliminate any true tornado potential with this new supercell.</p><p>I was a little surprised that NWS issued the tornado warning, based on radar and environmental data above. Although ping-pong size hail fell with this 2nd supercell, no tornado occurred and the warning was soon dropped. This re-affirms how outflow near the ground can really interfere with tornado production. </p><p>The May 8, 2021 central KS case is an interesting case to study regarding how factors like LCL height and relatively weak deep-layer shear can limit supercell tornado potential. These are two easy-to-overlook ingredients that require careful consideration in tornado forecasting.</p><p>- Jon Davies 5/13/21</p>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com0tag:blogger.com,1999:blog-2399626414603781513.post-35366617746163449232021-04-01T13:41:00.011-07:002021-04-01T15:08:30.826-07:00March 25, 2021 deadly tornado outbreak in Alabama and Georgia<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEipSwwUNVt7R5MvD4okpr69wkg1s789j6eWgzlkhGCM_q6eYupNwOlvFn3NS-LAID9ROkKuJz4Y9YGrjTy3FWYdLqv1_dkrR9rex5ET_eELjdkOCGXXK6J-J74G5FgMogHKXQXYGyAh2rSW/s660/SRH-CAPE_compare_031721_032521_042711.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="660" data-original-width="606" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEipSwwUNVt7R5MvD4okpr69wkg1s789j6eWgzlkhGCM_q6eYupNwOlvFn3NS-LAID9ROkKuJz4Y9YGrjTy3FWYdLqv1_dkrR9rex5ET_eELjdkOCGXXK6J-J74G5FgMogHKXQXYGyAh2rSW/w588-h640/SRH-CAPE_compare_031721_032521_042711.jpg" width="588" /></a></div><p>One week ago today, a deadly tornado outbreak in Alabama (AL) and Georgia (GA) caused 6 deaths and a number of injuries, making it the deadliest tornado episode of 2021 so far.</p><p>Similar to March 17, 2021 (see toward the end of my post <a href="http://davieswx.blogspot.com/2021/03/active-march-severe-weather-pattern.html" target="_blank">here</a>), the outbreak was well-forecast and well-warned, and as a result many lives were likely saved, even considering the deaths that did occur. As a result, some people on Twitter have mentioned the famous April 27, 2011 tornado "super outbreak" ten years ago, when over 200 tornadoes occurred on one day in the Dixie states and more than 300 people were killed. </p><p>The graphic at the top of this page offers a quick comparison of the tornado environments between that day back in 2011 and the recent outbreaks in AL on March 25 and March 17, 2021 using a scatter-diagram showing storm-relative helicity (SRH, a measure of low-level wind shear) and mixed-layer CAPE (a measure of instability). Sizable low-level wind shear can generate low-level storm rotation leading to supercell tornadoes, and CAPE (convective available potential energy) helps support and sustain those rotating storm updrafts.</p><p>The big pink dot in the middle of the diagram up at the top of this page is representative of the environment on April 27, 2011, showing an unusually large combination of SRH and CAPE leading to the massively deadly tornado outbreak that day nearly ten years ago. It's pretty clear that 4/27/11 had much larger support for strong and violent tornadoes than either 3/25/21 or 3/17/21.</p><p>Getting back to 2021, I've plotted on the same diagram four of the strongest tornadoes from March 25 last week (small yellow-filled dots) and four of the strongest tornadoes from March 17 a couple weeks ago (small red-filled dots), and enclosed those areas on the diagram in black ovals. Comparing 3/25/21 with 3/17/21, it appears that March 25 had somewhat larger low-level wind shear, one difference between the 3/17/21 setting that supported shorter-tracked EF2 tornadoes, and the 3/25/21 setting where tornadoes were stronger (EF3 and EF4) and longer-tracked.</p><p>Another difference between March 25 and March 17 (not shown here) was deep-layer wind shear, where 0-6 km bulk wind difference (BWD) on 3/25/21 in central AL averaged near 70 knots or more, whereas on 3/17/21 the 0-6 km BWD averaged only near 50 knots, In other words, the general wind fields and resulting wind shear at multiple levels appeared stronger on March 25, 2021, helping to generate stronger and longer-tracked tornadoes like this one near Greensboro AL and west of Centreville AL at mid-afternoon:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhATM7-SxQwyGqh4oGyAE9_Gi-SG5iySuBa6_q1LLEPe_7F2Bk_T3f26svkai5H0jw_N-h3zNNvPPzSFAGym7MVaUIKKUkjBGPawqA9dD7yV57G28mdzaw993p_apU-RJoP03edYaptDh3S/s795/032521cALtor_mo_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="478" data-original-width="795" height="384" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhATM7-SxQwyGqh4oGyAE9_Gi-SG5iySuBa6_q1LLEPe_7F2Bk_T3f26svkai5H0jw_N-h3zNNvPPzSFAGym7MVaUIKKUkjBGPawqA9dD7yV57G28mdzaw993p_apU-RJoP03edYaptDh3S/w640-h384/032521cALtor_mo_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>To very briefly review the setting on March 25, here's the tracks of EF2+ tornadoes last Thursday plotted on top of a surface map at 2100 UTC (4:00 pm CDT) on 3/25/21:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiGnovFgha4t-hBixM7-2hFD53E4FwGDLjwchWRWjq6qq6s-pXTHBgToDWRjCbBu0tg5BQp-s35gO7ZCfLzjAsTlu5E7969sO5aBpDvIC9VJMkB8JjTXbAkht7ZOt5JJpQNM-5q3Gtn3hPs/s716/032521sfc21z_seus2_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="526" data-original-width="716" height="470" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiGnovFgha4t-hBixM7-2hFD53E4FwGDLjwchWRWjq6qq6s-pXTHBgToDWRjCbBu0tg5BQp-s35gO7ZCfLzjAsTlu5E7969sO5aBpDvIC9VJMkB8JjTXbAkht7ZOt5JJpQNM-5q3Gtn3hPs/w640-h470/032521sfc21z_seus2_anno.jpg" width="640" /></a></div><br /><p><br /></p><p>And here's an SPC mesoanalysis graphic of composite tornado parameters at 1800 UTC (1:00 pm CDT):</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgLxOrEcWrOYBD30XMVnH9fRKDpHAMge1PhtYJx2RqzKTt6KKY2QQFv7hoAqe5JoDxbfO7vxMgGb47sDyqYuvf8I801icFv3pUJ0bMrzslcK5E_OLcILH6nWzO1tGHHf7amcaGrwTpWRAij/s872/032521spc_stpc05-tehi_18_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="454" data-original-width="872" height="334" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgLxOrEcWrOYBD30XMVnH9fRKDpHAMge1PhtYJx2RqzKTt6KKY2QQFv7hoAqe5JoDxbfO7vxMgGb47sDyqYuvf8I801icFv3pUJ0bMrzslcK5E_OLcILH6nWzO1tGHHf7amcaGrwTpWRAij/w640-h334/032521spc_stpc05-tehi_18_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>The warm sector over central Alabama south of the warm front was where wind shear and instability parameters were maximized and the long-track afternoon tornadoes occurred.</p><p>Here's a composite radar image at 1930 UTC (2:30 pm CDT) just before the town of Ohatchee in east-central/northeast AL was hit by a tornado that killed 5 people. </p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhMwZruDjEfLck1pKUsRx54VIJi-h0WlO3ND8NRmIQjtgh2oHn4CmAWQcdEyxNCSf-j0YDQAEY2MkbsKqWktg48_acCt3bFijfQH_rY47rFOFy5ipQMJSt1IC08lTf7gINUV_WrfnGvLC3L/s645/032521rdrrr1930ms-al_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="645" data-original-width="593" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhMwZruDjEfLck1pKUsRx54VIJi-h0WlO3ND8NRmIQjtgh2oHn4CmAWQcdEyxNCSf-j0YDQAEY2MkbsKqWktg48_acCt3bFijfQH_rY47rFOFy5ipQMJSt1IC08lTf7gINUV_WrfnGvLC3L/w589-h640/032521rdrrr1930ms-al_anno.jpg" width="589" /></a></div><p>And here's a very interesting photo as that killer tornado approached Ohatchee around 1940 UTC (2:40 pm CDT) -- it appears to show two large vortices, reminiscent of the multi-vortex <a href="https://www.weather.gov/ind/palmsuntor" target="_blank">Elkhart Indiana tornado</a> photographed on Palm Sunday in April of 1965:</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiSmRWqziJdM7f4KBdlSRNDniu-rUip6WOv_17hv9sCahysVQQ23KSPURs6utIUxp5XF1ELgknQBOjYL0fi3exnV-x5o77EqSjLshOEacYmjUguZgVLpSP2nSXPC6hgCNweNXhS0YnpHgGl/s958/032521neALtor_unkn2_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="622" data-original-width="958" height="416" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiSmRWqziJdM7f4KBdlSRNDniu-rUip6WOv_17hv9sCahysVQQ23KSPURs6utIUxp5XF1ELgknQBOjYL0fi3exnV-x5o77EqSjLshOEacYmjUguZgVLpSP2nSXPC6hgCNweNXhS0YnpHgGl/w640-h416/032521neALtor_unkn2_anno.jpg" width="640" /></a></div><br /><br /><p></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>This tornado was from the same supercell that produced a 50-mile track EF3 tornado that struck earlier south of Birmingham with damage and injuries. </p><p>And, on the radar image earlier, a new supercell is indicated entering west-central AL that would later generate a strong 80-mile track EF3 tornado starting west of Centreville, AL that at times was more than a mile wide (see the tornado photo earlier by Max Olson):</p><p>Here's a RAP model mid-afternoon analysis sounding at Centreville, AL showing the environment supporting this longest-track tornado of the day that could have possibly been rated EF4 had it directly hit a town:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiNX-X2NVMZN2SIA7c2YoB_6r6z7Q-wZ5nyX6HfJMagNZ84DyAKB9uOyh91Vwsai85Sh5VdJ11EGt9HdFJFIF4c4eFEw43D9ahOXSk-QnJ-XAtbPs-7y4EvULpGXiLlw6w9HVHKUN-heIbC/s1197/032521centrevilleAL21rapa_cod_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="779" data-original-width="1197" height="416" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiNX-X2NVMZN2SIA7c2YoB_6r6z7Q-wZ5nyX6HfJMagNZ84DyAKB9uOyh91Vwsai85Sh5VdJ11EGt9HdFJFIF4c4eFEw43D9ahOXSk-QnJ-XAtbPs-7y4EvULpGXiLlw6w9HVHKUN-heIbC/w640-h416/032521centrevilleAL21rapa_cod_anno.jpg" width="640" /></a></div><br /><p><br /></p><p>With around 300 m2/s2 of 0-1 km SRH, 1400 J/kg of mixed-layer CAPE, over 80 kt of deep-layer shear, and sizable low-level CAPE, this was a fairly potent environment for supporting supercell tornadoes.</p><p>As the outbreak extended into evening on March 25, a new storm became tornadic in central AL around 9:00 pm CDT (0200 UTC 3/26/21, not shown). On the graphic below, the wind and instability environment for this storm at 0300 UTC 3/26/21 on SPC mesoanalysis composite tornado parameters was still quite good for supporting strong or violent supercell tornadoes:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgWzo7oWTQOZTHdVuo0el3LpBsk0Rq5Ajk1Gd_r4EQii5hiWO8ZXYUlCrw_DEzsAlQLfXKBPRRry5u59i5kw_vv3oj-F8koTMbvcm5iWgIKBSLBKuaZ1wVefeFQEK71XrQ00WOksvi7_LLu/s456/032621spctehi03b_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="456" data-original-width="390" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgWzo7oWTQOZTHdVuo0el3LpBsk0Rq5Ajk1Gd_r4EQii5hiWO8ZXYUlCrw_DEzsAlQLfXKBPRRry5u59i5kw_vv3oj-F8koTMbvcm5iWgIKBSLBKuaZ1wVefeFQEK71XrQ00WOksvi7_LLu/w343-h400/032621spctehi03b_anno.jpg" width="343" /></a></div><p>And that's in fact what happened, with a low-end EF4 tornado striking Newnan GA over the border from AL around 0400 UTC (11:00 pm EDT), killing one person. After that, storms tended to outrun the warm sector instability axis as they moved eastward, and tornadoes ceased occurring.</p><p>Finally, to back up in scale and time a bit, here's the NAM model 9-hr forecast of 500 mb features and energy-helicity index (EHI, combining SRH and CAPE) at mid-afternoon on March 25:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiw8_5MNvMH0U1YxqILrK03dvoyvZRfLRk_OqqgdF8k8b86lJ7IjEkNO61XWPy5JGVQjc-Ma2_RbeAdosB5mKJSzBfcOLnetndi1rk_v9WqZaBwsflw1oYKdy8wW47XWB5W9kVGPXORZCyp/s718/032521nam500mb-eh121f09pvt_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="629" data-original-width="718" height="560" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiw8_5MNvMH0U1YxqILrK03dvoyvZRfLRk_OqqgdF8k8b86lJ7IjEkNO61XWPy5JGVQjc-Ma2_RbeAdosB5mKJSzBfcOLnetndi1rk_v9WqZaBwsflw1oYKdy8wW47XWB5W9kVGPXORZCyp/w640-h560/032521nam500mb-eh121f09pvt_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>As on March 17, it was again a classic setting with plenty of SRH and CAPE in an area ahead of a strong trough at 500 mb (this time, a strong mid-level shortwave) where lift and forcing resulted from a "spreading" jet branches pattern ahead of this mid-level disturbance.</p><p>Last Saturday March 29, 2021 saw yet another deadly tornado day within an active sequence of days, with tornadoes in Texas, Louisiana, Arkansas, Tennessee, and Mississippi; one person was killed in northeast Texas (see photo of EF2 tornado near Carthage, Texas below):</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiF-fSmPxzTOKVt5g3n6-kwrZ3T7tfY0L0Qu2YQTyz28jHT4hYBZvhak_pi9s5csUmwTJPp5Nj_QDds1qy5WrEXCyOsiyC1rdYcRUlpPajUUunqvGulERdjnfX2ZinlTdFowMX5mKdAYMaJ/s599/032721neTXtor_cc_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="417" data-original-width="599" height="279" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiF-fSmPxzTOKVt5g3n6-kwrZ3T7tfY0L0Qu2YQTyz28jHT4hYBZvhak_pi9s5csUmwTJPp5Nj_QDds1qy5WrEXCyOsiyC1rdYcRUlpPajUUunqvGulERdjnfX2ZinlTdFowMX5mKdAYMaJ/w400-h279/032721neTXtor_cc_anno.jpg" width="400" /></a></div><p>As I write this, it looks like conditions supportive of tornadoes will take a break and hold off until the middle of next week (around April 7th or 8th?) in the central and southern U.S.</p><p>- Jon Davies 4/1/21 (no April Fooling)</p>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com1tag:blogger.com,1999:blog-2399626414603781513.post-36107725053599637952021-03-24T13:11:00.014-07:002021-03-24T13:31:57.234-07:00Active March severe weather pattern continues across the central and southern U.S.!<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiQh_Xvl7mYJZ2gYatuLmq1ljl1N3DljvC9SSHSurPbccGBwszkIcE9o-NWeJe8MUIWojbiQQQk-_geSzb6BL-B6m41O2SapvJ2IzfBmg9Jq9lXEbI-_mQ808PBrai5plbdDRJqRjJAFuSa/s550/032321wcILtor_st_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="341" data-original-width="550" height="397" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiQh_Xvl7mYJZ2gYatuLmq1ljl1N3DljvC9SSHSurPbccGBwszkIcE9o-NWeJe8MUIWojbiQQQk-_geSzb6BL-B6m41O2SapvJ2IzfBmg9Jq9lXEbI-_mQ808PBrai5plbdDRJqRjJAFuSa/w640-h397/032321wcILtor_st_anno.jpg" width="640" /></a></div><p>After last week's St. Patrick's Day outbreak in the South on March 17 (more about that farther down), yesterday saw yet another cold-core type setting with tornadoes in west-central Illinois (photo above) and southeast Iowa, on top of last week's cold-core activity (see my last blog post <a href="http://davieswx.blogspot.com/2021/03/march-13-14-and-15-bring-big-tornadoes.html" target="_blank">here</a>).</p><p>Tomorrow (March 25, 2021) will likely see another tornado outbreak in the southern Mississippi River Valley into parts of Mississippi, Alabama, Tennessee, and Kentucky. This will probably be similar in scope to the March 17 outbreak with several large long-track tornadoes, so people living in those areas should monitor weather information carefully!</p><p>Yesterday's cold-core event was weak (2 EF0 tornadoes), but fairly classic pattern-wise, occurring in the vicinity of a Pacific cold front intersecting a warm front in the northeast Missouri (MO), west-central Illinois (IL), and southeast Iowa (IA) area east of a closed mid-level low. That was unlike last week's cold-core activity in Kansas, Nebraska, and Missouri (see blog post <a href="http://davieswx.blogspot.com/2021/03/march-13-14-and-15-bring-big-tornadoes.html" target="_blank">here</a>) when the tornadoes occurred along occluded sections of a frontal boundary near the mid-level low, instead of the more common Pacific front/warm front intersection area. </p><p>Here's the 0000 UTC 3/24/21 surface map (7:00 pm CDT 3/23/21) shortly before the tornadoes yesterday:</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiW7odQC8WHzQSDR2WSWw2IVeR-VL6IUES1eVHIfR9tKvA1HCvSEvvn5OSFiZ5mkqM_7lL1Tf93FI1lrJN9buqVBCZoRdiP2JuEwA7u4zVldvLtvdmaODk-3hsebkx1lIBATglEfeu69Yoj/s572/032421sfc0000_anno.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="504" data-original-width="572" height="564" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiW7odQC8WHzQSDR2WSWw2IVeR-VL6IUES1eVHIfR9tKvA1HCvSEvvn5OSFiZ5mkqM_7lL1Tf93FI1lrJN9buqVBCZoRdiP2JuEwA7u4zVldvLtvdmaODk-3hsebkx1lIBATglEfeu69Yoj/w640-h564/032421sfc0000_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>The tornadoes occurred near Rockport, IL (photo at top of this page), and Ft. Madison, IA, marked on the surface map above, close to the Pacific cold fornt / warm front intersection as mentioned earlier, roughly matching the Fig. 16 composite in <a href="https://journals.ametsoc.org/view/journals/wefo/21/6/waf967_1.xml" target="_blank">Davies (2006)</a>.</p><p>The visible satellite photo at the same time (tornadic cell locations at arrows) showed the cloud swirl associated with the mid-level closed low at 700 mb (roughly 10,000 ft MSL) and 500 mb (roughly 18,000 ft MSL):</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiYdEgDnQJkxO1nZkg0INdys9KZmhdxgho7vzN9CrPQyTxw56EFhAXiOX3wC8iO3FEnLQpeh_ujHPAHA2NbVEbk3KNSGTosRuxe0g_HfHHG_nWaiwPXgteTzRJ-LVV9Mb7zgfzBIuGOW_q2/s941/032421sat0001mo-ia-il_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="756" data-original-width="941" height="514" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiYdEgDnQJkxO1nZkg0INdys9KZmhdxgho7vzN9CrPQyTxw56EFhAXiOX3wC8iO3FEnLQpeh_ujHPAHA2NbVEbk3KNSGTosRuxe0g_HfHHG_nWaiwPXgteTzRJ-LVV9Mb7zgfzBIuGOW_q2/w640-h514/032421sat0001mo-ia-il_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>The 12-hr 700 mb forecast from the NAM model morning run on 3/23/21 showed the mid-level low over southwest IA, and a broad area of cold air aloft well below freezing (the blue colors) spreading over the warm sector into western IL: </p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgShQu0PVptH3jPKBFD6s0YC5LIxfYg4nEDeu9GKR3n3sp8N-VilajM-LaNohcjxE_waklhNtUcgyR5K2pmtOa6eNCLkwF_zve-RfXYEieTi8FgguIxlYXwqYYrAkIz3ZEkIZetnKRNpg8o/s625/032421nam700mbT00f12_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="599" data-original-width="625" height="614" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgShQu0PVptH3jPKBFD6s0YC5LIxfYg4nEDeu9GKR3n3sp8N-VilajM-LaNohcjxE_waklhNtUcgyR5K2pmtOa6eNCLkwF_zve-RfXYEieTi8FgguIxlYXwqYYrAkIz3ZEkIZetnKRNpg8o/w640-h614/032421nam700mbT00f12_anno.jpg" width="640" /></a></div><br /><p><br /></p><p>With surface dew points in the mid-50's (deg F) near the warm front, that cold air aloft generated plenty of instability to support storms and some brief tornadoes.</p><p>The 9-hr HRRR model forecasts from mid-morning suggested the location of the Pacific front/warm front intersection fairly well from surface temperatures and winds (1st panel below). Plentiful low-level CAPE (0-3 km, 2nd panel) was also forecast to surround the boundary intersection area and extend northward into southeast IA:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiNy2k0ZbCfH7Gml_NGXS1JPKXK6ql7UpXBX76snnZYw_yiXBLcxpMSdf9dofUHXSrc3f-dOOhwbX8xf9ge6VpTG4izsK9UGijvuXjjaPeBneDJwAHmHOEyTtO3vkVJBPdEM7im3fmjcan5/s1056/032421hrrsfcT-cp300f09_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="596" data-original-width="1056" height="362" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiNy2k0ZbCfH7Gml_NGXS1JPKXK6ql7UpXBX76snnZYw_yiXBLcxpMSdf9dofUHXSrc3f-dOOhwbX8xf9ge6VpTG4izsK9UGijvuXjjaPeBneDJwAHmHOEyTtO3vkVJBPdEM7im3fmjcan5/w640-h362/032421hrrsfcT-cp300f09_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>The low-level CAPE north of the warm front into IA may have been a contributor to the brief tornado with minor damage near Ft. Madison, IA that occurred some distance north of the warm front within a linear feature on radar (not shown), unlike the tornadic supercell near Rockport, IL.</p><p>Back on March 10 (2021), there was a cold-core setting that affected south-central Minnesota that was _not_ tornadic, although a photogenic supercell (not shown) occurred near the warm front in that case. Several people have asked me why that setting did not produce tornadoes, and while I don't have definitive answers, comparing that evening's surface map with yesterday's surface map suggests some clues.</p><p>Notice on the 3/10/21 surface map at 2300 UTC (5:00 pm CST, shown below; location of tornado-warned supercell marked by circled "S") that the warm front was "bulging" much farther northward relative to the surface low:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjdcvAq5TEYhzmFBU8PXCfIHSOvz-LvMU2Ym-b_kHT1OxlDdbs01PKoK0zmVF0FV5jUqNtFY8jtkt4x6BP-KiLYgiY3cMtvKtCihSv1Pto6dUqZhgV_XohYiExcJgv8mDedPPmyksrlFO-d/s558/031021sfc2310_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="477" data-original-width="558" height="548" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjdcvAq5TEYhzmFBU8PXCfIHSOvz-LvMU2Ym-b_kHT1OxlDdbs01PKoK0zmVF0FV5jUqNtFY8jtkt4x6BP-KiLYgiY3cMtvKtCihSv1Pto6dUqZhgV_XohYiExcJgv8mDedPPmyksrlFO-d/w640-h548/031021sfc2310_anno.jpg" width="640" /></a></div><br /><p><br /></p><p>As a result, comparing this map with the surface map earlier from yesterday, there was not much of a "spiraling" wind flow pattern into the surface low. Instead, winds went from a south or south-southeast direction across southeast Minnesota and most of Wisconsin abruptly to a north or north-northeast direction in the area northeast of the surface low. This was different than yesterday's surface setting (see the surface map shown earlier) where winds from the warm sector over Illinois and then flowing into the Iowa surface low (ignoring a few "outflow" locations) backed more gradually across the warm front and farther northwestward, going from southerly to southeasterly to easterly. This more "spiraled" backing wind flow pattern into the surface low may have helped set up a better low-level shear environment for low-level rotation in yesterday's storms near and just north of the warm front.</p><p>I'll make one other observation comparing the two surface maps. In the non-tornadic March 10 case, the temperature contrast across the Minnesota warm front was > 10 deg F in a short distance (say 10-15 miles), which would likely have a detrimental effect on low-levels for tornado potential with the supercell that was crossing the warm front that day. Yesterday, the temperature contrast across the warm front and for miles north of it was rather gradual, only around 5 deg F between west-central IL and southeast IA, and would not have as abrupt an impact on storms crossing the warm frontal area.</p><p>Before I close, I wanted to talk briefly about last week's St. Patrick's Day tornado outbreak in the South. It was well-forecast days in advance by SPC, announced aggressively in media, and there were no deaths and only a few injuries in spite of 30+ tornadoes occurring! The excellent forecasts and media coverage appeared to really contribute to the low injury toll and the lack of deaths. I truly hope the same will be true with tomorrow's expected outbreak in some of the same area.</p><p>Briefly, regarding the 3/17/21 outbreak, here's the morning NAM model forecast at 500 mb valid at mid-afternoon, along with an inset of the NAM 0-1 km energy-helicity index (CAPE and low-level shear combined) for the same time:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgXDFja7YpDHumor1OLhe5UqDutVvv36fG58K5mL78k8n-DHqbMDXX-r7DFmAOQHHlNSTPsdsyc-CJZrIihn9z5sh2mEGDSLiaUv5oBE06QM8zwvnBtAQGn4wA4AYyAE2MUOs3BNbIxdWh7/s720/031721nam500mb-eh121f09pvt_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="619" data-original-width="720" height="550" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgXDFja7YpDHumor1OLhe5UqDutVvv36fG58K5mL78k8n-DHqbMDXX-r7DFmAOQHHlNSTPsdsyc-CJZrIihn9z5sh2mEGDSLiaUv5oBE06QM8zwvnBtAQGn4wA4AYyAE2MUOs3BNbIxdWh7/w640-h550/031721nam500mb-eh121f09pvt_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>The setting was fairly classic, with a strong trough moving eastward across the southern U.S., and "spreading" jet branches providing forcing for generating storms out ahead of the trough where CAPE/shear combinations were strong and very supportive of tornadoes across the broad warm sector in the Dixie states. </p><p>Notice too, that there was yet another "cold-core" setting associated with the same system, this time over southwest MO, where some weak tornadoes occurred.</p><p>And getting back to the Dixie states, below are a couple images of a supercell and long-track tornado (note the horizontal vortex on the second image) that moved across southwest Alabama (see tornado track on inset in image above) at mid-afternoon.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjIpwcvyq0L0sOv1xyH4NZJhGvFGTdV3-PGvYgW3s3Ss8Xmqv15VcJm6PpZSCE89BDh5AHiQD5GB9IiIV4wXLyJNo1tUAYHQoGl3_ZARJt0hz6xVEw4QdDcURatDhQlBSNub_FcrJRdwMWB/s1082/031721swALtor%2526sprcl_jc_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="728" data-original-width="1082" height="430" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjIpwcvyq0L0sOv1xyH4NZJhGvFGTdV3-PGvYgW3s3Ss8Xmqv15VcJm6PpZSCE89BDh5AHiQD5GB9IiIV4wXLyJNo1tUAYHQoGl3_ZARJt0hz6xVEw4QdDcURatDhQlBSNub_FcrJRdwMWB/w640-h430/031721swALtor%2526sprcl_jc_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi3OEGhL9onklWOcTLrRDpQtiNPbyd9Vk4R4BV-gsbEmjQqwQ05ovhOR-QC18AnR8rCvaT1Bx_LucrxisXiGayrsz5DKbGF0ZYNDYa0DlkZhQqowI7haLzdk-S6xlmD9nSl_DsSDph5QvdJ/s606/031721swALtor_be3_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="344" data-original-width="606" height="228" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi3OEGhL9onklWOcTLrRDpQtiNPbyd9Vk4R4BV-gsbEmjQqwQ05ovhOR-QC18AnR8rCvaT1Bx_LucrxisXiGayrsz5DKbGF0ZYNDYa0DlkZhQqowI7haLzdk-S6xlmD9nSl_DsSDph5QvdJ/w400-h228/031721swALtor_be3_anno.jpg" width="400" /></a></div><p>It is a little unusual to be able to see such visible supercell structure in the South.</p><p>I hope people in the Dixie states and the southern Mississippi River Valley/Ohio River Valley areas pay careful attention to weather information tomorrow, March 25, 2021. Stay safe!</p><p>- Jon Davies 3/24/21</p>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com0tag:blogger.com,1999:blog-2399626414603781513.post-75133127672376877222021-03-16T12:59:00.002-07:002021-03-16T13:15:25.802-07:00March 13, 14, and 15 bring big tornadoes and cold-core action to the Plains<p> </p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiBmx97hfWxyU5M3ZU1eHXo5GI99pE-MHVjf3QWbyxMBjsLG8wUrb11fetX8d-QvnjcgG648fAnUok9AP2TeC4ZfT-zLiTB6SkHGnt8WOG0o1rElCO5sM2nYX5kSwj1rxEaNH11QANS2fZR/s674/031321_TXpnhl_tor_kara3_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="331" data-original-width="674" height="314" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiBmx97hfWxyU5M3ZU1eHXo5GI99pE-MHVjf3QWbyxMBjsLG8wUrb11fetX8d-QvnjcgG648fAnUok9AP2TeC4ZfT-zLiTB6SkHGnt8WOG0o1rElCO5sM2nYX5kSwj1rxEaNH11QANS2fZR/w640-h314/031321_TXpnhl_tor_kara3_anno.jpg" width="640" /></a></div><br /><p></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi0I8fpvc3IVoXtH9CwGz_t_xjLmn5DrTk8bUFOY-j5n9_hxaZYCk2ceZHbggOXJhbFhI5IvqjRblljxX6A65JprqKWBKNCM1sSHwDLIYsQnx9GH4bNBsZY_uQyX81IF-3ZLsF0BDWsDDs5/s706/031321rdrsrv_twintors_2133_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="706" data-original-width="479" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi0I8fpvc3IVoXtH9CwGz_t_xjLmn5DrTk8bUFOY-j5n9_hxaZYCk2ceZHbggOXJhbFhI5IvqjRblljxX6A65JprqKWBKNCM1sSHwDLIYsQnx9GH4bNBsZY_uQyX81IF-3ZLsF0BDWsDDs5/w434-h640/031321rdrsrv_twintors_2133_anno.jpg" width="434" /></a></div><div class="separator" style="clear: both; text-align: center;"><br /></div><p>Friday, March 12 through Monday, March 15, 2021 saw tornado activity really ramp up in the Central Plains. There were no deaths or injuries reported, as the biggest day (Saturday, March 13) was well-forecast and warned.</p><p>Over 10 tornadoes occured on March 13 in the central and southern Texas (TX) panhandle, including the twin large tornadoes pictured above from the same supercell near the town of Happy, along with a storm-relative velocity image at roughly the same time showing the two mesocyclones side by side. The tornado and mesocyclone labeled "1" above generated a tornado rated EF2 on the ground for 17 miles according to NWS Amarillo (had the tornado hit a town, the EF rating would likely be higher).</p><p>Farther east, according to radar, it appeared there were also two tornadoes on the ground simultaneously at times with the Happy, TX supercell according to radar (not shown). But these were not photographed as the storm became increasingly wrapped in rain and the radar circulations occurred in difficult spotter/chaser terrain northeast of the Palo Duro Canyon State Park. It doesn't appear that there were any tornado mergers, but that's not entirely clear, and there were also times when multiple mesocyclones appeared to be interacting with each other (not shown).</p><p>The following two days, other localized tornadoes occurred in northwest Kansas (KS) and southwest Nebraska (NE), including the "white" landspout tornado pictured below (1st photo) west of Trenton, NE on Sunday March 14, and a tornado near Stilwell, KS, south of Kansas City (2nd photo) where some minor damage occurred (rated EF0):</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgiHIRzjaAhHKGRZKV3SNRvAA38gp4RWFRMpdZSGpbDfCv0hyBKC1KuZsdJadqadHVODV0R-5pgRVHhmNnPVRodYF3P8wSxTOG2bbbQZzqjR9gllx5hqgas3aa3vxDobG9calXmYAAl2Gqd/s501/031421swNElndspt_ms_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="340" data-original-width="501" height="271" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgiHIRzjaAhHKGRZKV3SNRvAA38gp4RWFRMpdZSGpbDfCv0hyBKC1KuZsdJadqadHVODV0R-5pgRVHhmNnPVRodYF3P8wSxTOG2bbbQZzqjR9gllx5hqgas3aa3vxDobG9calXmYAAl2Gqd/w400-h271/031421swNElndspt_ms_anno.jpg" width="400" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhIyT3e4iNURtMnCcXISVbxO0jKk1zI81afmY0jgtnqmSGKy3EM91CGh3dQ0cVITbmjHwsSv_eVrzvsNkfRhStF8qfjce97A6w3DL8c3ZaEpcmNSyxMcVSFO8S4HvTT_GuiqnbBcNoEQ5ms/s612/031521ecKStor_sp_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="350" data-original-width="612" height="229" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhIyT3e4iNURtMnCcXISVbxO0jKk1zI81afmY0jgtnqmSGKy3EM91CGh3dQ0cVITbmjHwsSv_eVrzvsNkfRhStF8qfjce97A6w3DL8c3ZaEpcmNSyxMcVSFO8S4HvTT_GuiqnbBcNoEQ5ms/w400-h229/031521ecKStor_sp_anno.jpg" width="400" /></a></div><p>I'll briefly touch on the meteorological setting for March 13, March 14, and March 15, as these days involved a closed 500 mb low within a large mid-level trough moving slowly northeastward from the southwestern U.S. On March 13, the 500 mb low was too far to the west to be directly involved in the Texas tornado outbreak, but on the subsequent two days, the cold-core low aloft had a direct impact on tornadoes occurring in rather marginal settings.</p><p>Below is a visible satellite image at mid-afternoon on March 13, with surface weather map features drawn in, and the location of the 500 mb low well to the west:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEji4f_DztHUEOSAsQwI5i8UOyfkKortbOumlPNqfWI9zpOj6vVWXTKn5Jinm1QpayI9hGSyePpVhsVOj7lSQ8A7JEC2xpqx41KSGjaQcKZUccGg3zRMSOJaimbBDDvqNvcFS5Pi09_GD_DL/s558/031321satsfc2101_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="455" data-original-width="558" height="522" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEji4f_DztHUEOSAsQwI5i8UOyfkKortbOumlPNqfWI9zpOj6vVWXTKn5Jinm1QpayI9hGSyePpVhsVOj7lSQ8A7JEC2xpqx41KSGjaQcKZUccGg3zRMSOJaimbBDDvqNvcFS5Pi09_GD_DL/w640-h522/031321satsfc2101_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>The tornadic supercells occurred in the warm sector ahead of a Pacific cold front and south of a warm front over the TX panhandle, including the Happy, TX supercell (labeled with arrow). Below are SPC mesoanalysis images of two composite tornado parameters, suggesting how favorable for supercell tornadoes the environment was over the panhandle at 2200 UTC (4:00 pm CST) while tornadoes were ongoing near and east of Happy, TX:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh1EHIT_7kjMQAv09b7JJjGteqiNv-_BS3FudpXpvgmxED62CXCCWSQpyefikYoOAUAMadmlq7PDv5vAX6CVuioKDhXq4vsB1eFNjF6JtYZH893Fne7-QOayYT8Q-6yArMZFoKFHHkUtJlj/s863/031321spc_stpc-tehi22_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="547" data-original-width="863" height="406" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh1EHIT_7kjMQAv09b7JJjGteqiNv-_BS3FudpXpvgmxED62CXCCWSQpyefikYoOAUAMadmlq7PDv5vAX6CVuioKDhXq4vsB1eFNjF6JtYZH893Fne7-QOayYT8Q-6yArMZFoKFHHkUtJlj/w640-h406/031321spc_stpc-tehi22_anno.jpg" width="640" /></a></div><br /><p><br /></p><p>And here's an analysis sounding from the RAP model at Plainview TX (south of the Happy, TX supercell) at 2100 (3:00 pm CST) at about the time the outbreak started:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhnCSuLncz-TmUzm5AXELcTk6KJJbSWNL9LD0Bk-dxUpIgLvIhgKBTxOohaI9K3aktk5HUvJ4Iyz1cAfQuzGuiNo1vwUhnRo8mnQ_D7H21ZGoCK8zI3loLpcybNbfK8xfLkxyWiRKTnLNhZ/s1196/031321pvw21rapa_cod_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="784" data-original-width="1196" height="420" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhnCSuLncz-TmUzm5AXELcTk6KJJbSWNL9LD0Bk-dxUpIgLvIhgKBTxOohaI9K3aktk5HUvJ4Iyz1cAfQuzGuiNo1vwUhnRo8mnQ_D7H21ZGoCK8zI3loLpcybNbfK8xfLkxyWiRKTnLNhZ/w640-h420/031321pvw21rapa_cod_anno.jpg" width="640" /></a></div><br /><p><br /></p><p>Notice that parameters such as mlCAPE (> 2000 J/kg), 0-1 km storm-relative helicity (SRH > 250 m2/s2), surface to 6 km shear (> 70 kt), and 0-3 km mlCAPE (> 150 J/kg) were all highly favorable in this environment for supercells capable of generating strong tornadoes.</p><p>The next day (Sunday, March 14), satellite with surface features (below) showed that the 500 mb low had moved to eastern Colorado (CO), where a blizzard dumping over 2 feet of snow was in progress over northern CO and southeast Wyoming. The surface low had also evolved northward to eastern CO, with a massive dry slot/clear slot punching northward across most of Kansas with the 500 mb low, while the Pacific cold front had advanced eastward:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQdlxRGKBpwjgOAMtSw0tkXy9lXvch1HU5_wAIpj-5yRSHcW_ZvYClrst8UbhyHB9DvknbxTjLfin68WG0TX1HAqDA3lE4ehU_4F816C3kz0rAPWsr8KFZEhWFVIsGNZv7LnwkxGwCzSKV/s497/031421satsfc1901_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="497" data-original-width="492" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQdlxRGKBpwjgOAMtSw0tkXy9lXvch1HU5_wAIpj-5yRSHcW_ZvYClrst8UbhyHB9DvknbxTjLfin68WG0TX1HAqDA3lE4ehU_4F816C3kz0rAPWsr8KFZEhWFVIsGNZv7LnwkxGwCzSKV/w634-h640/031421satsfc1901_anno.jpg" width="634" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>Along the occluded front extending northeastward from the CO surface low, the wind shift along the boundary combined with surface heating and CAPE (from the cold air aloft with the mid-level low) to help produce a couple of brief landspout tornadoes at early afternoon, including the Nebraska EF0 tornado pictured earlier.</p><p>An SPC image of 0-3 km mlCAPE and surface vorticity at 1900 UTC (2:00 pm CDT) showed very well the low-level CAPE (in red) overlapping the west-east boundary (blue surface vorticity lines) over northwest KS and southwest NE:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgWflV_NjOD7M4uOfm8Fxuw5XHyW0-TQyTrC76FprUiXcCRVO5exPlR8XQmX4mxgP0ceFX2K3-xUhj6IPFRRsnNyK9lBZW3bNqoIki1CboOmOnWwvrfDBJ0e4Bg-23aQU22buGXdYLxyR84/s528/031421spccp319_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="476" data-original-width="528" height="360" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgWflV_NjOD7M4uOfm8Fxuw5XHyW0-TQyTrC76FprUiXcCRVO5exPlR8XQmX4mxgP0ceFX2K3-xUhj6IPFRRsnNyK9lBZW3bNqoIki1CboOmOnWwvrfDBJ0e4Bg-23aQU22buGXdYLxyR84/w400-h360/031421spccp319_anno.jpg" width="400" /></a></div><p>These are ingredients that can generate non-supercell tornadoes such as landspouts when low-topped storm updrafts from CAPE and heating phase properly with the boundary so that vertical vorticity along the wind shift can be stretched upward.</p><p>Here's a RAP model 1-hr forecast sounding near Trenton, NE shortly before the brief NE tornado pictured earlier -- notice how the CAPE is relatively small but bunched low in the atmosphere, typical of tornado settings near 500 mb lows:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjC4Ewhcbl7VivZsN-O-uB4ywlnD6wfaj_49x0y4fFnsgZUOg9OjAaDNKfAF6P02CAewFEYysyKz51LuBB69zVyB2LalrTXe8Ydl_-DPxbU-T65CtqnNlaRP42KgSLndTFT5EDY9ZFtsU4H/s1194/031421atwoodKS-trentonNE19f01_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="787" data-original-width="1194" height="422" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjC4Ewhcbl7VivZsN-O-uB4ywlnD6wfaj_49x0y4fFnsgZUOg9OjAaDNKfAF6P02CAewFEYysyKz51LuBB69zVyB2LalrTXe8Ydl_-DPxbU-T65CtqnNlaRP42KgSLndTFT5EDY9ZFtsU4H/w640-h422/031421atwoodKS-trentonNE19f01_anno.jpg" width="640" /></a></div><br /><p><br /></p><p>And here's an image showing the crisp low-topped storms looking north from KS into NE associated with this occluded front and cold-core setting:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjq2QERmT3J5D3p1COTnZj82G7keabd1K9pICwtxeUhdjRKaFYfAilViOD4Af_t42HboWAtqe4AAZNC_L6aRIBd_YxWfkMuc5AUJuFfQIBUa_9sXLt1eDj3MVQpBJOtoDxAFENqX2UXR4bN/s1022/031421nwKSstms_jt2_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="606" data-original-width="1022" height="380" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjq2QERmT3J5D3p1COTnZj82G7keabd1K9pICwtxeUhdjRKaFYfAilViOD4Af_t42HboWAtqe4AAZNC_L6aRIBd_YxWfkMuc5AUJuFfQIBUa_9sXLt1eDj3MVQpBJOtoDxAFENqX2UXR4bN/w640-h380/031421nwKSstms_jt2_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>Last, here's the satellite/surface setting on Monday, March 15 between 2000 UTC and 2100 UTC (3:00-4:00 pm CDT) over the KS-Missouri(MO) area:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgCU26q4UpFG8-vUfpkfDN4cqjMkR5X36fGWNl0zzaVg9hgDt9rokPvAsm7TeiwLDWCYKPrfolsaijF7vfGbJiXfa5dyEFB2_rCByCOM6jxcr-jhqqLBAn2vlGoKgCGzgR90z8tbk6ZcXYx/s502/031521satsfc2036_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="491" data-original-width="502" height="626" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgCU26q4UpFG8-vUfpkfDN4cqjMkR5X36fGWNl0zzaVg9hgDt9rokPvAsm7TeiwLDWCYKPrfolsaijF7vfGbJiXfa5dyEFB2_rCByCOM6jxcr-jhqqLBAn2vlGoKgCGzgR90z8tbk6ZcXYx/w640-h626/031521satsfc2036_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>The 500 mb low had "split" or evolved into two centers, with one drifting east across Kansas and generating a surface low over northeast KS near the stalled occluded front. With all the cold air aloft associated with the 500 mb low and the west-east boundary near Kansas City, the stage was set for a couple more brief tornadoes, including the one pictured earlier near Stilwell, KS.</p><p>The SPC depiction of low-level CAPE and surface vorticity at 2100 UTC showed a setting similar to the day before (low-level CAPE overlapping the boundary ), except this time near Kansas City:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhOs-Je9-CnJN9JhMqeX7QaxZkzXhLuZQUFcMX9QQryLkrbX5Gl651AXZOqJ8kVfu6SwIqJzsOn55ZA_HSU7QenmppDoRjEwkqiOnRXZdCwDwr2jJCedAv93i9kwZnvkisXu13dHeTKztkB/s520/031521spccp321_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="476" data-original-width="520" height="366" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhOs-Je9-CnJN9JhMqeX7QaxZkzXhLuZQUFcMX9QQryLkrbX5Gl651AXZOqJ8kVfu6SwIqJzsOn55ZA_HSU7QenmppDoRjEwkqiOnRXZdCwDwr2jJCedAv93i9kwZnvkisXu13dHeTKztkB/w400-h366/031521spccp321_anno.jpg" width="400" /></a></div><p>And here's a RAP model 1-hr forecast sounding at Harrisonville, Missouri, shortly before the tornado at Stilwell, KS just west across the KS-MO border:</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh_kNNjPK907D8hge_hZmFa6mxfC-TWTr-9x9TlKwU_zsjUXXQejH6mJl1oG5k0Sr1pE73RogBFF3FHj2uCIJAzGwYNPhDsVM8FGxdL8Ayz7Zp82J8HYjDAHKxHGDmWa0hRVaoxQsJSnKsr/s1194/031521lry21rapa_cod_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="786" data-original-width="1194" height="422" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh_kNNjPK907D8hge_hZmFa6mxfC-TWTr-9x9TlKwU_zsjUXXQejH6mJl1oG5k0Sr1pE73RogBFF3FHj2uCIJAzGwYNPhDsVM8FGxdL8Ayz7Zp82J8HYjDAHKxHGDmWa0hRVaoxQsJSnKsr/w640-h422/031521lry21rapa_cod_anno.jpg" width="640" /></a></div>With a somewhat more clockwise-curving hodograph, the Stilwell storm appeared more supercellular on radar (not shown), but the components of low-level CAPE and the boundary were also likely significant contributors to the tornado in this occluded front and cold-core setting.<p>In the March 13, 2021 Texas case, parameters and ingredients were strong within the warm sector away from pre-existing fronts and boundaries to help generate several classic-type supercell tornadoes. But on March 14 and 15 as the 500 mb low moved slowly out into the Plains, the tornadoes were more a result of low-topped storms interacting with an occluded front, where the boundary was a key factor.</p><p>It is interesting to note that the Texas twin tornadoes pictured at the top of this article occurred 31 years to the day after the twin Hesston-Goessel KS tornadoes that went on to merge together into an EF5 tornado.</p><p>And I must note that St Patrick's Day 2021 (tomorrow) will likely see a significant outbreak of severe weather and tornadoes in the South over the Arkansas-Louisiana-Mississippi-Alabama area. I hope everyone in those areas stays informed and up-to-date on the weather.. stay safe!</p><p>- Jon Davies 3/16/21</p>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com0tag:blogger.com,1999:blog-2399626414603781513.post-84949749683312624122021-02-22T06:32:00.020-08:002021-02-22T07:56:00.154-08:00A difficult tornado to forecast - 2021's 2nd deadly tornado on February 15 kills 3 people in North Carolina<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiCad5stxOKnYhMj00JpW2HdEb64nknVCY50NLdBtLpThsnf0T_wfmKgfSh9tKitlxmygYt4HtHd6RxOeiWJD-eLYT0W2V_cxNhcQRml07uduK_HMkG3XfeiOVhhLVfSDsUbpaWZ9Gbs_P3/s607/021621seNCsprcl_ae_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="352" data-original-width="607" height="233" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiCad5stxOKnYhMj00JpW2HdEb64nknVCY50NLdBtLpThsnf0T_wfmKgfSh9tKitlxmygYt4HtHd6RxOeiWJD-eLYT0W2V_cxNhcQRml07uduK_HMkG3XfeiOVhhLVfSDsUbpaWZ9Gbs_P3/w400-h233/021621seNCsprcl_ae_anno.jpg" width="400" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi8LXQCbMmaLSdq7faWju1BRiXKXuFmimS2bwvJmVdahK27QqZv42koPwjLC0WRlQzXxb7WhU_x1oeFIjkg6UCSHxm5q6cTnctcLafZEFMVeZ2t2eUfLe5eRjHW1FgqGJ1Jjki2cavADAMp/s932/021621seNCtordmg_nws_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="625" data-original-width="932" height="269" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi8LXQCbMmaLSdq7faWju1BRiXKXuFmimS2bwvJmVdahK27QqZv42koPwjLC0WRlQzXxb7WhU_x1oeFIjkg6UCSHxm5q6cTnctcLafZEFMVeZ2t2eUfLe5eRjHW1FgqGJ1Jjki2cavADAMp/w400-h269/021621seNCtordmg_nws_anno.jpg" width="400" /></a></div><br />Last Monday's EF3 tornado near the coast of southeast North Carolina (north of Sunset Beach NC) killed 3 and injured 10. Because it occurred at night (between 11:30 pm and midnight EST), there were no photos of the tornado, but a storm chaser managed an image of the tornadic supercell (top photo above) off the coast east of Myrtle Beach, South Carolina (SC) around 30 minutes before it struck on land just north of the NC-SC border. The 2nd photo above shows some of the impressive damage (see <a href="https://www.weather.gov/ilm/BrunswickTornadoFeb2021" target="_blank">this page on the tornado</a> from NWS Wilmington NC).<p></p><p>There was no tornado watch in NC ahead of the storm, and a tornado warning was not issued for Brunswick County where the tornado occurred until 5 minutes after it developed. That's because it was far from an obvious forecast setting, which is worth posting about here. The environment was also evolving rapidly, and the tornado developed fast on radar (not shown) when the supercell moved on land.</p><p>A forecast and nowcast problem in this case was that surface-based (sb) instability at 11:00 pm EST 2/16/21 (0400 UTC) appeared to be well off shore from the Carolinas (see sbCAPE on the first panel below from the SPC mesoanalysis):</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhUBkajhaY9hyDrzD3rYgUAy3ZCdlPH-ZRV7kn2RDjfxpvy_ANG01DXBrh40ik1shLLWFgSMdrBocQuWslv-kkC028T9-hWVcyJnCCMBWB_ooh2-9ETKvVO6tTnI1QidCCkw3ajxswisPds/s1282/021621spc-sbcpe-mlcpe-stpc04_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="600" data-original-width="1282" height="301" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhUBkajhaY9hyDrzD3rYgUAy3ZCdlPH-ZRV7kn2RDjfxpvy_ANG01DXBrh40ik1shLLWFgSMdrBocQuWslv-kkC028T9-hWVcyJnCCMBWB_ooh2-9ETKvVO6tTnI1QidCCkw3ajxswisPds/w640-h301/021621spc-sbcpe-mlcpe-stpc04_anno.jpg" width="640" /></a></div><br /><p><br /></p><p>When there is no surface-based instability within a severe weather threat area, storms that do occur are considered to be "elevated", meaning that the instability (CAPE) supporting the storms comes from lifted air located somewhere above the ground. Because tornadoes by definition occur at the ground (different from a "funnel" aloft), tornadoes are generally not expected in such elevated settings because air at the ground is typically too stable to support tornadoes.</p><p>This "elevated" factor affected composite tornado forecast parameters such as the effective-layer significant tornado parameter (STP), shown in the 3rd panel of the SPC graphic above, where effective STP was near 0 along the coast of the Carolinas, a result of this apparently "elevated" environment. </p><p>However, looking at mixed-layer CAPE (mlCAPE, 2nd panel in the graphic above), which uses an average of the temperature and moisture properties within the lowest 1 km above ground, notice that some CAPE (around 500 J/kg) was present right along the northeast SC and southeast NC coast at 0400 UTC near Sunset Beach (black square dot). This is because there was significant moisture and increased temperature flowing northward above a shallow stable layer at the ground. A RAP model sounding profile at Southport, NC (roughly 25 miles east of Sunset Beach), modified using a 0430 UTC temperature and dew point surface observation of 64 deg F and 64 deg F, showed this:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh3eciMIWw8xvUZh8NQmG6CxPhZa3uOtPDCyfnFR6Cpf4Pyk5PWlitry3l4pshRiCAm_-WZ4gfMEkeBBFjU_EWquh73Cd7JDPkqAvyBJcYIEfEgQcHhqFfwsw8BqRhqWhGOOdFnNaWCJHt3/s1190/021621sut04rapf01_cod_mod_anno2.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="786" data-original-width="1190" height="422" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh3eciMIWw8xvUZh8NQmG6CxPhZa3uOtPDCyfnFR6Cpf4Pyk5PWlitry3l4pshRiCAm_-WZ4gfMEkeBBFjU_EWquh73Cd7JDPkqAvyBJcYIEfEgQcHhqFfwsw8BqRhqWhGOOdFnNaWCJHt3/w640-h422/021621sut04rapf01_cod_mod_anno2.jpg" width="640" /></a></div><br /><p><br /></p><p>Notice that the yellow dashed lifting curve at left on the graphic above (representing a surface-based lifted parcel of air) generated _no_ CAPE, suggesting an "elevated" environment. But in contrast, the yellow dashed lifting curve at right (representing a lifted parcel of air from around 0.3 km above ground), did indicate notable CAPE, as seen by the red mlCAPE area on the sounding. </p><p>In other words, significantly unstable air was present less than 1000 ft above the ground, just above the very shallow stable layer. It was this instability, combined with large low-level wind shear (storm-relative helicity or SRH of 350-400 m2/s2) near a warm front that helped support low-level rotation and a tornado in the supercell that moved on shore near Sunset Beach NC. Apart from the shallow stable layer, the environment was a small instability and large wind shear setting often typical of southeast U.S. tornadoes in the cool season.</p><p>Warm fronts with significant combinations of CAPE and SRH along and near them are recognized in forecasting as potentially supportive of tornadoes with supercells that move along with or across them. The surface map below at 11:00 pm EST (0400 UTC) shows that, indeed, a warm front was present moving northward near the NC-SC border along the coast:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj5VCmQtd564bFrF9oJG8g01CUMQouB-iTvTcepBKXn352Lw5Tb5m0ATCDMH_jkqOlrb133VN4ehvKrduV8b3uUONERSuPJPPPjDD_CDjlFuUl333rDRuQfHTBUGgg3hP1X7ZrjsGBUc-TU/s511/021621sfc0358_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="511" data-original-width="504" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj5VCmQtd564bFrF9oJG8g01CUMQouB-iTvTcepBKXn352Lw5Tb5m0ATCDMH_jkqOlrb133VN4ehvKrduV8b3uUONERSuPJPPPjDD_CDjlFuUl333rDRuQfHTBUGgg3hP1X7ZrjsGBUc-TU/w395-h400/021621sfc0358_anno.jpg" width="395" /></a></div><p>Also, the SPC graphic below at 0400 UTC showed that some low-level instability (mlCAPE in the lowest 3 km above ground) and large low-level wind shear (SRH in the lowest 1 km above ground) were both present in a small corridor along the NC-SC coast, near the warm front seen on the surface map above:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj__LwrjxiIY_MMK2Hie9-9TqLFbPJbmvYCmRNuEgO3IF08w9nHr91f9CjJFlw6p7IPtldiZxxenbC_uiZBIfyo4fzz0wH4NkjH90jVvk0RneNro3-mhBM8f5qSYcblpXDVSkOR8tyLMMNe/s1035/021621spc-cp3-srh1_04_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="622" data-original-width="1035" height="384" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj__LwrjxiIY_MMK2Hie9-9TqLFbPJbmvYCmRNuEgO3IF08w9nHr91f9CjJFlw6p7IPtldiZxxenbC_uiZBIfyo4fzz0wH4NkjH90jVvk0RneNro3-mhBM8f5qSYcblpXDVSkOR8tyLMMNe/w640-h384/021621spc-cp3-srh1_04_anno.jpg" width="640" /></a></div><br /><p><br /></p><p>Although these ingredients were present only in a narrow strip along the coast, they apparently were enough to support the deadly supercell tornado near the warm front and the coast. But the shallow stable layer near the ground discussed earlier masked this potential by suggesting an elevated environment along the same warm front that was actually not as significantly "elevated" as it looked at first glance. This was due to the shallowness of the stable layer along the coast and the warmth/moisture flowing northward just above the ground.</p><p>Radar below shows the supercell just off shore at 10:00 pm EST (0300 UTC) that eventually moved on shore in NC near Sunset Beach around 11:30 pm EST (0430 UTC), interacting with the surface warm front and CAPE/wind shear just above the ground to produce the deadly tornado that lasted until midnight EST:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgqVbY366Q68_BSjXulqk79I3x-hgAPWFukVGpIKEKdNC7g7TfJvAaOb-cG_w2mAOeaOcSO5a9oRcSHlf0nfCgtrAh4Mn-cT5kj1U3dPGLqeV763s31SCMmjq8Fm81ztQpYlVZmyBC8wx6o/s993/021621rdrr0300-0440sc-nc_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="600" data-original-width="993" height="386" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgqVbY366Q68_BSjXulqk79I3x-hgAPWFukVGpIKEKdNC7g7TfJvAaOb-cG_w2mAOeaOcSO5a9oRcSHlf0nfCgtrAh4Mn-cT5kj1U3dPGLqeV763s31SCMmjq8Fm81ztQpYlVZmyBC8wx6o/w640-h386/021621rdrr0300-0440sc-nc_anno.jpg" width="640" /></a></div><br /><p><br /></p><p>As the supercell moved farther inland away from the coast, the low-level stable layer apparently became too deep, eliminating near-surface CAPE, and there were no other tornadoes over eastern NC.</p><p>Forecast maps from the morning of February 15 did hint that there might be ingredients for a marginal possibility of tornadoes near the SC-NC coast, but that potential was certainly not very evident. Below are the NAM model 500 mb forecast for mid to late evening, and a 2-panel NAM model forecast of mlCAPE and 0-1 km SRH:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjGwB9uziWnoYQRHbjXmuOCIGlx66HohxrE36do0IWBOR88GUCDxSSXt4KbwK2T1GrxgFiNotfiWxLhe9cTDHP4MUZO50F2YmOpEmfqU_3ASgOEpkCR6KzT9Meni8fQpXTu0DsstXy-Fnk8/s683/021621nam500mb03f15pvt_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="683" data-original-width="622" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjGwB9uziWnoYQRHbjXmuOCIGlx66HohxrE36do0IWBOR88GUCDxSSXt4KbwK2T1GrxgFiNotfiWxLhe9cTDHP4MUZO50F2YmOpEmfqU_3ASgOEpkCR6KzT9Meni8fQpXTu0DsstXy-Fnk8/w582-h640/021621nam500mb03f15pvt_anno.jpg" width="582" /></a></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgq44I4rYUqXfQmLTP3Ocfx-Df0EwRwiczj1uL-XTCkt7dwtTCFbsZOjLQLoglI6iwnM97Y_Qs27JOWtic0urrKQNUOmijv8pPf4sboZmpbCuBFqwsN2dcoKhqgQbTq0O1_JjmiIQTmWGBu/s937/021621nam_mlcpe-srh1_03f15pvt_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="576" data-original-width="937" height="394" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgq44I4rYUqXfQmLTP3Ocfx-Df0EwRwiczj1uL-XTCkt7dwtTCFbsZOjLQLoglI6iwnM97Y_Qs27JOWtic0urrKQNUOmijv8pPf4sboZmpbCuBFqwsN2dcoKhqgQbTq0O1_JjmiIQTmWGBu/w640-h394/021621nam_mlcpe-srh1_03f15pvt_anno.jpg" width="640" /></a></div><br /><p><br /></p><p>At 500 mb (roughly 18,000 ft above sea level), a large trough was moving through the mid-section of the U.S., bringing with it last week's news-making frigid arctic cold to the central Plains and particularly Texas. Ahead of this trough, a spreading jet branch pattern was over the southeastern US providing lift through diffluence, and at mid-evening some mlCAPE was forecast just touching the NC-SC coast, barely overlapping large 0-1 km SRH near the afforementioned warm front. This narrow juxtaposition of ingredients was a hint of sorts, but only a small one and nothing that appeared very threatening or alarming for the evening forecast environment. </p><p>Earlier on 2/15/21 (not shown), an EF2 tornado struck southwest Georgia at mid-afternoon, also located near the same warm front that traveled rapidly during the day from the Florida Panhandle all the way to the Carolinas. The warm front in essence outran the instability axis as it moved across eastern Georgia and into South Carolina during the late afternoon and early evening, but then encountered a new fetch of instability again by late evening coming off the Atlantic Ocean along the coast of the Carolinas when the deadly tornado occurred.</p><p>Warm fronts are a feature to watch carefully in tornado forecasting, particularly fast-moving ones as in this case. Often the environment in the immediate vicinity of the warm front may appear "elevated" with a layer of cool surface air north of the front. But if the front is moving <i><u>rapidly</u></i>, the environment may be changing rapidly as well with warm/moist near-surface air flowing quickly northward, producing CAPE where there was none an hour or two earlier. </p><p>This case also emphasizes that when a cool near-surface layer is very shallow along a warm front, sufficient instability may be present to support tornadoes even if the setting appears "elevated" at first glance. Rapidly-moving warm fronts can really modify and change a local environment quickly.</p><p>- Jon Davies 2/22/21 </p><div><br /></div>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com0tag:blogger.com,1999:blog-2399626414603781513.post-3408167234993753622021-01-29T11:48:00.018-08:002021-01-29T12:49:31.109-08:00First strong tornado of 2021 kills 1 and injures 30 near Birmingham, Alabama on January 25th<p>It's been awhile since I've done a write up about a weather event. Frankly, there has been so much going on in our nation that it's been very hard to focus on weather. </p><p>The first tornado death of 2021 occurred this week on Monday, January 25 in Alabama (AL) where an EF3 tornado struck Fultondale, a northern suburb of Birmingham, around 10:43 pm CST (0443 UTC 1/26/21). There were also 30 injuries. The first image from video below shows one of the huge power flashes in northern Birmingham as the tornado moved through, and the second image shows some of the damage:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhumhskzDrxv_DLqFuh5l6S64ne2LvtQzhIHUgpGiefvDOdOcn6ZN8q83LnmAcC3bfQhngYzbliocQkaZURDcb5Asem5pN9bthVQLLfPCEuUEiS3dRflOLyMtwAvnMqOPmgP2rvqyTvyd6_/s503/012621cALtor_rj_pwrflsh_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="292" data-original-width="503" height="233" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhumhskzDrxv_DLqFuh5l6S64ne2LvtQzhIHUgpGiefvDOdOcn6ZN8q83LnmAcC3bfQhngYzbliocQkaZURDcb5Asem5pN9bthVQLLfPCEuUEiS3dRflOLyMtwAvnMqOPmgP2rvqyTvyd6_/w400-h233/012621cALtor_rj_pwrflsh_anno.jpg" width="400" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjMKfAv-iv0eQoB504fDn7v8dnNt4OfUCvVRCMWXJLZj0oc1GPqLXsFLErqmVU2SAOKd0DUiRvsq8ZDliSep-agUpZcQzYHT8ujubjyHtCRE6ZN4hKqV-Q54bJ0Wq-1COpFfZhAUQvz64IQ/s524/012621cALtordmg_ss2_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="331" data-original-width="524" height="253" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjMKfAv-iv0eQoB504fDn7v8dnNt4OfUCvVRCMWXJLZj0oc1GPqLXsFLErqmVU2SAOKd0DUiRvsq8ZDliSep-agUpZcQzYHT8ujubjyHtCRE6ZN4hKqV-Q54bJ0Wq-1COpFfZhAUQvz64IQ/w400-h253/012621cALtordmg_ss2_anno.jpg" width="400" /></a></div><p>Here's a quick look at the meteorological setting:</p><p>It took a long time for the cell that produced the Fultondale tornado to get its act together. As you can see on the radar images below, the storm originated in Louisiana at mid-afternoon on the 25th, taking roughly 7 hours to get around to producing the deadly tornado in AL that evening:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhY7Zntio5izsSVUIAOC4r0WIWZUyXldkLfcbd8gOSL7MN-44eZ0mXspiMS3cTupy-zvzv0sAmO4GQZqEA4-j41eGBgHe8f6sqCuTrV4Z0k7tz-Hgyel-oDp0zAvDMIdnYblu6sbHq_ddWS/s1393/012621rdrr2135-0100-0430ms-al_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="673" data-original-width="1393" height="310" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhY7Zntio5izsSVUIAOC4r0WIWZUyXldkLfcbd8gOSL7MN-44eZ0mXspiMS3cTupy-zvzv0sAmO4GQZqEA4-j41eGBgHe8f6sqCuTrV4Z0k7tz-Hgyel-oDp0zAvDMIdnYblu6sbHq_ddWS/w640-h310/012621rdrr2135-0100-0430ms-al_anno.jpg" width="640" /></a></div><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>It is noteworthy that, apart from the death and injuries near Birmingham AL, the same supercell also killed one person and injured two others from strong non-tornadic winds in central Mississippi (MS) around 6:40 pm CST (0040 UTC 1/26/21 - see middle panel above). It's easy to forget that, in addition to tornadoes, strong thunderstorm winds can kill people, too.</p><p>Also worth noting is the thermal boundary from central MS into central AL (red-blue dashed line in middle panel above) that was in place due to storms that had already tracked east-northeast across this area (this boundary was also evident on surface maps, not shown). Plenty of research over the years indicates that tornadoes like such boundaries because of the focus of convergence and the energy from contrasting temperatures and wind shear that can help supercell storms spin up tornadoes. This particular boundary may have helped intensify the deadly supercell that eventually produced the tornado near Birmingham.</p><p>The NAM model forecast from the morning of 1/25/21 suggested that tornadoes might be possible during the evening. Below, the 300 mb forecast for mid-evening (300 mb is the best level in this case for showing the jet stream pattern and branches; see thick white lines and arrows) depicts the spreading wind pattern and associated broad lift across the southeastern U.S. Also shown (inset) are combined instability and low-level wind shear via the 0-1 km energy-helicity index (EHI), indicating a potentially favorable area for tornadoes with storms just north of the southern jet stream branch across MS and AL:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgOuBirONzyqs2LVVjNPg3bSvJbcGMtIMbqYZWoCPdEahyI8OXnv_xsoV_MrMkFRmnEo4VEre6cGZINR328ab4238kzdclkLoBhD0oeUnpl5KLihaWKFBEZ_8aof9dYiwKbhZUALSZYIKNV/s746/012621nam300mb-eh103f15pvt_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="529" data-original-width="746" height="454" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgOuBirONzyqs2LVVjNPg3bSvJbcGMtIMbqYZWoCPdEahyI8OXnv_xsoV_MrMkFRmnEo4VEre6cGZINR328ab4238kzdclkLoBhD0oeUnpl5KLihaWKFBEZ_8aof9dYiwKbhZUALSZYIKNV/w640-h454/012621nam300mb-eh103f15pvt_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>The EHI values above from southwest MS to central AL at mid-evening suggests that the supercell moving across MS into AL during the evening (see earlier radar images) had a long residence time moving through a potentially favorable environment for tornadoes. This being the cool season, the supercell may have needed this broad warm sector environment to eventually produce the tornado near Birmingham. And, as noted earlier, the storm was moving along and parallel to a thermal boundary.</p><p>A closer look at the environment using SPC mesoanalysis graphics (below) suggests that the environment along the boundary as the evening progressed was more favorable for tornadoes over AL. The 0-1 km storm-relative helicity (SRH, a measure of low-level wind shear that can help with generating tornadoes) was larger over Alabama (middle panel). Some low-level mixed-layer instability (0-3 km mlCAPE, 3rd panel) was also co-located with the increased SRH over central AL, suggesting potential for low-level storm updraft stretching with the supercell moving into the Birmingham area:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhn8DFP5ZRek1MxPLuY0CBhMcnvC0NvOKgZw_1u7dbruD7VWCrvfiF3Ju8KZK5AkPJpNtbVcCjQZjfoHyMa7TpWeMet0nTdWL1CsTXy5eZoMiAzQRK0x-Xg94v6jS3lfAialowPEwVMxL8l/s928/012621spc_mlcpe-srh1-cp304_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="435" data-original-width="928" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhn8DFP5ZRek1MxPLuY0CBhMcnvC0NvOKgZw_1u7dbruD7VWCrvfiF3Ju8KZK5AkPJpNtbVcCjQZjfoHyMa7TpWeMet0nTdWL1CsTXy5eZoMiAzQRK0x-Xg94v6jS3lfAialowPEwVMxL8l/w640-h300/012621spc_mlcpe-srh1-cp304_anno.jpg" width="640" /></a></div><br /><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>Finally, here is a 1-hr HRRR model forecast sounding for 0400 UTC (10:00 pm CST) at Birmingham, roughly 40 minutes before the tornado (important parameters are highlighted in yellow):</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKQMfViSckTtHy3nP0i8blPgwkAa7QKu53tOALnzjU0Hufeskh_qdTKnYvT-WzUIqbHT61KHwxEGr5o0_k00uBwyzLEA4f5XMnOdiJddANElHdOeibA4OeyAeaDRuCfkziQn5-k8zb-Bda/s1060/012621bhm04hrrf01_pvt_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="714" data-original-width="1060" height="432" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKQMfViSckTtHy3nP0i8blPgwkAa7QKu53tOALnzjU0Hufeskh_qdTKnYvT-WzUIqbHT61KHwxEGr5o0_k00uBwyzLEA4f5XMnOdiJddANElHdOeibA4OeyAeaDRuCfkziQn5-k8zb-Bda/w640-h432/012621bhm04hrrf01_pvt_anno.jpg" width="640" /></a></div><br /><br /><p></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>The total mlCAPE was only 900 J/kg, but 0-1 km SRH was 350 m2/s2 (quite significant), and some low-level CAPE was also present (40-50 J/kg, not large but adequate). Deep-layer shear (surface to 6 km above ground) was also quite large (> 65 kt). As is typical in cool season cases with not a lot of CAPE but large wind shear, this environment was supportive of tornadoes, particularly with the aforementioned boundary, the broad warm sector through which the supercell was able to travel and organize during the evening, and the increased SRH over AL.</p><p>The Storm Prediction Center (SPC) did a great job issuing a tornado watch shortly before 6:00 pm CST that included western, central and northern AL. Local NWS and TV coverage in the Birmingham area was also on top of the situation during the 10:00-11:00 pm hour, which probably saved lives.</p><p>Let's hope, on top of everything else going on in our country right now, that 2021 is not a year with many tornadoes hitting populated areas. Over the past year, we've been through a lot (ongoing Covid-19, a national election, attempts to deny and overthrow documented election results, a violent assault on our Capitol). And specific to weather, going back to 2019, there was "<a href="https://www.vox.com/policy-and-politics/2019/9/6/20851971/trump-hurricane-dorian-alabama-sharpie-cnn-media" target="_blank">SharpieGate</a>" and the attempt to deny and alter facts about the path of Hurricane Dorian. </p><p>Hopefully, with new leadership emphasizing science and facts, we'll get this deadly coronavirus under control in the coming months, and life ahead will begin to look better again. </p><p>- Jon Davies 1/29/21 </p>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com0tag:blogger.com,1999:blog-2399626414603781513.post-92001603053829818432020-10-31T09:48:00.023-07:002020-10-31T13:24:26.643-07:00Robert (Bob) Johns - dynamic SPC forecaster and researcher - passes away at 78.<p> </p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjrIm08Q6nBWLs1HE7J_92ba_Cr8bV80RaLmZkfjAfbdNANd2SJn8ztbvbueuk5opvnSa0Dl3hKRbBcDBt82nTwXH2tcWg12_jI_26eUIeJECqbsAAjXPu5E9T0rp5vyttxuwEQhChzYoUz/s832/Bob+Johns1+talk+2001+adj.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="616" data-original-width="832" height="296" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjrIm08Q6nBWLs1HE7J_92ba_Cr8bV80RaLmZkfjAfbdNANd2SJn8ztbvbueuk5opvnSa0Dl3hKRbBcDBt82nTwXH2tcWg12_jI_26eUIeJECqbsAAjXPu5E9T0rp5vyttxuwEQhChzYoUz/w400-h296/Bob+Johns1+talk+2001+adj.jpg" width="400" /></a><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjKJOcw7EQvnyF5PkYbpiwLLU4zwTFtHULYC_zkkL_hNoeEoKgQlHnzhcFryjkVctzdhQI2_nWumIQu-12Z2sbMfgMsYcbDzzUEE7T-76kxLGXzxSQVVtIqFGCJW2-lR7b78dgshsLbxWaz/s404/Bob+Johns+SPC+2+anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="404" data-original-width="306" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjKJOcw7EQvnyF5PkYbpiwLLU4zwTFtHULYC_zkkL_hNoeEoKgQlHnzhcFryjkVctzdhQI2_nWumIQu-12Z2sbMfgMsYcbDzzUEE7T-76kxLGXzxSQVVtIqFGCJW2-lR7b78dgshsLbxWaz/s320/Bob+Johns+SPC+2+anno.jpg" /></a></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjRdYFnV_zAHfhWCHVeO27gDOzDrKHb2OumGdzoDlha4hbewXded20plb9eoPZwzQ9KAUAChltYkMwhc_MMtPeLU6dQoVBGHoHDReCQEfOgwmGMNvpLCkRrAY67Zuxa6cOBiLB2Xjr9z_gP/s474/Bob+Johns.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="412" data-original-width="474" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjRdYFnV_zAHfhWCHVeO27gDOzDrKHb2OumGdzoDlha4hbewXded20plb9eoPZwzQ9KAUAChltYkMwhc_MMtPeLU6dQoVBGHoHDReCQEfOgwmGMNvpLCkRrAY67Zuxa6cOBiLB2Xjr9z_gP/s320/Bob+Johns.jpg" width="320" /></a></div></div><p></p><p>This blog post is about Bob Johns, long-time Storm Prediction Center severe weather forecaster/researcher, who passed away at age 78 this past week after a long illness.</p><p>He was such an incredible influence in my life. </p><p>In the late 1980's, I had worked in television and consulting firms for several years without finding much stability or direction in my weather career. I had moved back to my home area to help take care of my ailing mom and assist my dad with his expanding home medical business in rural Kansas. I thought my career in weather was over. </p><p>However, I still had an interest in severe weather.</p><p>In 1989, I drove to Kansas City and the National Severe Storms Forecast Center (NSSFC, now the Storm Prediction Center) to find meteorological maps for some 1988 tornado events (there was no internet with online weather information yet). As I was shuffling through paper in their map archive room, Bob Johns walked by and introduced himself. We started talking, and that conversation changed the course of my life.</p><p>Bob sensed the untapped passion I had for tornado forecasting and severe weather research, something that hadn't been encouraged by anyone I had worked with so far. To my surprise, he enlisted me in a research project he wanted to do using weather balloon soundings archived from the 1980's to examine environments of significant tornadoes using newer measures of wind shear. Something like that wasn't easy to do back then without the sophisticated computer software for analyzing soundings that we have now. </p><p>The result was several research papers we authored together in the early 1990's that laid some groundwork for using wind shear and instability combinations in tornado forecasting. This included the Energy-Helicity Index (along with SPC forecaster and programming wiz John Hart) as a composite parameter in tornado forecasting. </p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjt881N1cnTtVPS6Ii04ua13-63yOC-H8jaBNet9hwvvgRy6KheYeQpxMCpdRJ3pkcgKa3cC6ZxchRz-3nkVQOn9CwqyBe1UWJH4LPZnGe1cP8nQiDak7Qp4XCnOqktAp8mta7yTf0O1lCf/s742/Johns-Davies+paper2+-+Tornado+vol.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="546" data-original-width="742" height="294" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjt881N1cnTtVPS6Ii04ua13-63yOC-H8jaBNet9hwvvgRy6KheYeQpxMCpdRJ3pkcgKa3cC6ZxchRz-3nkVQOn9CwqyBe1UWJH4LPZnGe1cP8nQiDak7Qp4XCnOqktAp8mta7yTf0O1lCf/w400-h294/Johns-Davies+paper2+-+Tornado+vol.jpg" width="400" /></a><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgW_25hWuWyMQLOjjBsUPUrS-TopDigMzriYuQOIm1jAJLPMHZk-ISkOqd9h71ZDfEPLLljn4LA4VzufRUnULUfvjapNKq5ETOqnHVusYIXpF1JoQRO7UiiTDdzdfNvfgvjJgnFUvUNDFUY/s654/Johns-Davies+paper2+-+EHI.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="601" data-original-width="654" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgW_25hWuWyMQLOjjBsUPUrS-TopDigMzriYuQOIm1jAJLPMHZk-ISkOqd9h71ZDfEPLLljn4LA4VzufRUnULUfvjapNKq5ETOqnHVusYIXpF1JoQRO7UiiTDdzdfNvfgvjJgnFUvUNDFUY/s320/Johns-Davies+paper2+-+EHI.jpg" width="320" /></a></div></div><p>I was thrilled that he asked me to work with him on this project. In his quiet but enthusiastic way, one of Bob's gifts was recognizing people's abilities and inspiring them to use and develop them. I am very blessed that he took an interest in me, and his mentorship was essential in nudging me in a different direction at a key time in my life.</p><p>Here'a photo of NSSFC staff back in 1977: along with Bob Johns, it includes forecasters Steve Weiss, Larry Wilson, and Jack Hales. Bob introduced me to these NSSFC 'stalwarts', who were all very kind and encouraging to me. I also met severe weather icons Chuck Doswell, Don Burgess, Robert Davies-Jones, and others through him, which was quite amazing yet humbling for someone so new to weather research and writing. </p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh7_YnU8gibWsbrEWjOaGDNti6OVridtQZ2usvbIgiT4nt1ZJvGqSLMh5t7qBCHlXWwHquEk7oyvK1nDGvnsQCqUbH3kPvr-7PdEjIkl-d05m4TMG1uQ3mI6Z0PWYCTp5IcGIV6v1uDGfbO/s561/Bob+Johns+SPC+1+anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="318" data-original-width="561" height="226" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh7_YnU8gibWsbrEWjOaGDNti6OVridtQZ2usvbIgiT4nt1ZJvGqSLMh5t7qBCHlXWwHquEk7oyvK1nDGvnsQCqUbH3kPvr-7PdEjIkl-d05m4TMG1uQ3mI6Z0PWYCTp5IcGIV6v1uDGfbO/w400-h226/Bob+Johns+SPC+1+anno.jpg" width="400" /></a></div><p>Bob started at NSSFC in Kansas City in 1971, learned much about severe weather forecasting and issuing watches from forecaster Larry Wilson, and became a lead forecaster at NSSFC by 1979. He worked in that capacity until 1994 when he became Scientific Operations Officer at the time SPC moved to Norman, Oklahoma. He retired in 2001, after which he worked part-time. It is noteworthy that Bob introduced the enhanced "Particularly Dangerous Situation" (PDS) wording to tornado watches during the 2 April 1982 tornado outbreak in Texas, Arkansas, and Oklahoma.</p><p>Chicago weather legend Tom Skilling wrote the following on Facebook after Bob John's passing this week:</p><p></p><blockquote><p>"<i>Anyone who has worked in the meteorological profession has read and studied Johns' remarkable work on severe weather--work produced over an amazing decades-long career...</i></p><p><i>I first met Bob at one of our Fermilab Tornado and Severe Weather seminars back in the 1990s... For someone who had so profoundly impacted the meteorological profession over his decades long career, it was such a joy to discover a soft-spoken man with a warm smile. Bob was so kind and so easy to approach... He had a passion toward meteorology and, in particular, severe weather and the manner in which nature put it together. He spent his professional life cataloging what he had learned and worked tirelessly passing this information on to his colleagues and all interested in the subject.</i>"</p></blockquote><p></p><p>I couldn't describe Bob better myself. As Tom also mentioned in his FB post:</p><p></p><blockquote>"<i>His work on the prediction of "derechoes", the fast moving and destructive squall lines like the one which raced across our area at highway speed this past August, has been described as the "bible" on the subject for forecasters. His forecast techniques are still in use today. Johns published his study on the phenomenon with his National Weather Service colleague Bill Hirt in 1987.</i>"</blockquote><p></p><p>Here's that paper: <a href="https://journals.ametsoc.org/waf/article/2/1/32/38564/Derechos-Widespread-Convectively-Induced" target="_blank"> Johns, R. H., and W. D. Hirt, 1987: Derechos: widespread convectively induced windstorms. Wea. Forecasting, 2, 32-49</a>.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgk_0tpU9ajbdmZp_s6HBvHty2NwZi0d-Eut_Oa3Lf89rOnQbrRcXLUZ08JQNls-1pJR_PJs5UBEHBHKz_6b75Y9oV71SNXdopv0X0ByKtx5axhbG4c_DoYcvwoVyLm4aKFwc4Rspe4APh8/s720/Bob+Johns+-+Derecho+1987+paper.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="584" data-original-width="720" height="325" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgk_0tpU9ajbdmZp_s6HBvHty2NwZi0d-Eut_Oa3Lf89rOnQbrRcXLUZ08JQNls-1pJR_PJs5UBEHBHKz_6b75Y9oV71SNXdopv0X0ByKtx5axhbG4c_DoYcvwoVyLm4aKFwc4Rspe4APh8/w400-h325/Bob+Johns+-+Derecho+1987+paper.jpg" width="400" /></a></div><p>Bob's work on derechos (see <a href="http://davieswx.blogspot.com/2020/08/the-august-10-2020-midwest-derecho-how.html" target="_blank">my blog post on last August's derecho</a>) helped make meteorologists and the public more aware of these large, destructive, and potentially deadly windstorms that can blast across several states. His research has saved lives as a result.</p><p>Here's references for a little more of Bob's work:</p><p></p><ul style="text-align: left;"><li><a href="https://journals.ametsoc.org/waf/article/7/4/588/40419/Severe-Local-Storms-Forecasting" target="_blank"><i>Johns, R. H, and C. A. Doswell III, 1992: Severe local storms forecasting. Wea. Forecasting, 7, 588-612.</i></a></li><li><a href="https://journals.ametsoc.org/waf/article/8/2/294/40396/Meteorological-Conditions-Associated-with-Bow-Echo" target="_blank"><i>Johns, R. H., 1993: Meteorological conditions associated with bow echo development in convective storms. Wea. Forecasting, 8, 294-299.</i></a></li><li><i>Johns, R. H., J. M. Davies, and P. W. Leftwich, 1993: Some wind and instability parameters associated with strong and violent tornadoes, 2. Variations in the combinations of wind and instability parameters. The Tornado: Its Structure, Dynamics, Prediction, and Hazards, Geophys. Monogr., No. 79, C. Church, D. Burgess, C. Doswell III, and R. Davies-Jones, Eds., Amer. Geophys. Union, Washington, DC, 583-590.</i></li><li><a href="http://nwafiles.nwas.org/digest/papers/1996/Vol20No4/Pg2-Johns.pdf" target="_blank"><i>Johns, R. H., and R. A. Dorr, Jr., 1996: Some meteorological aspects of strong and violent tornado episodes in New England and eastern New York. Natl. Wea. Dig., 20:4, 2-12</i></a></li><li><i><a href="https://ejssm.org/ojs/index.php/ejssm/article/view/109/89" target="_blank">Johns, R. H., D. W.Burgess, C. A.Doswell III, M. S.Gilmore, J. A.Hart, and S. F.Piltz, 2013: The 1925 Tri-State tornado damage path and associated storm system. Electronic J. Severe Storms Meteor., 8, http://ejssm.org/ojs/index.php/ejssm/article/viewArticle/109.</a></i></li></ul><p></p><p>As the last paper above reflects, Bob spent years studying and reconstructing the damage path of the famous 1925 Tri-State tornado in Missouri, Illnois, and Indiana. It was a serious and fascinating subject for him. That classic 2013 paper Bob wrote with Chuck Doswell, Don Burgess, and John Hart serves as the authoritative documentation and reference for that remarkable tornado.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgPnLFT8AhJPrTRiYcSMWQalkfhgjqTnHJqefQWJBHk0kGBu78wn4NWeafPlT9fhUcnrTIzRQ60uK9Tk_md5uE2qWzHosf6gc-VZvZVsGaO3bT6jd0kn3AvI677KAfuwdLOSr9-4fYMop0H/s537/Bob+Johns+-+tri-state+tor+1925+path.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="326" data-original-width="537" height="243" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgPnLFT8AhJPrTRiYcSMWQalkfhgjqTnHJqefQWJBHk0kGBu78wn4NWeafPlT9fhUcnrTIzRQ60uK9Tk_md5uE2qWzHosf6gc-VZvZVsGaO3bT6jd0kn3AvI677KAfuwdLOSr9-4fYMop0H/w400-h243/Bob+Johns+-+tri-state+tor+1925+path.jpg" width="400" /></a></div><div><br /></div>Bob even wrote a book on the Tri-State Tornado, which you can <a href="https://www.amazon.com/Tri-State.../dp/1468560964/ref=nodl_" target="_blank">buy on Amazon</a>.<div><br /><p>A more comprehensive list of Bob's published papers can be downloaded here: <a href="http://www.ejssm.org/ojs/index.php/ejssm/article/downloadSuppFile/29/79" target="_blank">http://www.ejssm.org/ojs/index.php/ejssm/article/downloadSuppFile/29/79</a></p><p>And for those who'd like more background on Bob John's growing up in Indiana and the development of his passion for severe weather, here's John M. Lewis' article about him in 2007: <a href="https://ejssm.org/ojs/index.php/ejssm/article/view/29/32">https://ejssm.org/ojs/index.php/ejssm/article/view/29/32</a></p><p>Back in 2001, I was honored to be part of an evening seminar and review of the 1991 Andover, Kansas tornado where Bob talked about his handling of the event as a forecaster at NSSFC/SPC:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjh8czudp0UDbjJQGegR7PTB0_S2Ufl5a0qRtIX1g7kdxz2cBkp8nAzSt0xOl-8LvlnICRvK23V2YiXIKo0PfQE_R-AN1nUm7E2W5Pb-Yq0q-pGvNMwBNxL99hrMLA86UtAPiJQM17mE0Dz/s766/Bob+Johns+%2526+me+Andover+seminar+2001+anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="535" data-original-width="766" height="279" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjh8czudp0UDbjJQGegR7PTB0_S2Ufl5a0qRtIX1g7kdxz2cBkp8nAzSt0xOl-8LvlnICRvK23V2YiXIKo0PfQE_R-AN1nUm7E2W5Pb-Yq0q-pGvNMwBNxL99hrMLA86UtAPiJQM17mE0Dz/w400-h279/Bob+Johns+%2526+me+Andover+seminar+2001+anno.jpg" width="400" /></a></div><p>He taught me so much about research, staying disciplined, being practical, and staying clear in my focus and writing. Bob helped give me confidence that I was missing in my young life, and he also taught me about being a decent human being, I owe him a great deal. </p><p>A final thought... Bob Johns was a wonderful reminder that we should treat those newer people finding their way in our chosen profession with respect and a helpful spirit. He exemplified the importance of 'paying it forward' when we've had the good fortune to do what we love.</p><p>Rest in Peace, my friend. You will not be forgotten.</p><p><br /></p><p>- Jon Davies 11/30/20</p><div><br /></div></div>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com1tag:blogger.com,1999:blog-2399626414603781513.post-26234681952065708212020-09-01T09:09:00.004-07:002020-09-01T15:19:05.995-07:00Landspouts and the meteorological ingredients that can produce them<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhHPfRoHJZHBe8rv9lMY8fkxQ6dCJMveL7CwaBzinTLQqxhzhiBky3R4r8bH3bDDJhzOMBcD6uO1xITKAV3B4vbufxTqo4xa9EXcaBnhwtG9Iv1-P4-zYDQmTwdydJ9h-U2T6E0aH4B0D0v/s598/062120nwKSlndspt_mt4_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="598" data-original-width="406" height="478" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhHPfRoHJZHBe8rv9lMY8fkxQ6dCJMveL7CwaBzinTLQqxhzhiBky3R4r8bH3bDDJhzOMBcD6uO1xITKAV3B4vbufxTqo4xa9EXcaBnhwtG9Iv1-P4-zYDQmTwdydJ9h-U2T6E0aH4B0D0v/w325-h478/062120nwKSlndspt_mt4_anno.jpg" width="325" /></a></div><p>I've had some requests to update some material about landspout tornadoes that used to be on an old web site of mine, which is the reason for this post. </p><p>A landspout tornado is a type of non-supercell tornado that can occur with a thunderstorm that doesn't have a rotating updraft detectible on radar (a mesocyclone). Because of this, warnings can't be issued for landspout tornadoes based on radar - they have to be reported by spotters and storm chasers, and there is no warning lead time. Thankfully, most landspout tornadoes are relatively weak, but on occasion they can become strong in the right setting.</p><p>How do landspout tornadoes form?</p><p>First, a sharp wind shift boundary must be present. That's what provides the vorticity (or 'spin') needed for the tornado, when the low-level wind shear that helps to generate supercell tornadoes is absent:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgFxhqLr5c_MzuyhaS_SpjlK99127uACQZ1BVLIy0u_5lZIeR-juCj2GjV2j30_7eB38fR_ItZNCBG2KxXzs5bm0ZzHU9w5II6YUHVG53e8XdREQ3wSY0dLwpBZI849B_-7k4b5WWaq-336/s369/landspout_process-W%2526W89_a.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="312" data-original-width="369" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgFxhqLr5c_MzuyhaS_SpjlK99127uACQZ1BVLIy0u_5lZIeR-juCj2GjV2j30_7eB38fR_ItZNCBG2KxXzs5bm0ZzHU9w5II6YUHVG53e8XdREQ3wSY0dLwpBZI849B_-7k4b5WWaq-336/s0/landspout_process-W%2526W89_a.jpg" /></a></div><p>Second, instability (or CAPE - convective available potential energy) must be present along the boundary for a thunderstorm updraft to develop. In particular, CAPE in the lowest 3 km above ground helps because it can facilitate low-level stretching in updrafts along the boundary due to the instability being located closer to the ground. </p><p>Third, steep low-level lapse rates (a rapid drop off in temperature in the lowest few kilometers above ground due to strong daytime surface heating) can also help accelerate low-level air upward in updrafts, increasing low-level stretching.</p><p>Here's one example of these ingredients coming together in a setting that might generate and support landspout tornadoes, using <a href="https://www.spc.noaa.gov/exper/mesoanalysis/" target="_blank">SPC mesoanalysis page</a> graphics: </p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjzhDshjOONHBpvhNbGN0YsgQkbmbvrxBAEyhjhdwe3DwdkBeYHqH9EiIT_KGvxY7A6GosQ5eNaa-ArdgfyD0BNw37KHjs7FJyimkzCNcJMyxzQ0SCeeoUtjnZtoKgudBoYaX_rZIwezHDJ/s830/landspout_cp3-lr3-mlcpe.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="281" data-original-width="830" height="217" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjzhDshjOONHBpvhNbGN0YsgQkbmbvrxBAEyhjhdwe3DwdkBeYHqH9EiIT_KGvxY7A6GosQ5eNaa-ArdgfyD0BNw37KHjs7FJyimkzCNcJMyxzQ0SCeeoUtjnZtoKgudBoYaX_rZIwezHDJ/w640-h217/landspout_cp3-lr3-mlcpe.jpg" width="640" /></a></div><p></p><p>If a thunderstorm updraft forms on a sharp boundary in such an environment with everything coming together just right (for example, the storm updraft must develop directly over the boundary and align properly with a small 'wiggle' or pocket of 'spin' on the boundary), the thunderstorm may then generate a landspout tornado through upward stretching of that 'spin':</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiFB9VrcLcjkDG2GWJewz6TnVFxchptHC5TyXrGMfJBqqIahWhVozbueNtMMFSbSCF9jEOkbB0Bb9SHVrZo4zeATDm_S8QjKGjByg4ZGSS7cPXpDw08HP1Hd88tfRyzg_RbTdNnsEpyyiWN/s358/landspout_process-W%2526W89_b.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="312" data-original-width="358" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiFB9VrcLcjkDG2GWJewz6TnVFxchptHC5TyXrGMfJBqqIahWhVozbueNtMMFSbSCF9jEOkbB0Bb9SHVrZo4zeATDm_S8QjKGjByg4ZGSS7cPXpDw08HP1Hd88tfRyzg_RbTdNnsEpyyiWN/s0/landspout_process-W%2526W89_b.jpg" /></a></div><p><br /></p><p>Here's an example of a setting for landspout tornadoes that occurred on May 25, 2018 in both southern Minnesota (MN) and eastern Nebraska (NE). The surface map at early afternoon on 5/25/18 showed a relatively stationary wind shift boundary (thick brown dashed line) stretching from a low in southern MN into east-central NE:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEja_POBzywNUZpT3DNedIrd9qKMrp50a1ViNNJUF4x9Vy8NJKBz-K5IxgAN4XwnBP7mgfQC2Mgi6F-dhyphenhyphen60Yg-S0jl1f-HppiTnXG-XnQ18MUm71ZzX6Fj7MzRmu7NiI3PjhAUOO9ie3KjZ/s527/052518sfc1858_anno2.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="527" data-original-width="483" height="422" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEja_POBzywNUZpT3DNedIrd9qKMrp50a1ViNNJUF4x9Vy8NJKBz-K5IxgAN4XwnBP7mgfQC2Mgi6F-dhyphenhyphen60Yg-S0jl1f-HppiTnXG-XnQ18MUm71ZzX6Fj7MzRmu7NiI3PjhAUOO9ie3KjZ/w386-h422/052518sfc1858_anno2.jpg" width="386" /></a></div><p>SPC mesoanalysis graphics at early afternoon on 5/25/18 showed plentiful low-level instability (0-3 km CAPE, in red, 1st panel below) over southern MN near the surface low where a storm was developing on the boundary (light blue lines also show surface vorticity or 'spin' along this boundary). The 2nd panel below showed low-level lapse rates (0-3 km) to be steep over a large area, including all along the boundary, with lapse rates > 8.0 deg C shaded in orange:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjKZIJxqHmTZPOnAsY5rQoVrW_ZIBYc_EDql6S2JKzAoqTEem8_d1EWTT8SsxCtgtI8tvFtNEf90mKd0qK5GSJfbXH5XA7Cyr-MHE4r7W4a6hvq7tIhAOfvJPWuI7wTirxfGZKbVO4z12lG/s847/052518spccp3-lr3_18-19z.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="424" data-original-width="847" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjKZIJxqHmTZPOnAsY5rQoVrW_ZIBYc_EDql6S2JKzAoqTEem8_d1EWTT8SsxCtgtI8tvFtNEf90mKd0qK5GSJfbXH5XA7Cyr-MHE4r7W4a6hvq7tIhAOfvJPWuI7wTirxfGZKbVO4z12lG/s640/052518spccp3-lr3_18-19z.jpg" width="640" /></a></div><p>Below is the developing storm on visible satellite (yellow arrow) at about 2 pm CDT. Less than an hour later, a landspout tornado developed on the southwest edge of this new storm (photos also below):</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgHZHc0SSms2fGZDY1T4dv1_6m0asxuUOKilgIUkGaaVqP73KwU5RYkMNuR9efCccGOCLOmmvjC1HH7KKtGU84khYGcA5ufTFCyeNJEqrSvVWUyF2K31xX-iI2oHV9zhdX-3GS6wTMvCRcm/s532/052518sa1903_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="508" data-original-width="532" height="406" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgHZHc0SSms2fGZDY1T4dv1_6m0asxuUOKilgIUkGaaVqP73KwU5RYkMNuR9efCccGOCLOmmvjC1HH7KKtGU84khYGcA5ufTFCyeNJEqrSvVWUyF2K31xX-iI2oHV9zhdX-3GS6wTMvCRcm/w426-h406/052518sa1903_anno.jpg" width="426" /></a></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi4p4_XZjL7S194DzwzJR65k1CIAgu7hMraR_tlU4v6uujFZgqqbYEbFkLJt4ln43Ntxg7VY7zJnI0_2e0cowCt8wufsSMm6-XTtImRfaeljid9a0M8oTMEpkrWsZ00vOY-jjc3uHBAMjfG/s470/052518scMNlndspt_bs_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="470" data-original-width="418" height="376" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi4p4_XZjL7S194DzwzJR65k1CIAgu7hMraR_tlU4v6uujFZgqqbYEbFkLJt4ln43Ntxg7VY7zJnI0_2e0cowCt8wufsSMm6-XTtImRfaeljid9a0M8oTMEpkrWsZ00vOY-jjc3uHBAMjfG/w334-h376/052518scMNlndspt_bs_anno.jpg" width="334" /></a><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiikboG0MOKL_tKq8muWTQUVUBtq_3GR-4XXw5sTTIVpqEZjzn6cVKh47Z0tTrrYvoY-evWFU_456OvKgDHJEllwJ1UgIcSEcg8V4tBapFp4VHyLWcCiEnNel3SZcrSM9Xo5gWKfA7MBAxn/s376/052518scMNlndspt_js_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="376" data-original-width="282" height="376" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiikboG0MOKL_tKq8muWTQUVUBtq_3GR-4XXw5sTTIVpqEZjzn6cVKh47Z0tTrrYvoY-evWFU_456OvKgDHJEllwJ1UgIcSEcg8V4tBapFp4VHyLWcCiEnNel3SZcrSM9Xo5gWKfA7MBAxn/w283-h376/052518scMNlndspt_js_anno.jpg" width="283" /></a></div></div><p>From the 5/25/18 surface and SPC graphics up above, notice that all of the ingredients listed earlier for supporting landspout tornadoes (boundary, instability, steep low-level lapse rates) were present in this case, increasing the possibility of a landspout tornado _if_ the storm aligned properly with the boundary and the 'spin' along it.</p><p>Later in the afternoon, other storms developed southwestward on the wind shift boundary over Iowa and Nebraska. After 5 pm CDT, a small high-based storm on the boundary over northeast/east-central NE (yellow arrow in satellite photo below) apparently "phased' with the boundary enough to produce yet another landspout tornado (see photos below):</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgK63_Qy7IYEqFVz1n1NlO3VahMV4XzIB7NLIh0kBVfr1JmIlxvx-XdfKPOzYlHnp0l2B8DPUMurmdLpjVXl48Pi2Y6RCVuvqHjpN6w9cbOS1CN-o1RnF1sXKnt6RyyMkay08RcnIrUca1k/s531/052518sa2218_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="511" data-original-width="531" height="409" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgK63_Qy7IYEqFVz1n1NlO3VahMV4XzIB7NLIh0kBVfr1JmIlxvx-XdfKPOzYlHnp0l2B8DPUMurmdLpjVXl48Pi2Y6RCVuvqHjpN6w9cbOS1CN-o1RnF1sXKnt6RyyMkay08RcnIrUca1k/w425-h409/052518sa2218_anno.jpg" width="425" /></a></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjz2Bl2-4fiD8_-fkX3h8iPeSk8XkAI5zdjUApGvNVgtY44EsOx0qvg5u0SLFxcS-k21f9C6v9utz28TvZDYmR18gskCrBxwnblalQa3ZW3zlB6DxdJQAV1Amhde8gbrCuioukP9Ghi9ecb/s462/052518cNElndspt_dc_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="278" data-original-width="462" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjz2Bl2-4fiD8_-fkX3h8iPeSk8XkAI5zdjUApGvNVgtY44EsOx0qvg5u0SLFxcS-k21f9C6v9utz28TvZDYmR18gskCrBxwnblalQa3ZW3zlB6DxdJQAV1Amhde8gbrCuioukP9Ghi9ecb/s0/052518cNElndspt_dc_anno.jpg" /></a></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgKxzd2qZ9TBpiHEDZcBjPRpBBIW803DBGh3CuHhx9L6yWt9NML8XSyLVVHnAQgavmaH9DfN5HkITBFWXVXT7D1a150K89hyiOtn6ZIk4ocymXCeR5GAp83QQnEA_2a3aK_ADCex_ofD-v6/s602/052518cNElndspt_kk2_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="435" data-original-width="602" height="348" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgKxzd2qZ9TBpiHEDZcBjPRpBBIW803DBGh3CuHhx9L6yWt9NML8XSyLVVHnAQgavmaH9DfN5HkITBFWXVXT7D1a150K89hyiOtn6ZIk4ocymXCeR5GAp83QQnEA_2a3aK_ADCex_ofD-v6/w482-h348/052518cNElndspt_kk2_anno.jpg" width="482" /></a></div><p>As can be seen from the satellite photo, there were _many_ storms that developed along the boundary by late afternoon, but only _one_ of the Nebraska storms produced a tornado. This certainly highlights that landspout tornadoes are not really forecast-able in advance. A meteorologist can only note that ingredients possibly supportive of landspout tornadoes (the boundary, instability, low-level lapse rates) appear to be coming together in an area, so that reports of such tornadoes are not a surprise and can be warned immediately when spotted. </p><p>Here are a few landspout tornado cases I've posted about on my blog:</p><p> <a href="http://davieswx.blogspot.com/2020/06/a-look-landspout-tornado-formation-in.html" target="_blank">June 21, 2020 landspout tornado in northwest Kansas</a><br /></p><p> <a href="http://davieswx.blogspot.com/2019/04/landspout-type-setting-produces-first.html" target="_blank">April 17, 2019 landspout tornadoes in Oklahoma, Kansas, and Texas</a><br /></p><p> <a href="http://davieswx.blogspot.com/2012/05/prolific-non-supercell-tornado-outbreak.html" target="_blank">May 19, 2012 non-supercell tornado outbreak in southern Kansas</a><br /></p><p>And, for more technical reference, here are some papers that discuss landspout tornadoes:</p><p> <a href="https://journals.ametsoc.org/mwr/article/117/6/1113/64143/Non-supercell-Tornadoes" target="_blank"> Non-supercell tornadoes (Wakimoto and Wilson 1989)</a><br /></p><p> <a href="https://pdfs.semanticscholar.org/b878/c75ba13ea93ee9cecab25e245d82563e6abb.pdf" target="_blank">Tornadoes in non-mesocyclone environments with pre-existing vertical vorticity along convergence boundaries (Caruso and Davies 2005)</a><br /></p><p> <a href="https://journals.ametsoc.org/waf/article/21/4/579/38865" target="_blank">Tornadoes in environments with small helicity and/or high LCL heights (Davies 2006) </a></p><p>It is also important to recognize that there are some cases where both non-supercell and supercell processes appear to be at work, particularly when winds aloft are strong enough to support and organize storms into supercells while ingredients related to landspout tornadoes are also present. This is particularly true in the High Plains of the U.S., and such "hybrid" events are difficult to categorize. Here are a couple examples:</p><p> <a href="http://davieswx.blogspot.com/2019/07/a-surprise-photogenic-tornado-in.html" target="_blank"> June 29, 2019 long-lived tornado in southwest South Dakota</a><br /></p><p> <a href="http://davieswx.blogspot.com/2018/06/the-awesomely-photogenic-laramie-wy.html" target="_blank">June 6, 2018 large and long-lived tornado near Laramie, Wyoming</a><br /></p><p>Hopefully, this short discussion will help those interested in understanding some of the important factors and ingredients that contribute to landspout tornadoes.</p><p>- Jon Davies 9/1/20</p><p><br /></p>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com0tag:blogger.com,1999:blog-2399626414603781513.post-17409703888902172602020-08-13T16:04:00.020-07:002020-08-14T13:08:15.987-07:00The August 10, 2020 Midwest Derecho - how did it develop?<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi3e9Et2_05YId49gt_kmhzc6JqQofRwWX_1Y1UVowOCZjy5z5eszzZCAJ2bU9_NB8VuLGwAR-tMP4-OPp7az9H4-fpJqUX6nGXjwEcvrNCY439sPF5fJcpfkjm-tYAkUeS_90lvj3XsYTG/s1043/081020neILderecho_nu2_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="600" data-original-width="1043" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi3e9Et2_05YId49gt_kmhzc6JqQofRwWX_1Y1UVowOCZjy5z5eszzZCAJ2bU9_NB8VuLGwAR-tMP4-OPp7az9H4-fpJqUX6nGXjwEcvrNCY439sPF5fJcpfkjm-tYAkUeS_90lvj3XsYTG/s640/081020neILderecho_nu2_anno.jpg" width="640" /></a></div><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEidHfzf9OUANKM8LSegDUwfVKIGGXmYH-T34wAGMsYFLCbVNqH84SRuYDZ7r_qADb5xg9f5o5GOrYwC7dGxRU1euayZm1QS-aq4VUnFVM9fn58HawiQ2DIKSFgkg8GbqVujccd4ZRPNTyh6/s1220/081020nwIAderecho_as2_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="487" data-original-width="1220" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEidHfzf9OUANKM8LSegDUwfVKIGGXmYH-T34wAGMsYFLCbVNqH84SRuYDZ7r_qADb5xg9f5o5GOrYwC7dGxRU1euayZm1QS-aq4VUnFVM9fn58HawiQ2DIKSFgkg8GbqVujccd4ZRPNTyh6/s640/081020nwIAderecho_as2_anno.jpg" width="640" /></a></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjlWPh08nB-5xsKG0CMQppGvWtrav6JpPEJjOHomB76tIMwdUSEKljnWz_H4KDli20wd3mE_x4oTb9zt5FShOsujRUEcE1gbJJbuyHYJDmm91e3n_KN4zwFaNoDhEgMp4_e_ZIX2VXQiK5m/s686/081020cIAderecho_rb_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="373" data-original-width="686" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjlWPh08nB-5xsKG0CMQppGvWtrav6JpPEJjOHomB76tIMwdUSEKljnWz_H4KDli20wd3mE_x4oTb9zt5FShOsujRUEcE1gbJJbuyHYJDmm91e3n_KN4zwFaNoDhEgMp4_e_ZIX2VXQiK5m/s640/081020cIAderecho_rb_anno.jpg" width="640" /></a></div>Winds from the derecho on Monday, August 10 (pronounced 'day-ray-cho', a widespread convective system with high winds over a large area that can affect several states) killed two people, one in Iowa and one in Indiana, while leaving over a million people without electricity. The images above show the derecho moving into Chicago at mid-afternoon, the derecho's shelf cloud approaching Sioux City, Iowa on Monday morning, and major damage in Marshalltown, Iowa at mid to late morning. <p></p><p>The derecho capped off a very active (for August) 7-day period of severe weather. August 3-4 saw numerous tornadoes associated with the remnants of Hurricane Isaias from North Carolina (where 2 people died in a nighttime EF3 tornado) to Virginia, Maryland, Delaware, Pennsylvania, and New Jersey. Then an EF2 tornado on the evening of August 7 killed two people in southwest Manitoba, Canada.</p><p>Monday's derecho started in the early morning hours over South Dakota, crossed Iowa during the morning, and hit Chicago and northern Indiana in the afternoon. Here's an hour by hour composite radar image from NWS Chicago that shows the derecho's rapid progress:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiss5ElLpGdnkkQCi00D6_ZNySNpzSY_wbWd_7VDLUzEVPW0zz_6P4-Mvy7-p6KwFl3He_z42cl-Y_ToFVedlZr8Jc73tKMCvsgvTfwgSZyKpELUWoNRy4Dq6Z9hMUKVOGsbpZwP4HXrLXa/s1008/081020rdr_derecho_13z-23z.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="579" data-original-width="1008" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiss5ElLpGdnkkQCi00D6_ZNySNpzSY_wbWd_7VDLUzEVPW0zz_6P4-Mvy7-p6KwFl3He_z42cl-Y_ToFVedlZr8Jc73tKMCvsgvTfwgSZyKpELUWoNRy4Dq6Z9hMUKVOGsbpZwP4HXrLXa/s640/081020rdr_derecho_13z-23z.jpg" width="640" /></a></div><p><br /></p><p>And here's the associated storm reports showing the wide axis of damage across several states, including some embedded "bow echo" or QLCS-type EF0-EF1 tornadoes in the Chicago area:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiU-VTxS2rPUODrS5wb6SVu8eg38bCyyZ3uqhwPAQWRvznTSdFCLC-huDUJztCgVvB677EeHasCdrgRJcsw9p25o9QfkxXFXCciMNYKPeh3wiX6fE-mGpKf7RND7lgnESLozmP6ShO_y-zN/s641/081020derecho_stmrpts.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="375" data-original-width="641" height="299" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiU-VTxS2rPUODrS5wb6SVu8eg38bCyyZ3uqhwPAQWRvznTSdFCLC-huDUJztCgVvB677EeHasCdrgRJcsw9p25o9QfkxXFXCciMNYKPeh3wiX6fE-mGpKf7RND7lgnESLozmP6ShO_y-zN/w512-h299/081020derecho_stmrpts.jpg" width="512" /></a></div><div class="separator" style="clear: both; text-align: center;"><br /></div><p>How does a derecho like this form? Large convective systems are pretty common across the Midwest in summertime. So, what causes one of these systems to become a dangerous and deadly squall line or cluster of storms? Answers have to do with the origin area of the derecho (south-central/southeast South Dakota in this case), as well as the synoptic setting out ahead of it.</p><p>Below is the surface map at 5:00 am CDT on 8/10/20, along with a radar inset focused on south-central South Dakota (SD). I've indicated the genesis region of the derecho, where an area of thunderstorms had formed during the early a.m. hours within the thick black oval on the surface map, north of a frontal boundary over Nebraska:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhGinPzjL2h_Li1LlfUHc7Yp74JHTOMVS0v4hhv5pP4KyAD0rRr7bWszAmGNvBFWxwU-A97DguZ9GMxO2I1PC2AkB07tq3_Be4c1WUgpTFYsQ4Emxs-hmF2sSY4yu3IkKzIsGu1Htbvywsb/s774/081020sfc-rd0958_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="616" data-original-width="774" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhGinPzjL2h_Li1LlfUHc7Yp74JHTOMVS0v4hhv5pP4KyAD0rRr7bWszAmGNvBFWxwU-A97DguZ9GMxO2I1PC2AkB07tq3_Be4c1WUgpTFYsQ4Emxs-hmF2sSY4yu3IkKzIsGu1Htbvywsb/s640/081020sfc-rd0958_anno.jpg" width="640" /></a></div><p></p><p>A RAP model forecast sounding at Lake Andes, SD, just east of these thunderstorms, is shown below:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjA5yEbFsVw-LSQ3W9TLUIbDyf0y5iK0HTmSPgz4ZIiYvSNRszFalxiKK3jvhT6TiLb9W9P6ZP58QQSCDSeZbQ2d9ZoNY3AmXnn32Z7wQW8AHZ8mXQWHKpge1olqP6Rm3FeHW1-bKDREVKN/s713/081020lakeandesSD10rapf01_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="501" data-original-width="713" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjA5yEbFsVw-LSQ3W9TLUIbDyf0y5iK0HTmSPgz4ZIiYvSNRszFalxiKK3jvhT6TiLb9W9P6ZP58QQSCDSeZbQ2d9ZoNY3AmXnn32Z7wQW8AHZ8mXQWHKpge1olqP6Rm3FeHW1-bKDREVKN/s640/081020lakeandesSD10rapf01_anno.jpg" width="640" /></a></div><p></p><p>Notice that there was a significant layer of dry air in the lowest 3 km, indicated by the broad distance between the red temperature and blue dew point curves in lower levels. This was _below_ a relatively moist layer beginning at roughly 3 km above ground where significant CAPE was present from a lifted parcel at that elevated level. With little or no convective inhibition (CIN) at this level, elevated storms could initiate well north of the surface front over Nebraska (see 5:00 am surface map earlier), and rain into this dry layer below.</p><p>This would produce strong evaporative cooling, creating dense cool air accelerating downward and outward and generating strong surface winds beneath and ahead of the expanding elevated storms over southern SD. Here's a diagram illustrating that process for many summertime derechos that initiate in the northern Plains of the U.S.:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgusIJftQuWTcqv_oRZcv3pQLmwww1vgxsDdBGHB2VsIdP50EraUI9uGMSnKwv-mxClOpnhITcZtXPReN4yBHoNPbpmlsjK7Tjvsg8n2r_DPoYic1I5P4hPJ6QQ2QFsw_2-f-AfrJxg9Tc9/s669/derecho_evap_cooling_diagram.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="414" data-original-width="669" height="317" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgusIJftQuWTcqv_oRZcv3pQLmwww1vgxsDdBGHB2VsIdP50EraUI9uGMSnKwv-mxClOpnhITcZtXPReN4yBHoNPbpmlsjK7Tjvsg8n2r_DPoYic1I5P4hPJ6QQ2QFsw_2-f-AfrJxg9Tc9/w512-h317/derecho_evap_cooling_diagram.jpg" width="512" /></a></div><p>This may look similar to diagrams of downbursts and microbursts, which are much more localized. But what is different and important in Monday's case is that the evaporative cooling and downward air acceleration was taking place over a larger area with the _cluster_ of developing storms, rather than a single thunderstorm. This then spread out into the broad squall line and convective system seen in the composite progressive radar image earlier.</p><p>I should emphasize that soundings like the one at Lake Andes up above, with a moist layer of sizable elevated CAPE above a significant layer of dry air (a type of 'overrunning' situation, north of the Nebraska frontal boundary seen on the earlier surface map) are not that common. With a developing thunderstorm cluster, it's a little unusual to see such an elevated moist layer located that far above a depth of much drier air beneath.</p><p>Below is the 500 mb NAM model forecast for 4:00 am CDT in the mid-levels of the atmosphere on 8/10/20, showing a significant shortwave disturbance (thick dashed black line) moving across the northern Plains. This disturbance provided the upward forcing that helped fire up the elevated thunderstorms over southern SD that evolved into the derecho:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgNXcO_eY8Z5Aq3LZKC4tyrPcVFKOQYsNpGmLy42Nui74FrGLz1TuuZAT6vkkX7_DbOWYYN33g3DPh2KlazCDFP4YqaB2sC3YlDTZ3oCSY6ePu2X8I82gQASDxBXskHZx9cja6Sd0FMyydc/s767/081020nam500mb09f09-mlcpe12f12_pvt_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="673" data-original-width="767" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgNXcO_eY8Z5Aq3LZKC4tyrPcVFKOQYsNpGmLy42Nui74FrGLz1TuuZAT6vkkX7_DbOWYYN33g3DPh2KlazCDFP4YqaB2sC3YlDTZ3oCSY6ePu2X8I82gQASDxBXskHZx9cja6Sd0FMyydc/s640/081020nam500mb09f09-mlcpe12f12_pvt_anno.jpg" width="640" /></a></div><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p>The inset on the graphic above is a forecast of mlCAPE valid at 7:00 am CDT, showing a long axis of instability extending eastward to Chicago, a corridor that would feed and maintain the convective complex and derecho as it evolved and moved eastward across several states during the morning and afternoon.</p><p>A similar situation accompanied a developing derecho that my wife Shawna and I experienced at Pierre SD in the early morning hours of 6/22/15, five years ago. Below is the surface map with the genesis region of the derecho indicated around Pierre at 1:00 AM CDT on 6/22/15:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgct3ux6uakkJ-amMj3o2Ickip0-_eNM_-9zTer5NDTRWS6GxrEU7xHjVFhaWBDcGRro8mEli437JRA3VPVbI8SRfLD5OqXH-lDL41gp7UCEbP0tmb74LJjeXIx0AYtn2fsKCSLCfn7bL22/s836/062215sfc06z_derecho_map.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="652" data-original-width="836" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgct3ux6uakkJ-amMj3o2Ickip0-_eNM_-9zTer5NDTRWS6GxrEU7xHjVFhaWBDcGRro8mEli437JRA3VPVbI8SRfLD5OqXH-lDL41gp7UCEbP0tmb74LJjeXIx0AYtn2fsKCSLCfn7bL22/s640/062215sfc06z_derecho_map.jpg" width="640" /></a></div><p><br /></p><p>Here is the RAP model sounding at Pierre SD at about the same time:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj8aInrlznOWTZlBLBECfg_zWiEMrgMBXIyNSWHfaW3Y5tsORJ7Zwyf-b1P9BdFrScnGLw64twbr9HkLJ5cvhPeBi-gl3-0NBC7stJvQi3qCDc0FhJFj1nnVyCFRWGKPVcOUhmQMSInVJuM/s713/062215pir07rapa_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="500" data-original-width="713" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj8aInrlznOWTZlBLBECfg_zWiEMrgMBXIyNSWHfaW3Y5tsORJ7Zwyf-b1P9BdFrScnGLw64twbr9HkLJ5cvhPeBi-gl3-0NBC7stJvQi3qCDc0FhJFj1nnVyCFRWGKPVcOUhmQMSInVJuM/s640/062215pir07rapa_anno.jpg" width="640" /></a></div><p><br /></p><p>Notice that the environment was similar to the 8/10/20 "genesis region" sounding shown earlier, with an elevated moist layer and sizable CAPE located _above_ a dry layer in the lowest 3 km. As new storms formed west of Pierre around midnight, evaporative cooling of rain through this dry layer resulted in the generation of very strong winds (120+ mph measured at Hayes SD!) that caused widespread damage in Pierre (including our motel) and locations eastward on 8/22/15 as the storms morphed into a derecho event.</p><p>Many derechos that initiate over the northern Plains and move eastward through the Midwest (the most common area for derechos in the U.S.) probably have this type of atmospheric setting in their genesis region. The drier air in the lowest 2-3 km below an elevated moist layer can result in rapidly-developing strong convective surface winds that spread eastward as a derecho along a west to east corridor of instability. </p><p>An important factor is the presence of a stationary or quasi-stationary west-east front (check out the surface maps earlier) with this axis of unstable air along it, helping to provide a corridor along which the recently-intiated derecho can intensify, spread, and maintain itself moving eastward. This was a key feature of Robert John's seminal work on derechos at SPC in the 1980's (see <a href="https://journals.ametsoc.org/waf/article/2/1/32/38564/Derechos-Widespread-Convectively-Induced" target="_blank">this paper</a>). Johns deserves much credit for making forecasters and meteorologists more aware of these dangerous convective systems.</p><p>Derechos are more complicated than this brief analysis would suggest. But I've touched on a few factors that are important for many warm season derechos across the Midwest.</p><p>- Jon Davies 8/13/20 </p>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com2tag:blogger.com,1999:blog-2399626414603781513.post-23806730836786152072020-08-02T14:10:00.009-07:002020-08-02T18:44:43.277-07:00A 'surprise' tornado on July 29, 2020 north of Kansas City - another subtle, marginal summer tornado setting<div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhDlO9dsLRkihtgrlwVQ6KZP4M7cvqbTHVlB6NjCS4Is99AUVZmflys_I-Q1F9le3Kky9ssbLALBE2DWB_HJtaCtMe0H750KLJ5SAuADO0tZxsK7Np4Hskdy2bf9om09DaXWvABP_V1blb_/s614/072920nwMOtor_derek.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="289" data-original-width="614" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhDlO9dsLRkihtgrlwVQ6KZP4M7cvqbTHVlB6NjCS4Is99AUVZmflys_I-Q1F9le3Kky9ssbLALBE2DWB_HJtaCtMe0H750KLJ5SAuADO0tZxsK7Np4Hskdy2bf9om09DaXWvABP_V1blb_/s0/072920nwMOtor_derek.jpg" /></a></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhf8TDnSzjAjh1DZ4XL2xz4Us7Ruv0RmVXpizZCa7PXz0bnckAOwuQMEv5pvbpRNbCDawZdyOrcLQCmN1UIbSSdLc11MLMMwktkrdacvbNVhShv7a74M5OWNGh4TDVet41QyClb7lOC5nxe/s477/072920nwMOtor_bc1_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="307" data-original-width="477" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhf8TDnSzjAjh1DZ4XL2xz4Us7Ruv0RmVXpizZCa7PXz0bnckAOwuQMEv5pvbpRNbCDawZdyOrcLQCmN1UIbSSdLc11MLMMwktkrdacvbNVhShv7a74M5OWNGh4TDVet41QyClb7lOC5nxe/s0/072920nwMOtor_bc1_anno.jpg" /></a></div><div class="separator" style="clear: both; text-align: center;"><br /></div>I've had several people ask me what was going on with the unexpected but well-photographed tornado (above, EF0) last Wednesday 7/29 at early afternoon near Smithville, MO, north of Kansas City, only a few mile north of where I live. I was quite surprised when I heard about the warning associated with it, and wondered myself how there could be a tornado on this particular day.</div><div><br /></div><div>Although not something one could really anticipate, a careful look back at the setting revealed that it was not 'random' or 'from out of the blue'.</div><div><br /></div><div>There was a well-defined boundary (dashed red-blue line below; a weak stationary front?) on the surface map at noon on 7/29/20 across the Kansas City metro area, delineating south winds to the south of the boundary from light easterly winds on the north side of it:</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjOSgQ1HGqyVem097BjgKs3OxXM6tFUHtGZ_6y8IG7INAZuJc1LsB6bUuekKLxppYg6Tj2R7p7S6NIU8PB6i5Ozt28OOOqiA1o1dX8pNaDSSzOUYkve-7ISQdZcChNRWGEMY0WkP1z4XxyK/s911/072920sfc1658_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="655" data-original-width="911" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjOSgQ1HGqyVem097BjgKs3OxXM6tFUHtGZ_6y8IG7INAZuJc1LsB6bUuekKLxppYg6Tj2R7p7S6NIU8PB6i5Ozt28OOOqiA1o1dX8pNaDSSzOUYkve-7ISQdZcChNRWGEMY0WkP1z4XxyK/s640/072920sfc1658_anno.jpg" width="640" /></a></div><div>As many forecasters and researchers have pointed out in recent years, tornadoes like boundaries, often because favorable wind shear (a change in wind direction and speed as winds veer with height) that might help generate a 'spin up' can be present along and across such boundaries. The black-circled 'S' on the map above shows that the location of the small supercell that later spawned the weak tornado was indeed very close to the boundary.</div><div><br /></div><div>Here's satellite and zoomed-in radar reflectivity near the time of the tornado (1:45 pm CDT, or 1845 UTC), with a white circle showing the location of the supercell mesocyclone and rotation in the storm near Smithville:</div><div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhvpnagQhs-7stBFLvn1gSXo_l8sZhJKIxHTvN-j7RVjgVepB0PNy5T2eLVsvGKB0dkqi6WzhuDpB3kE_GZ7imtLHPPNyAUPOAfkdeblVc8x9yxdC_5zg55_PgS5GIhEe0KAMWRjyIn6wyy/s804/072920sa-rdr1845_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="656" data-original-width="804" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhvpnagQhs-7stBFLvn1gSXo_l8sZhJKIxHTvN-j7RVjgVepB0PNy5T2eLVsvGKB0dkqi6WzhuDpB3kE_GZ7imtLHPPNyAUPOAfkdeblVc8x9yxdC_5zg55_PgS5GIhEe0KAMWRjyIn6wyy/s640/072920sa-rdr1845_anno.jpg" width="640" /></a></div></div><div>It is also interesting that a broad, weak low was present at 700 mb (roughly 10,000 ft above sea level) nearby over southeast Nebraska at midday on the SPC mesoanalysis:</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjCfXm8JdbfnpzLXtKIg30A1yV13hOAtmIMdUI8GuHFKjz1JOxaNhXD-9K9P0ztrEHLEy_BQHjps26-ErYZ-WPE6gQS6yb3TEwBrkBJM4DOvPM7i5CDhymSmVH0qqYnrTqu82wlZm8CWdsq/s554/072920spc700mb18_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="554" data-original-width="535" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjCfXm8JdbfnpzLXtKIg30A1yV13hOAtmIMdUI8GuHFKjz1JOxaNhXD-9K9P0ztrEHLEy_BQHjps26-ErYZ-WPE6gQS6yb3TEwBrkBJM4DOvPM7i5CDhymSmVH0qqYnrTqu82wlZm8CWdsq/s0/072920spc700mb18_anno.jpg" /></a></div><div>This weak low aloft and a short wave trough (heavy black dashed line) moving around it helped provide lift for generating thunderstorms over northeast Kansas and northwest Missouri. In a way, this looked like a weak <a href="http://davieswx.blogspot.com/2020/04/april-22-2020-tornadoes-in-southern.html" target="_blank">'cold-core' tornado setting</a>, and coupled with the east-west surface boundary, was another factor that may have helped set the stage for a tornado.</div><div><br /></div><div>The storm environment, though subtle, also offered some ingredients that were marginally supportive of supercell tornadoes. The first panel below from the SPC mesoanalysis at 1800 UTC (noon CDT) showed that low-level wind shear, though not large, was enhanced some just north of the east-west boundary (0-1 km storm-relative helicity / SRH > 50 m2/s2), as one might expect with easterly surface winds just north of Kansas City on the surface map earlier:</div><div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj1prbuz3xKFjszjj9TvlMT5a4iEE_lOEu62hAiSawR4rqeVw4LtQNu94uRYTnWwGbgq9owzRY_dWke_-EleHZ6TN5H7xDiAuN0sAsO5uMiRXHAwOuYGQk6WgRf8rY_KJzA5XwYCAzbWP0W/s884/072920spc_srh1-cp3-06s18_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="364" data-original-width="884" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj1prbuz3xKFjszjj9TvlMT5a4iEE_lOEu62hAiSawR4rqeVw4LtQNu94uRYTnWwGbgq9owzRY_dWke_-EleHZ6TN5H7xDiAuN0sAsO5uMiRXHAwOuYGQk6WgRf8rY_KJzA5XwYCAzbWP0W/s640/072920spc_srh1-cp3-06s18_anno.jpg" width="640" /></a></div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div>The 2nd panel above showed that instability in low-levels close to the ground was large (0-3 km mlCAPE > 150 J/kg) near the boundary across the Kansas City area. Although subtle, combinations of both low-level shear and instability together were largest in that area (see black oval in 1st and 2nd panels above), just south of Smithville.</div><div><br /></div><div>One last ingredient was deep-layer wind shear (surface to 6 km above ground, 3rd panel above) that was near the lower limit (around 25 kt) of what is considered supportive for supercell storms. But on this day it was enough to do the trick.</div><div><br /></div><div>Here's a RAP model analysis sounding estimate of the environment near Smithville at midday along the east-west boundary:</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh8p0Gt7ZnjK1lrdYuAAniI4Z9o81CPX3B5Pc3QmIc-xMldrTOTxaHYw3IXswPQ4kN-G19tvKIsx0heJpRP8Rc0P9u2t-m3N-kVyr4_Kn06YNbt02gzI_LULo4ABVMY6X63kL_tn3oMdeP8/s1194/072920smithvilleMO18rapa_cod_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="781" data-original-width="1194" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh8p0Gt7ZnjK1lrdYuAAniI4Z9o81CPX3B5Pc3QmIc-xMldrTOTxaHYw3IXswPQ4kN-G19tvKIsx0heJpRP8Rc0P9u2t-m3N-kVyr4_Kn06YNbt02gzI_LULo4ABVMY6X63kL_tn3oMdeP8/s640/072920smithvilleMO18rapa_cod_anno.jpg" width="640" /></a></div><div><br /></div><div>Although not impressive, the instability (which I've manually shaded in red above) and vertical wind shear were apparently just enough to help generate and support a tornado as the supercell crossed the surface boundary moving north-northeast. </div><div><br /></div><div>In particular, the instability in lowest levels close to the ground probably helped with stretching of air in the small storm's updraft as it interacted with the local boundary. The photo below shows a cloud ridge flowing into the storm with 'vapory-looking' scud close to the ground, a typical visual 'look' when large amounts of low-level CAPE are present not far above ground, and low-level stretching in updrafts may be enhanced.</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgRvFctFIkVvRJlGcCOjGbCJiiRgL54DFoBHx41H_QPUnfzgS8I0MJkM4UnY9AxobRCT0DHT-D7YbgS0mmwWmC0cwn9FdaIWM_6f5ff43g7SJiXJLkn4_Wdfa4V9TzGnnsVykDCT4xFu5RZ/s608/072920nwMOsprcl_jl2_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="346" data-original-width="608" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgRvFctFIkVvRJlGcCOjGbCJiiRgL54DFoBHx41H_QPUnfzgS8I0MJkM4UnY9AxobRCT0DHT-D7YbgS0mmwWmC0cwn9FdaIWM_6f5ff43g7SJiXJLkn4_Wdfa4V9TzGnnsVykDCT4xFu5RZ/s0/072920nwMOsprcl_jl2_anno.jpg" /></a></div><div><br /></div><div>This weak event wasn't of much importance (brief tornado, no damage), but is another illustration of how subtle ingredients can come together to produce a mesoscale 'accident'. Given how marginal the setup was, an experienced nowcaster and meteorologist would not expect anything more than a weak tornado or two from such a setting.</div><div><br /></div><div>- Jon Davies 8/2/20</div>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com0tag:blogger.com,1999:blog-2399626414603781513.post-8684882746689184662020-07-16T11:59:00.007-07:002020-07-16T12:35:01.468-07:00EF4 tornado in Minnesota on July 8, 2020 - a rather subtle environment for a violent tornado <div class="separator" style="clear: both; text-align: center;">
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After four EF4 tornadoes in April (3 in Mississippi, 1 in South Carolina), there were none in the U.S. in May and June. But on July 8 in west-central Minnesota (MN), an EF4 tornado (images above) near Dalton, MN shortly after 5:00 pm CDT (2200 UTC) killed one person. This was the first violent tornado in July in the U.S. since 2004!<br />
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The environment at first glance did not appear likely to generate a violent tornado, as low-level wind shear (storm-relative helicity, or SRH) wasn't notably large. But there was a boundary in the area and large instability (CAPE), along with enough deep-layer wind shear to support tornadic supercells. Here's a look at the setting...<br />
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SPC mesoanalysis graphics at 2200 UTC (5:00 pm CDT) showed large total CAPE (mlCAPE > 4000 J/kg, 1st panel below) near the soon-to-be tornadic storm that had developed during the previous hour in west-central MN:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj3gzKbTRk7myu2ryAtL7fTXx1N7PAUbLny-6PpS5vUVLX8G7I9JRn_XlJrLkU33kleOz_Stc1Oot5KPa_H0Xf3tQbqm-iIna2rHbcyePJT_udaSSlNnAbhRfoZj64bWQJ58Q18TKPSDXv0/s1600/070820spc_mlcpe-06s22_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="436" data-original-width="580" height="480" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj3gzKbTRk7myu2ryAtL7fTXx1N7PAUbLny-6PpS5vUVLX8G7I9JRn_XlJrLkU33kleOz_Stc1Oot5KPa_H0Xf3tQbqm-iIna2rHbcyePJT_udaSSlNnAbhRfoZj64bWQJ58Q18TKPSDXv0/s640/070820spc_mlcpe-06s22_anno.jpg" width="640" /></a></div>
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Deep-layer shear (2nd panel above) was enough (30-40 kt) to help organize the isolated cell into a supercell. Just as important, the cell developed near an east-west boundary (warm front /stationary front, also shown on the graphics above) that extended eastward from a surface low, a favorable setting for tornadoes when the surrounding environment offers additional support.<br />
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Also at 2200 UTC, low-level instability (0-3 km mlCAPE) was large over west-central MN (> 125 J/kg, 1st panel below), although 0-1 km SRH was nothing that would raise eyebrows much (0-1 km SRH 75-100 m2/s2, 2nd panel below):<br />
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But together, the combination of just enough low-level shear/SRH with strong low-level and total CAPE in the vicinity of the east-west boundary east of the surface low was more favorable for tornado potential than a look at wind shear parameters alone might suggest.<br />
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In fact, supercell and tornado development was rather fast and 'explosive', as seen in the two satellite images below:<br />
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In just less than an hour from initiation, the storm became a supercell and planted a strong/violent tornado on the ground. That's quite fast compared to many supercells that take two hours or more to produce tornadoes.<br />
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A contributing factor to this rapid development may have been low-level lapse rates (below), not shown in the SPC graphics above:<br />
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The axis of red dots in the graphic above shows strong surface heating extending from the southwest into the supercell's environment near the boundary over west-central MN. Such steep lapse rates (> 7.0 degrees C per km, a rapid change in temperature above ground) can enhance the stretching of low-level air entering storm updrafts, adding a 'kick' to an already unstable situation and helping to make the most of available low-level wind shear (SRH) as it tilts and stretches into an updraft.<br />
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Back around 2005, I came up with a parameter called 'enhanced stretching potential' (ESP) that combined low-level lapse rates with low-level CAPE to help locate areas that might have this extra 'kick'. It was designed mainly for diagnosing short-term potential for landspout tornadoes along sharp boundaries (see <a href="https://pdfs.semanticscholar.org/b878/c75ba13ea93ee9cecab25e245d82563e6abb.pdf">this paper</a>). But on 7/8/20, ESP overlapped the area we discussed above that already had potential for tornadoes suggested by more typical supercell tornado parameters:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmIh8CmX-0enhShYwMIfi0JuwBEuLYrPA_wx4-9Hb2Ce1W7AknC3ETnc1BhDL6VYxY3UlH9noednXLcTKi0PWgYoFnd8Em2zDO7xLTb1dd6pZ7SfGUZJhlroymHZjGESR4EwwAvyP-kTtj/s1600/070820spc_esp22_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="469" data-original-width="487" height="385" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmIh8CmX-0enhShYwMIfi0JuwBEuLYrPA_wx4-9Hb2Ce1W7AknC3ETnc1BhDL6VYxY3UlH9noednXLcTKi0PWgYoFnd8Em2zDO7xLTb1dd6pZ7SfGUZJhlroymHZjGESR4EwwAvyP-kTtj/s400/070820spc_esp22_anno.jpg" width="400" /></a></div>
It may have added some 'gasoline' to the fire in this case, speeding up supercell and tornado development. But that's only speculative. I will mention that the prolific tornadic supercell in southern Saskatchewan (Canada) on July 4 that I touched on in my <a href="http://davieswx.blogspot.com/2020/07/unusual-ef2-tornado-in-south-dakota-on.html">previous post</a> had some of the same ingredients (SRH < 100 m2/s2, large CAPE and large ESP, as well as an east-west boundary; not shown).<br />
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As ESP was originally intended for highlighting short-term possibility for landspouts, it is worth noting on 7/8/20 that the ESP graphic above showed an ESP maximum over north-central Nebraska, where landspouts did occur later that evening along a boundary southwest of a storm near Thedford, Nebraska:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj6CpcryfDPnCUIoNdgwRYU7FCP0sHTCOhdAa4VYj6Hq-KSk8Rv7Vq02zsenCgn77yIODg3eSvmr_NAgGoKzWPUP4WmpBLK9kq8Tdb-k8k6Awb-dDirxe32pc9RbUpgi2KnQxgcq7qqyl4e/s1600/070820ncNElndspt_ja3-ja4_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="724" data-original-width="966" height="298" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj6CpcryfDPnCUIoNdgwRYU7FCP0sHTCOhdAa4VYj6Hq-KSk8Rv7Vq02zsenCgn77yIODg3eSvmr_NAgGoKzWPUP4WmpBLK9kq8Tdb-k8k6Awb-dDirxe32pc9RbUpgi2KnQxgcq7qqyl4e/s400/070820ncNElndspt_ja3-ja4_anno.jpg" width="400" /></a></div>
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And other landspouts occurred on 7/8/20 along a boundary and boundary intersection over northeast Colorado where ESP was also large (not shown).<br />
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Finally, here's the large-scale NAM model 500 mb forecast for mid-afternoon on 7/8/20 showing the strong shortwave disturbance (red dashed line) in mid-levels moving through the northern plains that helped intiate the tornadic supercell in MN:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiY4H8O9jNZ9HM98owgIk6YFOCnQxFqki8I6TymacIeVl3mcr4TVVEWc5pPnENvFoYAYLgNfrtPL44QWJK_UFwsTaWtk23ptKzZHloJB5_4L797EXzsqfawvXQ6cx76eEG0dqpax5h03FWj/s1600/070820nam500mb21f09_pvt_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="758" data-original-width="666" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiY4H8O9jNZ9HM98owgIk6YFOCnQxFqki8I6TymacIeVl3mcr4TVVEWc5pPnENvFoYAYLgNfrtPL44QWJK_UFwsTaWtk23ptKzZHloJB5_4L797EXzsqfawvXQ6cx76eEG0dqpax5h03FWj/s640/070820nam500mb21f09_pvt_anno.jpg" width="561" /></a></div>
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It is interesing that the early half of July 2020 has been more active for tornadoes in the central and northern Plains of the U.S. than in the last half of June.<br />
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- Jon Davies 7/16/20</div>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com0tag:blogger.com,1999:blog-2399626414603781513.post-86624725805629156772020-07-06T12:46:00.019-07:002020-07-16T12:25:18.948-07:00Unusual EF2 tornado in South Dakota on July 4, 2020 is 1st strong tornado in U.S. since June 10<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjxh_cysKYG-_9oLLmmYYjphqBinchixgydG4QtLQ4lgvPPRrLon30RQYkbTCxIQB-QPW6AVsMOBhSkIS7zc7xUZZ2S1UXFL0DXdQYUHnhQJBjzOvZ0itQZjNkyx8nXsFJKj5qRPZAiAMnC/s876/070420sSKCNtor_jb_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="608" data-original-width="876" height="435" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjxh_cysKYG-_9oLLmmYYjphqBinchixgydG4QtLQ4lgvPPRrLon30RQYkbTCxIQB-QPW6AVsMOBhSkIS7zc7xUZZ2S1UXFL0DXdQYUHnhQJBjzOvZ0itQZjNkyx8nXsFJKj5qRPZAiAMnC/w625-h435/070420sSKCNtor_jb_anno.jpg" width="625" /></a></div><div><br /></div>July 4th was a rather active day in the northern Plains of the U.S. and southern Canada. In particular, a photogenic supercell with a sequence of tornadoes occurred in southern Saskatchewan on July 4 (see photo above). This blog post isn't about that supercell, but I will discuss it briefly at the end here.<br /><div><br /></div><div>What I do want to focus on is a tornado (rated EF2) northwest of Aberdeen in South Dakota near the town of Wetonka, around the time that the tornado pictured above was happening in Canada. The South Dakota tornado was the first significant tornado in the U.S. since June 10th, a surprising 25-day streak during a late spring / early summer period that has seen below normal tornado activity in 2020. </div><div><br /></div><div>**** UPDATE Note: NWS Cheyenne WY was slow in rating an EF2 tornado northwest of Hemingford, Nebraska on July 2, 2020. Now with that new information, I make the correction that the Nebraska tornado on 7/2/20 was the first significant tornado in the U.S. since June 10. ****<br />
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The Wetonka, South Dakota tornado came from this supercell, shown around an hour before the tornado:<br /><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgwbOxNPyVk9pTJ8JUbBw6VB7QowJs8MCpJ7iQnR0IM3gCf-EtN-caarSEheshtqOv8iQsAHA0aI6DQg8xfFYQBEHqdBUNHtJlsN7MW-6H7nDCraAD0NX4_8yJ3J3uJNkRWs_B3u5yi__w_/s658/070420ncSDsprcl_qv_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="421" data-original-width="658" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgwbOxNPyVk9pTJ8JUbBw6VB7QowJs8MCpJ7iQnR0IM3gCf-EtN-caarSEheshtqOv8iQsAHA0aI6DQg8xfFYQBEHqdBUNHtJlsN7MW-6H7nDCraAD0NX4_8yJ3J3uJNkRWs_B3u5yi__w_/w500-h320/070420ncSDsprcl_qv_anno.jpg" width="500" /></a></div><div>
I wanted to document that the evolution of the supercell and its associated outflow boundary before the tornado was something you don't see that often.<br />
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Below is a 3-panel base reflectivity sequence during the 30 minutes prior to the tornado. Notice the outflow boundary (fine blue line) ahead of it:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEidqWnzx7aM9gPfOQZEAj75Ql6hHm29p_0EOCQnF3VExdI1uQJGfbYz7l7-s_cvEeHpTHOxGLUNQVuVLkouzGrE5By8-0PuxOm1v9vFnhqFsGRPLP0SbXMqH5dANjyJvlqfVKpimEzK55Is/s1600/070520rd0001-0014-0026abr_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="527" data-original-width="1204" height="280" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEidqWnzx7aM9gPfOQZEAj75Ql6hHm29p_0EOCQnF3VExdI1uQJGfbYz7l7-s_cvEeHpTHOxGLUNQVuVLkouzGrE5By8-0PuxOm1v9vFnhqFsGRPLP0SbXMqH5dANjyJvlqfVKpimEzK55Is/s640/070520rd0001-0014-0026abr_anno.jpg" width="640" /></a></div>
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This outflow surged out southeast in front of the storm in the hour before the tornado, suggesting that the supercell was "outflow-dominant" (rain-cooled air moving outward from the storm), usually signaling to meteorologists and storm spotters that tornado development is unlikely. In other words, the cool outflow air would undercut the storm updraft beneath which a tornado might form.<br />
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However, in this case, the outflow <i><b>_slowed_</b></i> and the rotating supercell storm caught up to it, pulling and wrapping the outflow boundary back in under the storm and updraft. At the white arrow in the radar images above, see the fine blue line slow and then curl back northwest into the supercell as a 'hook-shaped' echo forms (see last panel above at 7:27 pm CDT), allowing the supercell updraft to access warm moist inflow air at the surface. This was likely an important factor in the storm's ability to produce a tornado.<br />
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The zoomed-in radar image below is during the tornado moving southeastward near Wetonka. The circle indicates the supercell mesocyclone where the tornado was located, and I've also indicated with a dashed white line the boundary and inflow wrapping way back into the mesocyclone from the east during the tornado.<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiFIGAUhS2tpKDZBPUPMdG0jSUQxxft9uqvy19cDIcjRKM1A9lFj5J92IWgAsCSnybujVm3TuKQyZYWyIMNZaR0AWNWO-e29M1LflJ4Nodp4SsaVLVGZA7Z6vbA6SgFIohO4aPfKQglIvUV/s1600/070520rdr0037abr_zoom_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="620" data-original-width="441" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiFIGAUhS2tpKDZBPUPMdG0jSUQxxft9uqvy19cDIcjRKM1A9lFj5J92IWgAsCSnybujVm3TuKQyZYWyIMNZaR0AWNWO-e29M1LflJ4Nodp4SsaVLVGZA7Z6vbA6SgFIohO4aPfKQglIvUV/s640/070520rdr0037abr_zoom_anno.jpg" width="452" /></a></div>
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As seen in the earlier radar sequence, outflow initially surging out ahead of the storm was probably a reason why the storm was not tornado-warned, only severe-warned. Typically, once a supercell becomes outflow-dominant, it remains that way, unlike this case. It is somewhat unusual to see an outflow boundary out ahead of a storm get pulled back in underneath it, suggesting that the supercell mesocyclone on July 4 was rather strong, while at the same time the initial outflow air in advance of it was modifying and weakening. <br />
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From the radar images above, it appears the supercell mesocyclone was largely wrapped in rain, a probable reason why there are no photos of the tornado from local residents near Wetonka.<br />
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The storm environment, while not remarkable, was certainly supportive of supercell tornadoes. The SPC mesoanlysis graphic below shows that the effective-layer significant tornado parameter was maximized over north-central South Dakota in the vicinity of the supercell:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgUBpX5JpkiH3Ardw2nq684JKBOoTZm3THGGeg8xO8dRUZ2VTAVMTcmba6OVeEMtYeOOvWI0bP6YwE-8lFDft36dh6dnERE19rgXnNbrljL8kwqVWCrSdxAUiikKP1xo2sPzhOWvlozZx3x/s1600/070520spcstpc00_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="590" data-original-width="771" height="488" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgUBpX5JpkiH3Ardw2nq684JKBOoTZm3THGGeg8xO8dRUZ2VTAVMTcmba6OVeEMtYeOOvWI0bP6YwE-8lFDft36dh6dnERE19rgXnNbrljL8kwqVWCrSdxAUiikKP1xo2sPzhOWvlozZx3x/s640/070520spcstpc00_anno.jpg" width="640" /></a></div>
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Also, here is a RAP model sounding (below) from a point just south-southwest of the supercell at 7:00 pm CDT, about a half hour before the tornado:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgF6-GuB2AZSHRKKHgvyiDh5Mlwuq1D9mDfLJtr8FJCgaFK2cuILBSaRz7i7QbbuvPNoiynKPxDnDb1hWgesyM6G1lUuu5J5Ty4-Ijl4NaOIKxop_QiHPbu-uAQzG4FrVj2FNjFdP8P3dHs/s1600/070520hosmerSD00rapa_cod_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="780" data-original-width="1188" height="420" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgF6-GuB2AZSHRKKHgvyiDh5Mlwuq1D9mDfLJtr8FJCgaFK2cuILBSaRz7i7QbbuvPNoiynKPxDnDb1hWgesyM6G1lUuu5J5Ty4-Ijl4NaOIKxop_QiHPbu-uAQzG4FrVj2FNjFdP8P3dHs/s640/070520hosmerSD00rapa_cod_anno.jpg" width="640" /></a></div>
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<br /><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div>Low-level wind shear was just enough (storm-relative helicity or SRH near 100 m2/s2) with a looping low-level wind profile, and over 30 knots of deep-layer wind shear was also present. Total mixed-layer CAPE was large (> 3500 J/kg), and low-level mlCAPE was also significant (0-3 km mlCAPE around 140 J/kg). This latter ingredient, along with the available low-level wind shear, would likely facilitate low-level stretching and 'spin' to help generate a tornado, <i>_<u><b>if</b></u>_</i> a rotating storm could access the unstable inflow air ahead of it's own outflow.</div><div>
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Again, this was something of an unusual case in that the storm was able to pull its own outflow boundary (initially surging southeast) back in underneath its updraft to access the unstable warm sector inflow air necessary to support the formation of a tornado.<br />
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This suggests that meteorologists and storm chasers should remain alert to the possibility of slowing outflow that might allow a supercell to catch up to its leading edge and reconfigure the storm's outflow boundary underneath it. </div><div><br /></div><div>Now, let's go back to the Saskatchewan supercell I mentioned at the top. It moved east-southeast along a wind shift boundary marked by the dashed red-blue line in the satellite image below at 0016 UTC:</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjdTsBm7EsaJPE3gOJGPQcBIZFIV5kMHj4mHGEBjDRKZtbrSWDguBG0n6YqSA7UCHugTRZtbord67JJFKJ-z_EQD_rgUSpziofe8Oa4botiwFuipJMh9ffdToZAWQ_DH7V-yrIA9TH517MF/s821/070520sat0016_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="657" data-original-width="821" height="500" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjdTsBm7EsaJPE3gOJGPQcBIZFIV5kMHj4mHGEBjDRKZtbrSWDguBG0n6YqSA7UCHugTRZtbord67JJFKJ-z_EQD_rgUSpziofe8Oa4botiwFuipJMh9ffdToZAWQ_DH7V-yrIA9TH517MF/w625-h500/070520sat0016_anno.jpg" width="625" /></a></div><div class="separator" style="clear: both; text-align: center;"><br /></div><div class="separator" style="clear: both; text-align: left;">This supercell produced three tornadoes as it moved along this boundary, but thankfully all were in open country. </div><div class="separator" style="clear: both; text-align: left;"><br /></div><div class="separator" style="clear: both; text-align: left;">What's interesting about this supercell is that it appeared to produce tornadoes in an environment with rather high lifting condensation level (LCL) heights (1750-2000 m above ground), as seen below in the 00 UTC 7/5/20 SPC mesoanalysis:</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhVrs431dGN3zYNzY2DmYbIXRe6KbPI99e1KQ1B5VrCYRWiwpAnm4PJVNqwB4X0CIXwApLeJZywxALDe-FBMQ1SixIvhTsxiK1C8GoR5lttxCk-iAtpTyiBIWufwq3UflrjPu9XyycEQ9P1/s643/070520spc-mllcl-cp3_00z_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="373" data-original-width="643" height="364" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhVrs431dGN3zYNzY2DmYbIXRe6KbPI99e1KQ1B5VrCYRWiwpAnm4PJVNqwB4X0CIXwApLeJZywxALDe-FBMQ1SixIvhTsxiK1C8GoR5lttxCk-iAtpTyiBIWufwq3UflrjPu9XyycEQ9P1/w625-h364/070520spc-mllcl-cp3_00z_anno.jpg" width="625" /></a></div><div class="separator" style="clear: both; text-align: left;"><br /></div><div class="separator" style="clear: both; text-align: left;">It also appeared to occur in a setting with little low-level wind shear (SRH < 50 m2/s2, not shown). These factors are generally negatives for supercell tornado potential. </div><div class="separator" style="clear: both; text-align: left;"><br /></div><div class="separator" style="clear: both; text-align: left;">However, the tornadic Canadian cell did occur in an area of enhanced low-level CAPE (see 2nd SPC panel above), which could enhance low-level stretching, as well as enhanced surface vortcity (light blue lines in 2nd panel, a source for 'spin') near the aforementioned boundary. Low-level lapse rates were also steep along this boundary (near 9.0 deg C, not shown), which could help with low-level stretching. </div><div class="separator" style="clear: both; text-align: left;"><br /></div><div class="separator" style="clear: both; text-align: left;">These ingredients together suggest that there may have been some non-supercell processes contributing to this Canadian tornado event, in addition to supercell processes (see my prior blog post <a href="http://davieswx.blogspot.com/2020/06/a-look-landspout-tornado-formation-in.html" target="_blank">here</a>). But that's speculative, because the SPC data is at the edge of the SPC mesoanalysis and RAP model domain, which could affect the accuracy of soundings and parameters. Still, this Canadian case deserves some further study.</div><div class="separator" style="clear: both; text-align: left;"> </div><div class="separator" style="clear: both;">So, even in a slow tornado year, there are definitely interesting cases to examine!</div><div>
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- Jon Davies 7/6/20<br />
</div></div>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com0tag:blogger.com,1999:blog-2399626414603781513.post-38448524112031622812020-06-25T11:34:00.023-07:002020-06-25T12:11:00.024-07:00A look at landspout tornado formation in northwest Kansas on June 21, 2020<div class="separator" style="clear: both; text-align: center;">
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I've heard quite a few chasers "complaining" :-) about the lack of tornadoes in May & June 2020 over the central Plains. That dearth of significant tornadoes is actually a _good_ thing, because they obviously can kill and injure people and turn lives upside down. But I do sympathize with chasers who have a desire to see tornadic storms out in open country where damage is minimized. <br />
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I haven't done a blog post since mid May (life has been busy on several fronts). So, with the relative lack of Plains tornadoes in 2020, I thought I'd write something about last Sunday's (6/21/20) landspout tornado in northwest Kansas west of Hill City (see images above). It's also interesting to look at how a day that appeared somewhat promising to many chasers for supercells and possible tornadoes in west-central Kansas didn't pan out very well.<br />
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First, the landspout tornado. These are not really forecast-able, as they are the result of mesoscale "accidents" where ingredients (a sharp slow-moving boundary with instability and steep low-level lapse rates in the area and a storm intensifying right over that boundary) have to come together just right. But in the one to three hours leading up to such an event, it may on occasion be possible to see some of those ingredients coming together.<br />
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Here's the surface map over Kansas at 2:00 pm CDT:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhxtL5_jg_FVX26ps9L34QU4J8Kim6BuaV1eP3oQPdrwJwbZmYaC6tsuDrBa76qQlpokv-bvJbpi0lesXPJf7H7sPnDDHl-LS6MLVjTZw4TfPMncXQch4dIUvTiH1wnqHvfu9N1bqJqEnBg/s1600/062120sfc1858_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="554" data-original-width="467" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhxtL5_jg_FVX26ps9L34QU4J8Kim6BuaV1eP3oQPdrwJwbZmYaC6tsuDrBa76qQlpokv-bvJbpi0lesXPJf7H7sPnDDHl-LS6MLVjTZw4TfPMncXQch4dIUvTiH1wnqHvfu9N1bqJqEnBg/s640/062120sfc1858_anno.jpg" width="538" /></a></div>
Note the wind shift boundary (a weak stationary front) over northwest Kansas west and northwest of Hill City. This boundary was close enough to Goodland's radar that it could be seen as a fine line (see white arrows on lowest elevation base reflectivity images below) as storms built rapidly in the Oakley area ahead of the boundary at early to mid afternoon:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi1jD9KTfJyQ7_eWTvEh6eOAPdiBbaBqwzShv_SWMPz-3_zt92SdhpbhgGEES66AdiDDW_AIBMCzNWQWAV6Am8Dw_zxGDUexcB0Fju3wLgpbGg6i5eL-neOSBSKP55-QEwLfcKzM3gUtowc/s1600/062120rd1922-1944-1948gld_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="637" data-original-width="1304" height="312" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi1jD9KTfJyQ7_eWTvEh6eOAPdiBbaBqwzShv_SWMPz-3_zt92SdhpbhgGEES66AdiDDW_AIBMCzNWQWAV6Am8Dw_zxGDUexcB0Fju3wLgpbGg6i5eL-neOSBSKP55-QEwLfcKzM3gUtowc/s640/062120rd1922-1944-1948gld_anno.jpg" width="640" /></a></div>
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Notice on the radar images at 1944 and 1948 UTC (2:44 pm and 2:48 pm CDT) how the boundary began to bow northwestward in response to outflow from the rapidly developing storms to the southeast. However, the same boundary on its northern end stayed largely stationary in place near Hoxie (HOX) and west of Hill CIty (HLC), and a cell formed quickly right over this segment of the boundary in the 1944-1922 UTC time frame, indicated on the last two panels of the radar above. <br />
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This is the cell that produced the landspout tornado roughly 1950-2005 UTC (2:50 pm to 3:05 pm CDT) northeast of Hoxie and west of Hill City. Contributing ingredients were the storm forming right over the boundary in an environment with large CAPE and steep low-level lapse rates (> 9.0 deg C in the lowest 3 km above ground, see RAP model 1-hour forecast sounding for Hill City at 1900 UTC / 2:00 pm CDT below) to enhance stretching of vertical vorticity on the boundary:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiwuVT6fnUMQ3fuE_EfQaZPvOdzzsSQ35RtyAjykkdItu0uBl183zgjT9LJUVnN9u0VZJlz9zdXiy-h4A-j6acd5Nmp0vjv1Lka4Gy16nPSYgn5BtmjVQbPzubGRvoL5mKQwrEFdrxOdTsf/s1600/062120hlc19rapf01_cod_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="780" data-original-width="1190" height="418" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiwuVT6fnUMQ3fuE_EfQaZPvOdzzsSQ35RtyAjykkdItu0uBl183zgjT9LJUVnN9u0VZJlz9zdXiy-h4A-j6acd5Nmp0vjv1Lka4Gy16nPSYgn5BtmjVQbPzubGRvoL5mKQwrEFdrxOdTsf/s640/062120hlc19rapf01_cod_anno.jpg" width="640" /></a></div>
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It also helped that this segment of the boundary was somewhat removed from the spreading outflow from the storms farther to the south and southwest (see radar graphic earlier).<br />
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I've always found landspouts fascinating as an alternative way to generate tornadoes without the horizontal wind shear (storm-relative helicity or SRH) needed for most supercell tornadoes. Indeed, there was very little low-level wind shear early Sunday afternoon 6/21/20 in northwest Kansas (see the sounding above). In this case, the vorticity (source of "spin") for the non-supercell tornado (landspout) came directly from the boundary.<br />
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Regarding the potential for long-lived supercells and supercell tornadoes on 6/21/20, it turns out the models from that morning were not very encouraging over west-central Kansas. We'll look at that next.<br />
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Below is the NAM 9-hour 500 mb forecast for mid-afternoon showing a short wave disturance approaching from the northwest providing upward motion to fire up storms rapidly in an unstable environment over western Kansas. Note that winds in mid-levels weren't that strong (only 20-25 kt):<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiQXsMccEjilCOCw0cJ6T47BwBPX1rESIFUscUUqixjsGLPiHOceN1DKupl1Mljy425DBlMb_SF0al1HCxI3emN2941b4B_rf6tcxRvZj88k6M4F60JPRSpDTmKEHpBQTux0l7dz26tWDgL/s1600/062120nam500mb21f09_pvt_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="760" data-original-width="708" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiQXsMccEjilCOCw0cJ6T47BwBPX1rESIFUscUUqixjsGLPiHOceN1DKupl1Mljy425DBlMb_SF0al1HCxI3emN2941b4B_rf6tcxRvZj88k6M4F60JPRSpDTmKEHpBQTux0l7dz26tWDgL/s400/062120nam500mb21f09_pvt_anno.jpg" width="372" /></a></div>
This flow aloft was enough to marginally support organized storms and supercells, but if storms developed rapidly over a large area, a pool of outflow air would probably undercut any supercells and make them short-lived as a squall line formed.<div><br /></div><div>Also below are the 9-hour NAM forecasts of mixed-layer CAPE, 0-1 km SRH, and surface-based lifting condensation level (LCL) heights valid at mid afternoon:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhfs8M712nXlkCptDXCyYzl-8_6kReOUsYRtqC2uAE70NcLXyVVsugrEQGgQ_UeQicFDMOFRwiXldRH6xyZuCjisvTEpQ69afYpsKmofvQ0NqDqmVdt-ccSwO8nNr71Sjpj1aS7dhRhHEZi/s1600/062120nam_mlcpe-srh1-sblcl21f09_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="457" data-original-width="977" height="298" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhfs8M712nXlkCptDXCyYzl-8_6kReOUsYRtqC2uAE70NcLXyVVsugrEQGgQ_UeQicFDMOFRwiXldRH6xyZuCjisvTEpQ69afYpsKmofvQ0NqDqmVdt-ccSwO8nNr71Sjpj1aS7dhRhHEZi/s640/062120nam_mlcpe-srh1-sblcl21f09_anno.jpg" width="640" /></a></div>
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<br /><br /><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div><br /></div><div>Notice that, although forecast CAPE was large, 0-1 km SRH was very much lacking (as noted earlier), and in particular, LCL heights were all quite high (> 1500-2000 m above ground). Such high-based storms (LCL is an estimate of cloud base height) with rain passing through a relatively deep layer of unsaturated air below cloud base would result in evaporational cooling and enhanced cool outflow. Indeed, although there was a short-lived supercell north of Dodge City around 4:00 pm CDT, cold outflow from the expanding cluster of storms over west-central Kansas at mid-afternoon began to race south, destroying the potential for discrete supercells and short-lived supercell tornadoes (see the photo below as storms were gusting out into a squall line near Dodge City):</div><div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjJDxKX1nFRfHKWcSSCNce3GJZEN7I_MgJ2K_cyKpKAcSfT5tL8m34da8B3V9AxphwySIZRCelEKJVJ3SxB6cPtmRQQsA9zmRgTdxjn9gL4Nq9WH8s8a_4ODVKOOpvfjBq2q4_vr6j8aGAi/s1600/062120swKSstm_nl_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="339" data-original-width="605" height="223" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjJDxKX1nFRfHKWcSSCNce3GJZEN7I_MgJ2K_cyKpKAcSfT5tL8m34da8B3V9AxphwySIZRCelEKJVJ3SxB6cPtmRQQsA9zmRgTdxjn9gL4Nq9WH8s8a_4ODVKOOpvfjBq2q4_vr6j8aGAi/s400/062120swKSstm_nl_anno.jpg" width="400" /></a></div>
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Some strong wind gusts were recorded in the Dodge City area and other parts of southwest and south-central Kansas as the storm cluster lined out and moved southward. </div><div><br /></div><div>Key ingredients suggesting that this would be more of a "gust-out" event instead of supercells and tornadoes over west-central Kansas were:</div><div><span> 1) High LCL heights to encourage evaporative cooling and strong outflow from storm clusters</span></div><div><span><span> 2) Lack of low-level wind shear, reducing potential for low-level rotation in early discrete cells</span></span></div><div><span><span> 3) Relatively marginal wind fields in mid-levels such that early supercells could not become well-organized and established</span></span> </div><div><br /></div><div>The landspout tornado in northwest Kansas came from non-supercell / non-mesocyclone processes before outflow began to dominate from expanding storm clusters.<br />
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All photos in this blog post are from various posts on Twitter made by local people and chasers last Sunday as I watched this event unfold from home in Kansas City.<br />
<br />Shawna and I have been able to chase a couple low-end but interesting cold-core tornado events this spring. I'll try to post something about those in July as I get time.<br />
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- Jon Davies 6/25/20<br />
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</div></div>Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com7tag:blogger.com,1999:blog-2399626414603781513.post-88205975973333355942020-05-17T08:04:00.012-07:002020-05-18T07:52:40.141-07:00May 14, 2020 tornadoes in the Flint Hills: A late start to Kansas' 2020 tornado season.<div class="separator" style="clear: both; text-align: center;">
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Systems coming through the central Plains the first half of May have been generally unimpressive, but last Thursday's setting suggested at least a chance of supercells and maybe a brief tornado in east-central Kansas (KS). This potential was relatively close to Kansas City, requiring only one tank of gas and little exposure to Covid-19. So Shawna and I headed toward Emporia, KS at late afternoon for our first storm chase of 2020.<br />
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To our surprise, we ended up seeing several tornadoes in open country northwest of Emporia (see images above). Because some didn't seem to get reported, this blog post will document what we saw, and I'll also discuss the setting for Kansas' first tornadoes of 2020.<br />
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After watching two marginal supercells dissipate near Emporia around 6:00 pm CDT, we nearly turned around and headed back to Kansas City. But model forecasts from the morning (more about that later) had consistently indicated that wind shear over eastern KS would pick up at early evening, so we re-focused on a new cell west of Emporia, approaching it heading west from Osage City around 6:30 pm CDT:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFFrL3UIlq3GnYzqQYXXT4jrCpJ1V7G7BSjPVPltXR8UUPpsl3JK1JkkS1dlx4R-XBBIzRrelBqiOi5IlT5R04_c2wu6iyA71m-7lI7qu6UVPCOrj0S3f1PHpjwidAFnZHuAraowR3icuA/s1600/Img_2548_sml_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="720" data-original-width="540" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFFrL3UIlq3GnYzqQYXXT4jrCpJ1V7G7BSjPVPltXR8UUPpsl3JK1JkkS1dlx4R-XBBIzRrelBqiOi5IlT5R04_c2wu6iyA71m-7lI7qu6UVPCOrj0S3f1PHpjwidAFnZHuAraowR3icuA/s640/Img_2548_sml_anno.jpg" width="480" /></a></div>
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Notice the inflow cloud streak pointing into the storm at lower left in the photo above. That often means a storm is beginning to really organize and become a supercell.<br />
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We found a hill a couple miles west of the KS turnpike east of Admire, and watched as the storm base to our west lowered and took on some structure just before 8:00 pm CDT:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhwZ2zhwQfFM4suYSmmxwOovC9zWfQ7DXjC9JbMU6SXRotpVyXR6gb4C7OBq4-yp_LPw8wnKjKtUQMy4ENCNIEkCi9jaql0_19Ja5AUSqxcTKBoA5ua4MwFPb22ecTThsP8PSGSypupZHCl/s1600/snap03_adj_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="469" data-original-width="836" height="356" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhwZ2zhwQfFM4suYSmmxwOovC9zWfQ7DXjC9JbMU6SXRotpVyXR6gb4C7OBq4-yp_LPw8wnKjKtUQMy4ENCNIEkCi9jaql0_19Ja5AUSqxcTKBoA5ua4MwFPb22ecTThsP8PSGSypupZHCl/s640/snap03_adj_anno.jpg" width="640" /></a></div>
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Around 8:05 pm CDT, some scud developed just under the lowering, and Shawna said, "I think that's about to drop a tornado." A moment later, several miles to our west-northwest, it did:<br />
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This tornado north of Bushong lasted a couple minutes.<br />
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Here's a wide view of the Topeka NWS radar lowest-elevation base reflectivity at the time of the tornado, with the meso location and our viewing location indicated (click on images for a larger view):<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhspDARuWXqkhCS4HeT9hPyij_fLXYHRR0MygBMQkdOJbwMKibFQZ3u8xwWmMyZ2UuZbAOUTTt5ZlpaPIhwmuOG9EFSon9tQrOub2fLQiNdG5lwj5g5C2B3FhlcKhX0MlyvS5RKDr5z5m6z/s1600/051520rd0106twx_zoom_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="628" data-original-width="606" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhspDARuWXqkhCS4HeT9hPyij_fLXYHRR0MygBMQkdOJbwMKibFQZ3u8xwWmMyZ2UuZbAOUTTt5ZlpaPIhwmuOG9EFSon9tQrOub2fLQiNdG5lwj5g5C2B3FhlcKhX0MlyvS5RKDr5z5m6z/s400/051520rd0106twx_zoom_anno.jpg" width="385" /></a></div>
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A few minutes later, another "needle" funnel (possibly a tornado) developed from the same mesocyclone as it moved slowly northeast:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg7sga8i5hTaHiWg_mZAmbWxgQOc_SP_9OtbB3jnIG9SbiTaLTb_076bGHVWbUG1kSuVtYMquHpsJCZ-J1KGiEMC3ck-KU8YXoLnUzZnVTQ3keCqlwtI8aNAt9mPVEgmiW3vI0002gc-oj-/s1600/snap17adj_enhcon_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="466" data-original-width="837" height="356" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg7sga8i5hTaHiWg_mZAmbWxgQOc_SP_9OtbB3jnIG9SbiTaLTb_076bGHVWbUG1kSuVtYMquHpsJCZ-J1KGiEMC3ck-KU8YXoLnUzZnVTQ3keCqlwtI8aNAt9mPVEgmiW3vI0002gc-oj-/s640/snap17adj_enhcon_anno.jpg" width="640" /></a></div>
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In the image above, notice the 2nd rain-free base farther west, lower to the horizon. We soon became aware that this was a separate storm some distance to our northwest, and around 8:19 pm CDT, some dust appeared to rise below this base, along with a small "nub" that formed to the right:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg7SDmk5eO1h3DwVt_lSdNyeL6H5a4-pQZYUfWnzQ6v-OxfqeIluAMB7gbYLh-Ltj5deXxbReY8NKF2FlcoHaZKBiBV3UCLC910fhdhNvd0vVboa1pjnch0EIpJz9YeQW7KhNMC2UKWmESB/s1600/snap24_adj_enhcon_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="467" data-original-width="836" height="355" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg7SDmk5eO1h3DwVt_lSdNyeL6H5a4-pQZYUfWnzQ6v-OxfqeIluAMB7gbYLh-Ltj5deXxbReY8NKF2FlcoHaZKBiBV3UCLC910fhdhNvd0vVboa1pjnch0EIpJz9YeQW7KhNMC2UKWmESB/s640/snap24_adj_enhcon_anno.jpg" width="640" /></a></div>
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Here's the radar lowest-elevation base reflectivity view at this time:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiTb_4airS_CS69PFi4SmeeTlYLz_9eIw4Kfmfqlg3rAyw-PiQs0trKQ2-Q4zi8uwt3wmRHugnea0UvDiSAOnwVIsdlgEvO85WmgQzYD6JCQwM30EsfV7QGv1PjmVg25xsI7Umb3XsajbGI/s1600/051520rd0119twx_zoom_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="628" data-original-width="607" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiTb_4airS_CS69PFi4SmeeTlYLz_9eIw4Kfmfqlg3rAyw-PiQs0trKQ2-Q4zi8uwt3wmRHugnea0UvDiSAOnwVIsdlgEvO85WmgQzYD6JCQwM30EsfV7QGv1PjmVg25xsI7Umb3XsajbGI/s400/051520rd0119twx_zoom_anno.jpg" width="386" /></a></div>
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This storm near Alta Vista, KS was 20+ miles to our northwest, but it began to capture our attention while the previously tornadic storm closer to us began to look less organized and moved away. Rather than driving closer through rugged Flint Hills and risk losing visibility behind hills, we decided to stay on the same hill and observe the storm's evolution by zooming in with the video camera.<radar0119></radar0119><br />
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We soon saw rain bands develop along the distant base, and at 8:20 pm a thin funnel extended nearly all the way to the ground. Here's the funnel/tornado at full zoom backlit by lightning, located somewhere southeast of Alta Vista:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhbolfxObIr-y-1zy7TaPS-nkTF7un05C6l5lhzMH1x1cDZ9t_9BrAxNbeB1a2TorMTvfqg6Ez696xyz3Y4DkYmyB1xu_V2fs0NiYAIo-eaan5dAgWn1R9Cn5LRgTxstDzD6fEeKzMRzRvt/s1600/snap26_adj_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="467" data-original-width="838" height="356" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhbolfxObIr-y-1zy7TaPS-nkTF7un05C6l5lhzMH1x1cDZ9t_9BrAxNbeB1a2TorMTvfqg6Ez696xyz3Y4DkYmyB1xu_V2fs0NiYAIo-eaan5dAgWn1R9Cn5LRgTxstDzD6fEeKzMRzRvt/s640/snap26_adj_anno.jpg" width="640" /></a></div>
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This lasted a minute or two while a lowering farther right became visible (see right edge of the image above). <br />
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After the thin funnel dissipated, I zoomed back out to shoot lightning for a couple minutes, but at 8:27 pm CDT I suddenly became aware of what looked like a "cone" tornado on the horizon where the new lowering had been. Here are grainy zoomed-in video images of that feature (apparently a tornado) both in regular contrast at dusk, and also with contrast strongly enhanced:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi-QnVeOzTOgll92FsdsDp5rRwnTv85LP2Dg-e5w9oda-oBqxNRxckw391i3btAWZqwcr0SCtW6ewrZo32mrkcnUgaqvFHS31eUQly2RPwAta3_XGSg3eo1f_N0pYSJRJMXcbtRknmdOXmo/s1600/snap35_adj_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="467" data-original-width="837" height="356" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi-QnVeOzTOgll92FsdsDp5rRwnTv85LP2Dg-e5w9oda-oBqxNRxckw391i3btAWZqwcr0SCtW6ewrZo32mrkcnUgaqvFHS31eUQly2RPwAta3_XGSg3eo1f_N0pYSJRJMXcbtRknmdOXmo/s640/snap35_adj_anno.jpg" width="640" /></a></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgb8O3qT8bFmzApPlmPMvkxSsT0-bcZWImzR-PYTFeXK_DTunjVJ7iJz4_qIVc8I-a8_2h44sJYy4Mvz9kuJECek1xsGTo3QHSrfk5GLlwrrU1iU3TUVLUjAMCXjeUFouYRTVb-GAhJeinN/s1600/snap35_adj_enhcon_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="467" data-original-width="837" height="356" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgb8O3qT8bFmzApPlmPMvkxSsT0-bcZWImzR-PYTFeXK_DTunjVJ7iJz4_qIVc8I-a8_2h44sJYy4Mvz9kuJECek1xsGTo3QHSrfk5GLlwrrU1iU3TUVLUjAMCXjeUFouYRTVb-GAhJeinN/s640/snap35_adj_enhcon_anno.jpg" width="640" /></a></div>
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This feature lasted several minutes before a curtain of rain (the "hook"?) wrapped around from the left and hid it from view. Here's a radar lowest-elevation reflectivity view at about the same time:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgVnPrauDcNQo0KLyOkeH5-wdkl_5RafdWsD9nCPyf7uitAcm3FevyUfhT3Yh2VH3weiGbtL0eHdSG3bwDRboKBEvLkJ5C7xAX3sppKH4wkYygxNouISR38d55xlDYTOw56gLMh9uMFbIHz/s1600/051520rd0130twx_zoom_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="628" data-original-width="603" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgVnPrauDcNQo0KLyOkeH5-wdkl_5RafdWsD9nCPyf7uitAcm3FevyUfhT3Yh2VH3weiGbtL0eHdSG3bwDRboKBEvLkJ5C7xAX3sppKH4wkYygxNouISR38d55xlDYTOw56gLMh9uMFbIHz/s400/051520rd0130twx_zoom_anno.jpg" width="383" /></a></div>
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This sizable-looking "tornado" was located in southwest Wabaunsee County somewhere east-southeast of Alta Vista and west-southwest of Eskridge, KS. I haven't seen any images of it from other chasers. But it sure looked like a tornado, and was co-located with a mesocyclone circulation (marked with black circle on the image above) from radar velocity images (not shown).<br /><br />
After that, we watched lightning for a few minutes, then decided to retreat eastward as two other cells approached from the southwest at dark. With my aging eyesight, I tend to avoid chasing after dark, so we headed back toward Kansas City.<br />
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One of these new cells from the southwest produced yet another tornado, observed by Reed Timmer around 8:45 - 8:55 pm CDT near Council Grove, KS.<br />
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Looking back at the May 14th setting, it wasn't particularly impressive for supercell tornadoes. The morning NAM model 500 mb forecast for that evening showed a weak shortwave trough (red dashed line) approaching Kansas in west to east midlevel flow aloft, but only 20-25 kts of wind over east-central KS, not exactly great support for supercells:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgzMSUuBVmLZ12XUtqnGWX5zXshAxAia7heiG66FqeQrtAoZXv0Jy9_s2mDgHB8YkbY5eeuLEHM75Vtfi0yylek6J6W0DEse1YtVBaycO2pRmaJ6-I0biHWMXJmmCWhDGR4KqBOY0BGnsRv/s1600/051520nam500mb00f12_pvt_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="761" data-original-width="996" height="488" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgzMSUuBVmLZ12XUtqnGWX5zXshAxAia7heiG66FqeQrtAoZXv0Jy9_s2mDgHB8YkbY5eeuLEHM75Vtfi0yylek6J6W0DEse1YtVBaycO2pRmaJ6-I0biHWMXJmmCWhDGR4KqBOY0BGnsRv/s640/051520nam500mb00f12_pvt_anno.jpg" width="640" /></a></div>
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Yet the new HRRR version 4 model (HRRRv4) on the College of DuPage site (with a new panel showing 0-3 km CAPE) showed a decent overlap between low-level CAPE and low-level wind shear (storm-relative helicity or SRH) from the morning forecast valid at early evening:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgXsYE0_I9QHvcG5unkOesfzVPzVtmUS6ucJY2jCLuCGiGn-ADQJ06Z2Tzzz_XWtDqOW3PJW8yzB__SuDVhQ0mPkgDF01O6XQJQUGjGB2mucifdyqyE9QDX_bpvxzZWJDrV95vL5YyiZGHg/s1600/051520hrrv4cp3-srh1-rdr01f13_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="572" data-original-width="1185" height="308" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgXsYE0_I9QHvcG5unkOesfzVPzVtmUS6ucJY2jCLuCGiGn-ADQJ06Z2Tzzz_XWtDqOW3PJW8yzB__SuDVhQ0mPkgDF01O6XQJQUGjGB2mucifdyqyE9QDX_bpvxzZWJDrV95vL5YyiZGHg/s640/051520hrrv4cp3-srh1-rdr01f13_anno.jpg" width="640" /></a></div>
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The same model forecasted a storm that looked like a supercell in the Emporia-Topeka area at the same time (see right-most panel in image above). So, this low-level CAPE/shear overlap suggested a chance of supercell tornadoes via enhanced tilting and stretching of horizontal vorticity within storm updrafts developing in this low-level CAPE/SRH environment, _if_ there would be enough midlevel wind flow and deep-layer shear to support decent supercell storms.<br />
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Moving ahead to the evening, here's the NWS-analyzed surface map at 7:00 pm CDT, with a black oval highlighting the area where storms were developing in east-central KS near and just south of a stationary front:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjMrM8LlKFFRq24Dy-pK_SYGa9rHvqgbaF3ZPbgvQ_nB_kSjCflj1eG50Wx6Aasgyc_1v-BRGftQM4x-vJOEHXbfnAHbjjJZSIzmf1KZwmFJLZ3DpgMzo1m9X00o7DhCyELT2_8YeWGcRAd/s1600/051520sfc00z_us_anno.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="753" data-original-width="969" height="310" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjMrM8LlKFFRq24Dy-pK_SYGa9rHvqgbaF3ZPbgvQ_nB_kSjCflj1eG50Wx6Aasgyc_1v-BRGftQM4x-vJOEHXbfnAHbjjJZSIzmf1KZwmFJLZ3DpgMzo1m9X00o7DhCyELT2_8YeWGcRAd/s400/051520sfc00z_us_anno.jpg" width="400" /></a></div>
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With surface winds from the morning forecasts expected to become more southeasterly at evening over east-central KS, low-level shear would likely increase, along with the deep-layer shear important for supporting supercell storms. That was indeed the case, as seen in this graphic from the SPC mesoanalysis comparing surface to 6 km wind shear at 5:00 pm CDT (left panel) and at 8:00 pm CDT (right panel):<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg_Hwza_7dXJ3B0Z1ajnA4sx9Z8UaOMuMawmGq8mpICf3-Be3PAuoPcw3kAxHl_hfbgw72di55K-uKQ10zoTAgnJSCdRZA4nysvaZaVrBxaWzTXkz7ka2jYxZJ0xG25XwzPdFUsZBRwSsrx/s1600/051520spc06s22-01z_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="573" data-original-width="897" height="408" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg_Hwza_7dXJ3B0Z1ajnA4sx9Z8UaOMuMawmGq8mpICf3-Be3PAuoPcw3kAxHl_hfbgw72di55K-uKQ10zoTAgnJSCdRZA4nysvaZaVrBxaWzTXkz7ka2jYxZJ0xG25XwzPdFUsZBRwSsrx/s640/051520spc06s22-01z_anno.jpg" width="640" /></a></div>
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Notice how the deep-layer shear increased to greater than 30 kt from afternoon to evening, enough to help organize storms into persistent supercells in the Emporia-Topeka area.<br />
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The SPC mesoanalysis at 8:00 pm CDT also showed low-level CAPE and low-level wind shear (SRH) overlapping nicely in the Emporia-Topeka area as south-southeast low-level winds picked up near dark:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh2bfmek9AworM-dNYj2PJrMokc2VE3o2HMmOI3gbqzZqWSB9OlGiX7v9Y8mT8Uv9VBjUd8x4J7XVfkXqL_9OAtq-NeFjezSr4DGWdgqsT8zS0pNSU0xz5C_7Tf5vhkmE89xaIcDcdKMzpW/s1600/051520spccp3-srh101_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="573" data-original-width="905" height="404" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh2bfmek9AworM-dNYj2PJrMokc2VE3o2HMmOI3gbqzZqWSB9OlGiX7v9Y8mT8Uv9VBjUd8x4J7XVfkXqL_9OAtq-NeFjezSr4DGWdgqsT8zS0pNSU0xz5C_7Tf5vhkmE89xaIcDcdKMzpW/s640/051520spccp3-srh101_anno.jpg" width="640" /></a></div>
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This confirmed the HRRRv4 forecast from the morning model run (shown earlier). I've discussed overlapping low-level CAPE and SRH areas in other 2020 case blog posts, and it seems there is increasing evidence that these two parameters _<i><b>together_</b></i> can be useful in assessing environments with supercell tornado potential when deep-layer shear is also supportive.<br />
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Thankfully, Thursday's tornadoes hit in open country, and lasted only a few minutes each. So there was no damage reported.<br />
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As storms organized in the increasing wind shear at dark, thunder became constant and lightning prolific as we watched the supercells to our west and north:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj770sqvUWazLPjGoT5iKj2-rppJS8YUKL3q_gYUdYhAPg6EM4rJNozfgqHgA7Bgv4ZGCfkMiI3khKxpmUBamPJZdtEwzuP8DipGxA8phf6TjJ-74hwmCE2OKnlzINHR4lrqxxWPDu0-PtF/s1600/snap22_adj_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="469" data-original-width="837" height="358" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj770sqvUWazLPjGoT5iKj2-rppJS8YUKL3q_gYUdYhAPg6EM4rJNozfgqHgA7Bgv4ZGCfkMiI3khKxpmUBamPJZdtEwzuP8DipGxA8phf6TjJ-74hwmCE2OKnlzINHR4lrqxxWPDu0-PtF/s640/snap22_adj_anno.jpg" width="640" /></a></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjhT6FtOiSfgBhyphenhyphenStp5oRzuR4PuqDkITfkshzaD6GZHAXdMDJvtk-eN1jSwHA_IqEHHz4NTwHZyLjN0IhlVf4sBgU-ehF_3gOS9HKgsLd2UQ1BWnDcUOF9-GRnVtPN1ZmEoE5VLU4MdcGbK/s1600/snap23_adj_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="470" data-original-width="837" height="358" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjhT6FtOiSfgBhyphenhyphenStp5oRzuR4PuqDkITfkshzaD6GZHAXdMDJvtk-eN1jSwHA_IqEHHz4NTwHZyLjN0IhlVf4sBgU-ehF_3gOS9HKgsLd2UQ1BWnDcUOF9-GRnVtPN1ZmEoE5VLU4MdcGbK/s640/snap23_adj_anno.jpg" width="640" /></a></div>
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Here's an image Shawna took looking south at the edge of the anvil from our cluster of storms, with mammatus visible and mostly clear skies to our south beneath the "cap" at dusk:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhzFCjz1LDjk1_pnRCdvj78XQNCd0nptTxwNGyIOrXgDMBBo4mAN0x2Vf3635HjqBAHJ_jRYByWIG9iQBCE3GlvUnj9Sw-i6RFzb-20MjKcRQFwHmCHWJNTjVz0TMLPAKvdkhHxQ7zK6FpY/s1600/Img_2567_sml_anno.jpg" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="576" data-original-width="768" height="480" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhzFCjz1LDjk1_pnRCdvj78XQNCd0nptTxwNGyIOrXgDMBBo4mAN0x2Vf3635HjqBAHJ_jRYByWIG9iQBCE3GlvUnj9Sw-i6RFzb-20MjKcRQFwHmCHWJNTjVz0TMLPAKvdkhHxQ7zK6FpY/s640/Img_2567_sml_anno.jpg" width="640" /></a></div>
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You just don't see or experience the wide-openness of the Plains living in Kansas City, so it was invigorating to watch storms in open Flint Hills country on May 14!<br />
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- Jon Davies 5/17/20Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com3tag:blogger.com,1999:blog-2399626414603781513.post-70862072940203204752020-04-23T08:02:00.003-07:002020-04-25T08:41:42.716-07:00April 22, 2020 tornadoes in southern Oklahoma - A "high-end" cold-core event?<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg6moDpbXQGLRIRUPA1FdWE1n4t5oimu2XesUYih_J2Xdy7dWWEohZAgD_8NxgDAykT1LTsIDumD8II-hNIaBbnQnxL5V21-0CCgj5MRwTiJCfjMOiLTyHIfZ4Sn-yJr8zZz43OqNDyLFNq/s1600/042220scOKtor_mf1_anno.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="407" data-original-width="543" height="298" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg6moDpbXQGLRIRUPA1FdWE1n4t5oimu2XesUYih_J2Xdy7dWWEohZAgD_8NxgDAykT1LTsIDumD8II-hNIaBbnQnxL5V21-0CCgj5MRwTiJCfjMOiLTyHIfZ4Sn-yJr8zZz43OqNDyLFNq/s400/042220scOKtor_mf1_anno.jpg" width="400" /></a></div>
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*****<i><b> Update 4/24/20: The strongest-rated of the southern Oklahoma tornadoes so far was the one that hit Madill (2nd image above), killing two people (there was some confusion in online reporting the day after the tornadoes, with many news outlets reporting only one death). Also, the strongest-rated tornado of the day was the one that struck Onalaska in southeast Texas, killing 3 people. This massive tornadic supercell moved on across central Louisiana during the evening, killing one other person south of Alexandria as it went on to produce several tornadoes. There were 6 total tornado deaths on April 22, 2020.</b></i> ***** <br />
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Yesterday's tornadic supercells in southern Oklahoma (OK) were photogenic, from the photos above, and also deadly. The tornado in the 2nd image above (by Lane Chapman) killed one person when it hit the south side of Madill, OK shortly before 5:00 pm CDT.<br />
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The top photo above is a large tornado that hit in open country northeast of Ardmore and Springer, in south-central OK, and the 3rd image above is a tornado near Wapanucka, OK, west of Atoka in southeast OK.<br />
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Much farther southeast, a large tornado struck Onalaska and Seven Oaks in southeast Texas (TX) around 6:00 pm CDT (bottom image above). Sadly, this large "wedge" tornado killed 3 people near Onalaska. It was far removed form the setting in Oklahoma and spawned by a monster supercell that continued through southeast TX and on into central Louisiana during the evening.<br />
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My focus in this discussion will be on the tornadoes in southern OK, where forecasters expected tornado development, and did a great job anticipating this event. But it also was a bit unusual for April in that it involved a "cold-core" low at 500 mb (roughly 18,000 ft MSL) near the OK-Kansas border moving <i><b>east-southeastward</b></i> as a "positive" tilt wave disturbance across Oklahoma and Texas (see NAM 500 mb model forecast for mid-afternoon below, with "spreading" flow indicated ahead of the wave):<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhh0knzrBDEdC0mx10nmUYEvUKpOVE6rBAu4pejUELVLF14Ag4r19uiJyhdJUGV3xfJe3s93FHDVVzCy9Ey6Tdnf0tlR0L0v4UO7hPkCTuhmfLOOf1HTNizNElWlWKlRIicvRiHYF7X24dL/s1600/042220nam500mb21f09_pvt_anno.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="759" data-original-width="997" height="484" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhh0knzrBDEdC0mx10nmUYEvUKpOVE6rBAu4pejUELVLF14Ag4r19uiJyhdJUGV3xfJe3s93FHDVVzCy9Ey6Tdnf0tlR0L0v4UO7hPkCTuhmfLOOf1HTNizNElWlWKlRIicvRiHYF7X24dL/s640/042220nam500mb21f09_pvt_anno.jpg" width="640" /></a></div>
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My experience has been that 500 mb "cold-core" lows (see <a href="https://journals.ametsoc.org/doi/pdf/10.1175/WAF967.1">this paper</a>) moving east-southeast early in the season aren't that effective at producing significant tornadoes, but this system was an exception. This was probably due to the large amounts of total CAPE available (2500-3500 J/kg, not shown) because of surface dewpoints in the upper 60's and low 70's F into southern OK at mid-afternoon (see 4:00 pm CDT / 2100 UTC surface map below):<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg75DGBUriCxDwhcNBXhUgZZGnK2H1Q8hpeB36c6BOcBwdt240YEx5yA_D3JsCbm-EOdpi9pbzvj4CUXIOeCe2NLPuz5_C4AMm7CiGUBXKvO3tAgsiBj0AVTLTz8rlexP9SKv_AxwcQhDOn/s1600/042220sfc2058_anno.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="567" data-original-width="559" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg75DGBUriCxDwhcNBXhUgZZGnK2H1Q8hpeB36c6BOcBwdt240YEx5yA_D3JsCbm-EOdpi9pbzvj4CUXIOeCe2NLPuz5_C4AMm7CiGUBXKvO3tAgsiBj0AVTLTz8rlexP9SKv_AxwcQhDOn/s640/042220sfc2058_anno.jpg" width="627" /></a></div>
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Most early spring cold core events in the Plains involve dewpoints only in the 50's F, usually resulting in comparatively weak tornadoes. But there are "high-end" cold-core events that have much more moisture, such as 7/19/18 in central Iowa and 10/4/13 in northeast Nebraska. With access to larger moisture and CAPE, and these can produce stronger tornadoes. </div>
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Notice how narrow the moisture axis was over south-central OK on the surface map above, southeast of the surface low. This is typical of cold-core tornado events. Also notice how the 500 mb and surface pattern matched this composite "cold-core" pattern below, <b>_<i>if</i>_</b> you rotate the composite pattern clockwise 60-90 degrees:</div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEijDNDVJWLdNZcjRH3nC7F54XfxItV6wGW-MkeoLTkHAOap5yvKbuD1R2rxgKYm1XfEHd4P9tC8gw4tcChVcOLTKwX_P9rZ1oQaAZCRoAjK1yHBm6ftuWg9WyzNroL_IRajgjiZDfQrzvRj/s1600/cold-core_setting-typical.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="574" data-original-width="658" height="348" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEijDNDVJWLdNZcjRH3nC7F54XfxItV6wGW-MkeoLTkHAOap5yvKbuD1R2rxgKYm1XfEHd4P9tC8gw4tcChVcOLTKwX_P9rZ1oQaAZCRoAjK1yHBm6ftuWg9WyzNroL_IRajgjiZDfQrzvRj/s400/cold-core_setting-typical.jpg" width="400" /></a></div>
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In the April 22nd case, the warm front was moving <i>eastward</i> instead of northeastward, due to orientation of the upper flow, and the tornadoes occurred along the warm front just southeast of the surface low.<br />
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Here's a visible satellite image at 4:26 pm CDT showing the "arc" of discrete tornadic supercells in southern OK associated with the cold-core setting, as well as the soon-to-be tornadic supercell in southeast Texas that was <i><b>far-removed from the cold-core pattern farther north</b></i>:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJCcg4BDVBTgIejODDsVWahySjpys2nWEcZuI1_Rin0X_F2D0eyqMW-IP4UQAga0spU68WPmQ_aQ320SlqwvOHG3zxlJcE5Gn5vTVqAelw7ow06x_rniEvLCWE1DUsNrdFlHS_K53Oqn4u/s1600/042220sat2146_anno.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="577" data-original-width="666" height="553" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJCcg4BDVBTgIejODDsVWahySjpys2nWEcZuI1_Rin0X_F2D0eyqMW-IP4UQAga0spU68WPmQ_aQ320SlqwvOHG3zxlJcE5Gn5vTVqAelw7ow06x_rniEvLCWE1DUsNrdFlHS_K53Oqn4u/s640/042220sat2146_anno.jpg" width="640" /></a></div>
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And here is the SPC mesoanalysis depiction of 0-3 km MLCAPE (low-level CAPE) and 0-1 km storm-relative helicity (SRH; low-level wind shear) at 4:00 pm CDT / 2100 UTC, shortly before the tornadoes in southern OK:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj1_LfqAVyM8bAUvIinmqQLsUOsK2jSgr3pHzViYG_VkxS4mjcM7w2HqApTbsIKJRMSVwL3SsYSxRV7X7nc6J7pCi7j50-rdZgtLOa1bvrEWUmnDbOXcbSVrr9l6gdhQW2tfCZawF5DQVkf/s1600/042220spccp3-srh21z_anno.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="649" data-original-width="1047" height="396" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj1_LfqAVyM8bAUvIinmqQLsUOsK2jSgr3pHzViYG_VkxS4mjcM7w2HqApTbsIKJRMSVwL3SsYSxRV7X7nc6J7pCi7j50-rdZgtLOa1bvrEWUmnDbOXcbSVrr9l6gdhQW2tfCZawF5DQVkf/s640/042220spccp3-srh21z_anno.jpg" width="640" /></a></div>
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In the low-level CAPE field, you can see how narrow the moisture axis was over southern OK. Often, narrow axes of moisture work against tornadoes because the storms "outrun" the surface-based moisture before relevant processes can work together to generate tornadoes. But in the case of tornadoes associated with cold-core tornadoes, the low-level CAPE is so large that, if sufficient low-level wind shear or SRH is also present, low-level stretching within storms and rotating updrafts can occur <i><b>rapidly</b></i>, so that the narrow moisture axis is not a problem. The fact that all this is occurring along an advancing warm front probably helps, too, because warm frontal boundaries are often good at generating tornadoes due to increased wind shear and warming/moistening air along them.<br />
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Another clue that the April 22nd case had some "cold-core" factors involved is some of the photos I've seen. This one (by Maddi Frizzell on Twitter) shows the ending phase of the tornado northeast of Springer, OK:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhPKw4nCsAimkBcGHt0q2evp93x1dP5kb4KRnTxchJ_xfiP7ZONaKkRXSearYhpzmBjpoE95vHVY4n6wTkDC0m-YYLMq9ZmhxiEa27hgzljDR1mC-nu2gv-N-3i86bWp6CXgNEelwL7xHwi/s1600/042220scOKtor_mf4_anno.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="601" data-original-width="417" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhPKw4nCsAimkBcGHt0q2evp93x1dP5kb4KRnTxchJ_xfiP7ZONaKkRXSearYhpzmBjpoE95vHVY4n6wTkDC0m-YYLMq9ZmhxiEa27hgzljDR1mC-nu2gv-N-3i86bWp6CXgNEelwL7xHwi/s640/042220scOKtor_mf4_anno.jpg" width="441" /></a></div>
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This image shows the full updraft visible, with the tornado at the very back edge of the storm, so typical of many cold-core tornadic storms. Although the April 22nd supercells in southern OK weren't "mini-supercells" as in so many early spring cold-core events, they weren't especially tall, as this image shows.</div>
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A final note: Another tornado from the same tornadic supercell that killed 3 people near Onalaska, TX also killed one person in Louisiana (LA) south of Alexandria during the evening. Yet another person died in Louisiana after being swept into a drainage ditch filled with rushing water. </div>
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A very interesting case to study, although I'm sad to hear of the deaths in OK, TX, and LA. We'll see in the coming days what intensity ratings the National Weather Service gives the various tornadoes on April 22nd. </div>
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- Jon Davies 4/22/20 </div>
<br />Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com0tag:blogger.com,1999:blog-2399626414603781513.post-45892525713847534592020-04-14T16:35:00.000-07:002020-04-15T19:22:15.607-07:00Easter Sunday tornado outbreak in the South: Big shear & CAPE combinations on April 12-13 2020 !<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEivJUwzRvJFLmmwHri1X5TZ8k_aU2zWuK-hpE2mqEBV7F6WRlmtDUE1cn7aLTBT_eWlOZNX6TcFfBOi39KFgxGwpILUQVqLfAXrHpq53mNwZHisutKSwx7MtQ1i3ptORTc52n9NqobZzadB/s1600/041220sMStor_ar_anno.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="399" data-original-width="693" height="230" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEivJUwzRvJFLmmwHri1X5TZ8k_aU2zWuK-hpE2mqEBV7F6WRlmtDUE1cn7aLTBT_eWlOZNX6TcFfBOi39KFgxGwpILUQVqLfAXrHpq53mNwZHisutKSwx7MtQ1i3ptORTc52n9NqobZzadB/s400/041220sMStor_ar_anno.jpg" width="400" /></a></div>
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh_iU-Dsfh6QT1fcA4DYwGxiaeC8zMF4SxOfmZiWBoWg4_Z6cin-PJY4kV7s6nnBUsCS6gsSLBRx4A4lrSwrXfGaPI9Te08zXGc3bYLhLGxK2v0hZEqdyutNyNRpYx72RIxocBDlldp9D9g/s1600/041220scMStor_cm2_anno.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="460" data-original-width="870" height="211" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh_iU-Dsfh6QT1fcA4DYwGxiaeC8zMF4SxOfmZiWBoWg4_Z6cin-PJY4kV7s6nnBUsCS6gsSLBRx4A4lrSwrXfGaPI9Te08zXGc3bYLhLGxK2v0hZEqdyutNyNRpYx72RIxocBDlldp9D9g/s400/041220scMStor_cm2_anno.jpg" width="400" /></a></div>
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Easter's big outbreak of tornadoes (see the scary photos above in southern Mississippi) caused <b>29</b> deaths due to tornadoes across the southern and southeastern U.S. that I've been able to confirm online <i><b>(updated as of 4/15/20)</b></i>, and several others from falling trees and flooding. Sadly, here's a list of tornado deaths so far by state:<br />
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southern/southeastern Mississippi (MS), p.m.:<span style="white-space: pre;"> 10</span> dead, 2 tornadoes, both EF4 from same supercell<br />
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northwest Georgia (GA), evening<span style="white-space: pre;">: </span>7 dead, EF2 tornado<br />
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southeast Tennessee (TN), late evening: 3 dead, EF3 tornado<br />
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northwest South Carolina (SC), early a.m.:<span style="white-space: pre;"> </span>1 dead, EF3 tornado<br />
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southern South Carolina (SC) pre-dawn:<span style="white-space: pre;"> </span>8 dead, 2 tornadoes from separate supercells, both EF3<br />
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The outbreak started on Easter at mid to late morning in northern Louisiana (LA), including an EF3 tornado that struck Monroe LA. It progressed through MS during the afternoon, and tornadoes then developed into Alabama and northern Georgia during the evening, and across South Carolina in the early morning hours before dawn. Many tornadic supercells were embedded within lines, and the number of warnings (> 140 within a 24-hour period) came close to the April 27, 2011 super-outbreak. But thankfully, there weren't as many tornadoes and deaths as with that historic outbreak, nor were most of the tornadoes as strong. Yet 29 deaths from tornadoes is unfortunate.<br />
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Another characteristic in common with the April 27,2011 outbreak was the degree of low-level wind shear and instability, which were quite large over a big area. Going back to my work with Bob Johns in the 1990's, here are low-level shear (SRH, or storm-relative helicity) and instability (CAPE) combinations on Easter Sunday (red dots) from RAP model soundings representative of areas where tornado deaths occurred. I've plotted these on top of a scatterdiagram from our study of 1980's tornadoes that was used to develop the energy-helicity index (EHI), still used today in forecasting:<br />
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I've also plotted in yellow above from 2011 values of SRH and CAPE representative of the April 27, 2011 super-outbreak, and the Joplin tornado environment the same year. Notice the broad range of SRH and CAPE combinations, some almost getting up into the range (middle of the diagram) of what was seen during the April 2011 super-outbreak.<br />
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The biggest and strongest tornadoes on Sunday (see tornado pics up at top) were in southern MS deep within the warm sector at mid to late afternoon with two large semi-discrete supercells moving parallel to each other from northeast of McComb MS, to northeast of Laurel MS. Two tornadoes from the southernmost supercell were rated EF4, one near Salem to near Bassfield MS, and another from southeast of Bassfield to areas past Soso and Heidelberg MS (this tornado was 2 miles wide at one point!). These two tornadoes killed 10 people. A 2nd supercell paralleled that supercell to its northwest, producing a very long-track EF3 tornado (path > 90 miles).<br />
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Here's the RAP model 1-hour forecast sounding near Laurel MS while tornadoes from these two supercells were in progress to the northwest and northeast:<br />
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The SRH and CAPE combinations (350+ m2/s2 and 2000 J/kg) were typical of strong or violent long-track tornadoes in the Plains, so it isn't a surprise that two of the tornadoes were violent in intensity.<br />
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At the same time, here's the SPC mesoanalysis depiction of the effective-layer significant tornado parameter (STP) and low-level wind shear (0-1 km SRH):<br />
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As on the RAP sounding above, the STP values were large (> 6.0) over southeast MS, and SRH was also large (300-400 m2/s2), all supportive of strong or violent tornadoes with the supercells indicated.<br />
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Here's a different RAP sounding, this one in northwest Georgia near Dalton during the evening near the warm front where two separate tornadoes killed 10 people total (Murray County GA, EF2, and just east of Chattanooga over the border in TN, EF3) :<br />
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Notice how different this one is compared to the southeast MS sounding! The SRH was huge, > 850 m2/s2 (!), but the CAPE only 700-800 J/kg. This is a reminder of how SRH and CAPE can work together in many different combinations to help generate deadly tornadoes.<br />
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Now a look at the bigger picture... below are 500 mb forecasts (midlevels of the atmosphere) from the NAM model run on Easter morning showing features at 4 pm CDT (1st graphic, click on it to see full size) and 4 am CDT the next early morning (2nd graphic). Inset on both graphics in the upper right hand corner are 0-1 km energy-helicity index (EHI) forecasts from the NAM at the same times (see the scatterdiagram earlier to see how EHI is computed):<br />
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Notice the strong shortwave (thick black dashed line) that was moving through the large longwave<br />
trough over the central U.S., providing strong lift as jet stream winds "spread" (thick white arrows) ahead of it moving east and northeastward across the South. Also notice how much of the southern and southeast U.S. was "overrun" by sizable SRH-CAPE combinations ahead of this shortwave trough, as indicated by the inset EHI forecasts, setting the stage for a potentially deadly tornado outbreak:<br />
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Compare this 500 mb pattern to the one associated with the <a href="http://davieswx.blogspot.com/2020/03/march-3-2020-double-digit-death-toll.html">Nashville tornado in early March</a>, which was a more localized tornado setting. There's quite a difference in breath and orientation of the two different systems!<br />
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It is also interesting to note that tornadoes on Sunday and early Monday occurred largely between the surface warm front (see NWS surface maps below at 6-hour intervals), and the <i>southern</i> "branch" of the fanning jet stream at midlevels (thick white arrow) superimposed from the 500 mb graphics above:<br />
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In a broad sense, this is typical in most outbreaks, with that southern branch of the spreading jet pattern defining the southern extent of tornado activity.<br />
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Most tornadoes on Easter weren't very visible due to supercells embedded in lines, or the tornadoes occurring at night. But here's a photo of a tornado that happened around noon in west-central MS northwest of Yazoo City... this is how the Monroe, LA tornado might have appeared had it been somewhat visible within the rain:<br />
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A few final comments: SPC forecasters did a great job forecasting this outbreak and getting information out to the media several days in advance! That probably saved some lives.<br />
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Also, I have to shake my head a bit at the number of storm chasers traveling long distances to see tornadoes in the middle of a historic coronavirus outbreak. I know travel isolated in a car is probably relatively safe, but contact at convenience stores, gas stations, and hotels seems risky and a little questionable.<br />
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Chaser behavior was also an issue again on Sunday, with video showing two chasers driving the wrong way on one side of an interstate in MS to get around traffic slowed/blocked by debris! And in another video in east-central MS, two chasers appeared to be following a large and difficult-to-see rain-wrapped tornado, driving into what appeared to be the back edge of the tornado circulation where tree tops were bending almost horizontal at road side! That seems too dangerous, and can leave a bad and misleading impression on viewers.<br />
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Anyway, I'm grateful that the death toll on Easter and early Monday wasn't greater, and for the job that forecasters and media did this past weekend. Stay safe and healthy, everyone!<br />
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- Jon Davies 4/14/20 (<i>tornado death counts were updated 4/15/20</i>)Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com2tag:blogger.com,1999:blog-2399626414603781513.post-53622732247283829732020-04-01T06:26:00.001-07:002020-04-01T14:14:54.405-07:00The Jonesboro, Arkansas tornado on March 28, 2020: A subtle and difficult forecast setting.<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhF8OIWfGZ_sH1CkZy8HjYaMIwp8a7qT8dQTWm_0ECJ9hA0_N67jcWnzyl_aUMrIiSpsJn82vgwyO9YzQjFxgRt2wKDVJccdjn_0zIuXaZcjY0JBmBj9Q7a1Sc72rbZUzxSTCGYM9f7AiMO/s1600/032820neARtor_aww_anno.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="310" data-original-width="429" height="288" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhF8OIWfGZ_sH1CkZy8HjYaMIwp8a7qT8dQTWm_0ECJ9hA0_N67jcWnzyl_aUMrIiSpsJn82vgwyO9YzQjFxgRt2wKDVJccdjn_0zIuXaZcjY0JBmBj9Q7a1Sc72rbZUzxSTCGYM9f7AiMO/s400/032820neARtor_aww_anno.jpg" width="400" /></a></div>
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As Covid-19 keeps expanding throughout the U.S. (we all need to keep following social distancing guidelines!), thoughts and well wishes go to people like fellow storm chaser Dr. Bill Hark in Virginia who has been sick with the virus. We hope you recover soon, Bill.<br />
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With this going on and more than 4500 Covid-19 deaths now in the U.S., tornadoes may seem like "small potatoes". But spring is upon us, along with the threat of tornadoes, no fooling intended on this April Fools Day.<br />
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Saturday's EF3 tornado that struck Jonesboro, Arkansas (AR) around 5:00 pm CDT (2200 UTC) is a reminder of that (see photos above). With a tornado watch out a couple hours in advance and good warnings, no one died with 22 injuries reported, which is good news.<br />
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Most meteorologists on March 28 (including me) were focused on the potential for tornadoes over Iowa and Illinois, but the local environment really ramped up quickly in northeast AR during the afternoon, and was more subtle than one might expect prior to a large tornado. So, I spent some time taking a closer look at this event.<br />
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Morning model forecasts did not suggest much low-level shear over AR compared to farther north near a warm front (see 0-1 storm-relative helicity / SRH forecast for mid-afternoon below):<br />
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But as the southern end of a large upper system approached (not shown), a low-level jet at around 5000 ft MSL (not shown) increased from 30 kt to 45 kt over northeast AR during the afternoon, helping to generate enough low-level shear to support tornadoes, which we'll discuss in a bit. What might also be easy to miss is that a subtle boundary also appeared to play a role.<br />
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Below is a 3-panel composite radar image from late evening on March 27 through midday on March 28 showing this northeast-southwest boundary (see white arrows) drifting eastward across Arkansas during the 18 hours before the tornado:<br />
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Although it's not clear what originated this boundary (NWS-analyzed surface maps showed this as a cold front, which I don't think it was), it appeared to stop near Jonesboro and even back up a bit to the west during the afternoon. Here's the surface map I analyzed at 2100 UTC (4:00 pm CDT) about 45 minutes before the tornado struck Jonesboro (notice the backed southeasterly surface wind at Jonesboro). This boundary is shown as a thick red-blue dashed line over AR:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgjoxam4xGZVAuoUpx_VrqvTeJ7ieMRddcUfiXujOQkBavHWMCcGVakvnb7DhL6PuZhaoxhCKu39jUNOMAlQTrnIbfBHTMNGqYEWBVEj8GzZ6P7nnVH73UU5bz8BXc7taMRmB3UgTQjM2wn/s1600/032820sfc2058ia-ar_anno.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="601" data-original-width="419" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgjoxam4xGZVAuoUpx_VrqvTeJ7ieMRddcUfiXujOQkBavHWMCcGVakvnb7DhL6PuZhaoxhCKu39jUNOMAlQTrnIbfBHTMNGqYEWBVEj8GzZ6P7nnVH73UU5bz8BXc7taMRmB3UgTQjM2wn/s640/032820sfc2058ia-ar_anno.jpg" width="443" /></a></div>
And here's a composite radar image at 2125 UTC (4:25 pm CDT) with the boundary from the 4:00 pm CDT surface map above superimposed as a white dashed line:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgQum9bO-rLdr_HT6ff7wQmSoDxHlSsGvrenJZGtuEQT4CSTwj3NOI4A_Fi0XV1vnjuzRfDDp-W7KFocwJ_VZCqdD22_2eR8XP8a9e_TpGSMVq3E4cavA6vaPWYqSre3MxDPvZef7bcMk_8/s1600/032820rdrrrr2125cp_crp_anno.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="407" data-original-width="316" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgQum9bO-rLdr_HT6ff7wQmSoDxHlSsGvrenJZGtuEQT4CSTwj3NOI4A_Fi0XV1vnjuzRfDDp-W7KFocwJ_VZCqdD22_2eR8XP8a9e_TpGSMVq3E4cavA6vaPWYqSre3MxDPvZef7bcMk_8/s400/032820rdrrrr2125cp_crp_anno.jpg" width="310" /></a></div>
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Notice that the Jonesboro tornadic supercell (white arrow, producing its first tornado near Amagon AR at this time, southwest of Jonesboro) appeared to be moving northeast right along this boundary. It's possible this boundary provided increased low-level wind shear and convergence to help support tornadoes.<br />
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Regarding storm environment parameters over northeast AR, the SPC mesoanalysis showed an area of enhanced low-level MLCAPE (0-3 km above ground, 1st panel below) and, although not particularly impressive, an area of somewhat enhanced 0-1 km SRH (around 150 m2/s2, 2nd panel below) near Jonesboro:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj2qoca4sOd-numC3Qx42sEz6zOKSnq27IQeXkMY16hU827byrDe997r9ozyCRmaA8WWZlpGTetIUvnq0CWyPOS9pxM6fKiR-XaEqZxUjgmhjF-XPFHvcWnLHvhK3945sjBb4SOmTod-3r6/s1600/032820spccp3-srh121_anno_2-pnl.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="607" data-original-width="910" height="425" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj2qoca4sOd-numC3Qx42sEz6zOKSnq27IQeXkMY16hU827byrDe997r9ozyCRmaA8WWZlpGTetIUvnq0CWyPOS9pxM6fKiR-XaEqZxUjgmhjF-XPFHvcWnLHvhK3945sjBb4SOmTod-3r6/s640/032820spccp3-srh121_anno_2-pnl.jpg" width="640" /></a></div>
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This "overlap" may have set the stage for enhanced tilting and stretching of low-level SRH with the supercell storm moving along the aforementioned boundary. The 2100 UTC SRH over northeast AR (larger than forecast from the morning model runs) appeared to be the result of the low-level jet increase during the afternoon that I mentioned earlier.<br />
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An additional graphic I put together (1st panel below) shows areas of overlap of 0-3 km MLCAPE > 75 J/kg and 0-1 km SRH > 150 m2/s2 in purple from the 2100 UTC SPC graphics above:<br />
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Notice that the genesis region of the Jonesboro tornadic supercell was in the purple area over northeast AR, again suggesting localized potential for enhanced low-level tilting and stretching of SRH along the boundary discussed above. The 2100 UTC effective-layer significant tornado parameter (STP, 2nd panel above) also suggested support for supercell tornadoes over northeast AR.<br />
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Here's the 1-hour forecast sounding from the RAP model for Jonesboro valid at 5:00 pm CDT (2200 UTC) at the time of the tornado, suggesting the localized support for supercell tornadoes near the boundary:<br />
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Although both STP and the energy-helicity index (EHI) weren't especially impressive (both parameters around 2.0) for a large EF3 tornado, they do indicate an environment supportive of tornadoes, one that may have been given a "boost" by the presence of the boundary in addition to the sounding environment shown above.<br />
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Here's a larger view of the forecast afternoon setting from the morning NAM model run, showing the large 500 mb trough moving through the central U.S. with the typical spreading jet stream pattern (thick white curved arrows) ahead of it, providing dynamic forcing and lift:<br />
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The insets on the graphic above show EHI and fixed-layer STP forecasts for mid-afternoon (again, not very impressive for northeast AR compared to areas farther north), and SPC tornado reports during the afternoon.<br />
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This case is a good illustration of how important it is to monitor features and parameters in real time, as the mid-afternoon SPC mesoanalysis and surface map indicated increasing low-level shear and support for supercell tornadoes near the boundary over AR, which was not forecast well by the morning model runs. <br />
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Away from Arkansas, notice that over Iowa this was a <a href="https://journals.ametsoc.org/doi/pdf/10.1175/WAF967.1">"cold-core" tornado event</a> with a closed 500 mb low nearby and a boundary intersection (warm front and Pacific cold front) over central Iowa (see the surface map earlier above). As is typical with cold-core settings, several tornadoes occurred near this boundary intersection over Iowa as it evolved northeastward during the afternoon, including this tornado northeast of Des Moines near Rhodes, Iowa after 4:00 pm CDT:<br />
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Back to Arkansas, the Jonesboro tornado setting and environment was more subtle than those accompanying recent large tornadoes such as the nighttime <a href="http://davieswx.blogspot.com/2020/03/march-3-2020-double-digit-death-toll.html">Nashville tornado</a> back on March 3 and yesterday morning's tornado near Eufaula, Alabama (March 31). In both those cases, the tornadic supercells were near a warm front or stationary front, and low-level shear was larger and more evident (0-1 km SRH 300-450 m2/s2) than near Jonesboro on March 28 (0-1 km SRH 150-190 m2/s2).<br />
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I hope everyone reading this navigates the Covid-19 outbreak carefully and in reasonable health over the next couple months!<br />
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- Jon Davies 4/1/20Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com0tag:blogger.com,1999:blog-2399626414603781513.post-39279391551176718172020-03-03T14:01:00.000-08:002020-03-05T14:29:34.373-08:00March 3, 2020: Double-digit death toll from nighttime tornadoes in Tennessee <div class="separator" style="clear: both; text-align: center;">
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The first truly major tornado episode of 2020 took place last night in Tennessee where at least 24 people were killed by a tornadic supercell moving straight east through central Tennessee. A large tornado moved through Nashville near the downtown (see above) after midnight, killing 5 people in Nashville and the area east of the city.<br />
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The most deaths (at least 18) occurred in and near Cookeville, 60-70 miles east of downtown Nashville, with a tornado from the same supercell.<br />
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The upper air setting associated with this tornado episode was a little unusual for March. Most such events occur with a large midlevel (500 mb) trough moving east through the southern states of the U.S. and prominent southwest flow aloft over the Tennessee area. But in this case, midlevel flow was west to east over Tennessee (see the 18-hour NAM model forecast below), with a positive tilt trough (thick dashed red line) approaching from the west-northwest (rather than the southwest) within a northern branch of the jet stream:<br />
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Another midlevel trough and closed low were way back to the west in northwest Mexico within a separate southern branch of the jet stream. But the flow between these two jet stream branches was "spreading out" over the Tennessee area (see large white arrows in the graphic above), providing strong lift within an area where significant combinations of instability and low-level shear as indicated by the energy-helicity index (EHI) were located (see inset and the yellow oval shown above).<br />
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At midnight CST (0600 UTC, about 35 minutes before the tornado hit Nashville), the effective- layer significant tornado parameter (STP) from the SPC mesoanalysis was sizable (around 3.0) over central Tennesssee, indicating combinations of instability and wind shear that were favorable to support supercell tornadoes:<br />
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At around the same time, the surface map showed a warm frontal segment moving east through central Tennessee, just ahead of the favorable STP environment shown above:<br />
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Areas near warm fronts where instability and wind shear are increasing (as indicated by the earlier STP graphic) are good tornado producers when the warm, moist air moves north and east, and this case was no exception.<br />
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The High-Resolution Rapid Refresh (HRRR) model forecast from mid-morning on March 2nd did a reasonable job suggesting the tornado potential for the coming nighttime hours going into March 3rd. The model forecast supercell storms over western into central Tennessee (note the black rotation tracks on the radar forecast below), along with forecast 6-hour updraft helicity swaths from 0200 UTC to 0800 UTC (also below) suggested storm rotation and certainly possible tornadoes given the instability and shear environment discussed earlier.<br />
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Just prior to the tornado in Nashville, the RAP model analysis sounding at 0600 UTC showed a setting with large low-level and deep-layer shear (0-1 km SRH > 400 m2/s2, and 0-6 km shear > 60 kt) and adequate instability (MLCAPE around 800 J/kg):<br />
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Above, I've highlighted in yellow the most important parameters regarding support for supercell tornadoes. The STP and EHI values, while supportive of tornadoes (around 2.0 to 3.0), weren't unusually impressive for a killer tornado with double-digit deaths, probably due to this being an early season event with large shear but relatively small CAPE, typical of cool season tornadoes in the southeast U.S. But, notice the large amount of low-level CAPE below 3 km (125 J/kg of "3CAPE" at lower left on the graphic above). Put that with the large low-level shear/helicity and deep-layer shear, and that probably facilitated strong low-level tilting and stretching of vorticity within the supercell storm updraft to generate a tornado stronger than one might expect with less than 1000 J/kg.<br />
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Here's another image of the tornado moving near downtown Nashville, as indicated by the power flash left of the skyline:<br />
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As I write this, preliminary survey information suggests at least EF3 intensity with the tornado in areas just east of downtown Nashville. Given that this tornado occurred in a metro area after midnight, it is fortunate that the death toll in Nashville wasn't higher, possibly indicating some effectiveness of warnings there. Sadly, death tolls were larger farther east as the storm tracked toward east-central Tennessee in the middle of the night, a difficult time to make people aware of tornado warnings.<br />
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Jon Davies - 3/3/20<br />
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*********** UPDATE 3/5/20 *************<br />
The tornado that hit Putnam County and Cookeville around 70 miles east of Nashville has been rated EF4 (violent in intensity) with 18 deaths and 88 injuries. Please consider helping the tornado victims in Tennessee... here are a couple sites you can visit regarding donations:<br />
<a href="https://www.cnn.com/2020/03/04/us/how-to-help-nashville-tennessee-storm-victims/index.html">CNN - How to help Tennessee storm victims</a><br />
<a href="https://www.kiro7.com/news/trending/heres-how-help-tennessee-tornado-victims/YOC7JNU2N5DPVBRZGNX6JFMB5I/">KIRO - How to help Tennessee tornado victims</a><br />
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Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com0tag:blogger.com,1999:blog-2399626414603781513.post-46754194792061398572020-01-22T16:58:00.004-08:002020-01-22T17:01:30.870-08:00ChaserCon 2020 is almost here... Tornado Forecasting class on Friday, January 31!<div class="separator" style="clear: both; text-align: center;">
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Hi everyone!<br />
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ChaserCon 2020 is a little over a week away. I'm doing a Tornado Forecasting class on Friday evening January 31 from 7:00 to 9:30 pm, with a break in the middle. You can sign up at:<br />
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<a href="http://chasercon.com/node/18">http://chasercon.com/node/18</a><br />
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It's $30.00 per person... Just scroll down to the bottom of the page at the link above to register for the class.<br />
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I'll do more examples and interactive exercises covering supercell tornadoes than last year at Wichita, including a cold-core tornado case. So don't miss it if you're interested in forecasting.<br />
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There's room for around 100-110 people, and we're up to 83. Sign up soon!<br />
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I'll also be doing a talk on Saturday afternoon (February 1) about the crazy and confusing tornadic HP supercell in northeast Kansas last May 28, as part of the conference.<br />
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This will be the last ChaserCon in Denver hosted by Roger and Caryn Hill, so come if you can. Hope to see you there!<br />
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(Thanks to Bill Hark for the photo at top from my class last year in Wichita.)</div>
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- Jon Davies 1/22/20<br />
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Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com0tag:blogger.com,1999:blog-2399626414603781513.post-69772286232882840382019-12-19T07:20:00.000-08:002019-12-19T08:16:33.662-08:00Southern tornado outbreak leaves 3 dead on December 16, 2019<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJuWCz5AAJo8UW5C9nt6M6N7p_F9LL53xlcVvKf5uu2b5PVVa91cfxTlL1cFkomoFEDliE2Rw760NMRRgDX-hV1VyRYSJc2x-y0Oq0rWrInVQr15TBctfjPO1SN2RknUdISoiefLgLwR1M/s1600/121619cLAtor_thw5_anno.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="327" data-original-width="633" height="206" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJuWCz5AAJo8UW5C9nt6M6N7p_F9LL53xlcVvKf5uu2b5PVVa91cfxTlL1cFkomoFEDliE2Rw760NMRRgDX-hV1VyRYSJc2x-y0Oq0rWrInVQr15TBctfjPO1SN2RknUdISoiefLgLwR1M/s400/121619cLAtor_thw5_anno.jpg" width="400" /></a></div>
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A strong storm system moving across Louisiana (LA), Mississippi (MS), and Alabama (AL) on Monday, December 16, 2019 caused the first tornado deaths in the U.S. since May 2019. A large long-track EF3 tornado above (at top) in west-central and central LA left one person dead near DeRidder, and was on the ground for over 60 miles, striking Alexandria around noon on Monday.<br />
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Another tornado (EF2) at late afternoon from a supercell embedded within a squall line killed a married couple in Lawrence County in northwest AL. The bottom photo above shows an EF2 tornado north of Tupelo MS earlier from the same embedded supercell. In all, around 30 tornadoes were reported in LA, MS, AL, and Georgia on December 16 through December 17.<br />
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The 2-panel base reflectivity radar composite image below shows the deadly tornadic supercell at midday over west-central LA (1st panel), and the deadly tornadic supercell within a bowing line segment at late afternoon over northwest AL (2nd panel). Prolific tornadic supercells over southern MS are also indicated:<br />
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This storm system was a good example of a large "positive" tilt trough in mid-levels (see thick red dashed line on 500 mb forecast graphic from the NAM model below) causing a significant amount of severe weather. As noted on the <a href="https://www.weather.gov/jetstream/basic">NWS "Jet Stream" educational site</a>, positive tilt upper troughs (where the southern end of the trough is much farther west than the northern portion) tend to produce the <i>least</i> amount of severe weather, but that certainly wasn't the case on December 16:<br />
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A broad pattern of spreading jet branches (thick white lines and arrows on graphic above) ahead of this trough was causing upward forcing over the southern states. With plenty of wind shear and enough instability present at midday over LA and MS to support supercell tornadoes (see inset showing energy-helicity index or EHI above, combining instability and low-level shear), the outbreak was in progress from late morning on. Note that the southern jet branch above tended to define the southern end of the severe outbreak area, while the northern extent of instability defined the northern end.<br />
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Here's a U.S. surface map at midday showing the cold front and surface low pressure associated with the midlevel trough moving east across the western Southern states:<br />
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A RAP model sounding at midday at Alexandria LA shows how primed the atmosphere was for tornadoes over this area:<br />
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There was close to 2000 J/kg of MLCAPE, around 250 m2/s2 of 0-1 km storm-relative helicity (SRH), and over 50 kt of deep-layer wind shear. Add to that a lack of convective inhibition (MLCIN) and plenty of CAPE in low levels below 3 km above ground (100-150 J/kg) to promote low-level stretching of updraft parcels, and this was an environment very supportive of supercell tornadoes with discrete or semi-discrete cells.<br />
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In recent years, the introduction and use of updraft helicity in computer model forecasts can help forecasters predict where rotating supercell storms (and, by association, possible tornadoes) may develop and track. A HRRR model forecast from the morning of December 16 (below) suggested that long-track supercells would develop from central LA into southwest MS between 1500 UTC (9 a.m. CST) and 2100 UTC (3 p.m.CST), which was a good model forecast:<br />
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By mid to late afternoon at 2200 UTC (4 p.m. CST), the focus for supercells and tornadoes had shifted east to Mississippi and northwest Alabama, as seen on the SPC mesoanalysis graphic below:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg0PHE3lSbOAkRkfkbmmlBRHep5GnIQ7mEhbegEsJPj2IOsZw7NpxQtVRCk2mvnUaknua0AZ5mVo99p_gZpXokrgwZts9OBpQX6ovyrSHVP5jFZwEUkQxrFdR0RvxTdHC5PWu68J_eOiHNI/s1600/121619spccp3-srh122_anno.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="629" data-original-width="820" height="490" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg0PHE3lSbOAkRkfkbmmlBRHep5GnIQ7mEhbegEsJPj2IOsZw7NpxQtVRCk2mvnUaknua0AZ5mVo99p_gZpXokrgwZts9OBpQX6ovyrSHVP5jFZwEUkQxrFdR0RvxTdHC5PWu68J_eOiHNI/s640/121619spccp3-srh122_anno.jpg" width="640" /></a></div>
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The best combinations of low-level wind shear (0-1 km SRH) and low-level instability (0-3 km MLCAPE, see black oval-enclosed area above) were over Mississippi into northwest Alabama, where low-level stretching and tilting of wind shear within stronger storms would be enhanced, supporting low-level rotation and tornadoes. The cells marked "A", "B", and "C" in the graphic above were consistent long-track tornado producers.<br />
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The supercells marked "B" and "C" on the SPC graphic above were particularly effective tornado producers. From these cells, images in sequence below show a large mid-afternoon tornado northwest of McComb MS, a large tornado shortly before 5 p.m. CST near Columbia MS, and the EF3 tornado that struck Laurel MS at dark. Power flashes are quite visible in the latter two images:<br />
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As is so often the case these days, excellent NWS warnings and media coverage probably saved many lives in this outbreak.<br />
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- Jon Davies 12/19/19Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com0tag:blogger.com,1999:blog-2399626414603781513.post-54914831825161960562019-10-22T22:34:00.000-07:002019-10-24T21:31:39.907-07:00October 20, 2019 Dallas, Texas tornadoes after dark - no deaths or injuries!<div class="separator" style="clear: both; text-align: center;">
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Wow... it has been an active several days for tornadoes this past weekend in October (see my recent post about the <a href="http://davieswx.blogspot.com/2019/10/october-18-2019-strong-florida.html">EF2 tornado in Florida from T.S. Nestor</a>).<br />
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As anyone watching news the last couple days knows, Sunday evening (10/20/19) saw several tornadoes in the Dallas, Texas area after dark, including one EF3 that struck the North Dallas-Richardson corridor around 9 pm CDT (top image above). Another of EF1 intensity hit the Rowlett, Texas area a little later from the same supercell storm (middle and bottom images above, note the very impressive power flash!) .<br />
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****<b> Update 10/24/19: </b> <i>Additional tornadoes have been surveyed by NWS Dallas/Ft. Worth in recent days, including a short-track EF2 tornado in Garland just before the Rowlett tornado mentioned above, and an EF1 in Rockwall after the Rowlett tornado. These tornadoes were from the same supercell that produced the North Dallas and Rowlett tornadoes.</i> ****<br />
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No one wants to see damaging tornadoes in a metro area, especially after dark, but it is great news that there were no injuries or deaths reported in the Dallas area, largely due to a tornado watch and good warnings by NWS.<br />
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I've had several people ask me, "Isn't that odd for this time of year?" Not really. Based on statistics over the past 25 years, Texas sees an average of around 9 tornadoes in October each year, and 58 tornadoes occur on average nationally in October. So it does happen with the right meteorological settings.<br />
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Sunday evening's surface map (below, 7:00 pm CDT) showed a dryline west of Dallas with moist air (dew points upper 60's to near 70 deg F) that had moved back into north Texas on south winds during the day, with the deepest moisture from the Red River southward:<br />
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Tornado parameters from the SPC mesoanalysis at 7:00 and 8:00 pm CDT (below, enhanced energy-helicity index or EEHI, and the effective-layer significant tornado parameter or STP) suggested that combinations of instability and wind shear were quite supportive of tornadoes over the Dallas area as storms were developing rapidly and becoming supercells to the west:<br />
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The northernmost supercell on the 7:00 and 8:00 pm SPC images above produced the damaging EF3 tornado in north Dallas around 9:00 pm CDT, followed by the Rowlett tornado just after 9:30 pm CDT. In fact, the warm sector setting east of the dryline over north Texas was so supportive of tornadoes that no boundaries were needed to help produce tornadoes, unlike last Friday evening in Florida.<br />
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A forecast of instability and wind shear from the RAP model sounding at Dallas a couple hours before the tornado shows excellent combinations of CAPE (instability), low-level wind shear (0-1 km storm-relative helicity or SRH), and deep-layer wind shear (0-6 km shear) were in place, with not much convective inhibition (CIN) in the environment. These factors were all supportive of significant supercell tornadoes if discrete storms developed:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjTVMHs1BxOaqFmRqTD_zKD7ytnPrEQeHJWM8wfAZ0ocON7nBqp1DevZTpn7w4mefrApu-sEIzi1dk-L_CoHnVfOLqrHxwSPsaya8BcA-COZhrm9iVCmDQ152-uG-zyCfZZHb8XPMEnmx6L/s1600/102119dal02rapf02_cod_anno.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="777" data-original-width="1189" height="417" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjTVMHs1BxOaqFmRqTD_zKD7ytnPrEQeHJWM8wfAZ0ocON7nBqp1DevZTpn7w4mefrApu-sEIzi1dk-L_CoHnVfOLqrHxwSPsaya8BcA-COZhrm9iVCmDQ152-uG-zyCfZZHb8XPMEnmx6L/s640/102119dal02rapf02_cod_anno.jpg" width="640" /></a></div>
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It is worth noting that the High-Resolution Rapid Refresh (HRRR) model from earlier on 10/20/19 (see below) was<i> <u>not</u></i> successful in forecasting convective storms and supercells over the Dallas area that evening, although it did forecast storms in Oklahoma, and over west central Texas:<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgJEEfobQKTmqFOxu0EhBu10iIxYAXx4WU9Ai7w2C3qEepbo1YrwRgMe-eS0zLvCyB7iGYOdmgb8HEbRRXx4h32SXrk2XHjNUnxP-Wm4IDjv8emEbA93c69aVVrRk8w1F-fqzt_0dmgzySb/s1600/102119hrrrdr02f11_anno.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" data-original-height="599" data-original-width="783" height="488" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgJEEfobQKTmqFOxu0EhBu10iIxYAXx4WU9Ai7w2C3qEepbo1YrwRgMe-eS0zLvCyB7iGYOdmgb8HEbRRXx4h32SXrk2XHjNUnxP-Wm4IDjv8emEbA93c69aVVrRk8w1F-fqzt_0dmgzySb/s640/102119hrrrdr02f11_anno.jpg" width="640" /></a></div>
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So, even with our often impressive automated model guidance of convective storms these days, the human forecast element is still greatly needed!<br />
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In my post this past weekend about the Lakeland, Florida tornado, I pointed out from radar images how that supercell behaved somewhat like a typical Plains tornadic supercell with one tornadic mesocyclone occluding and dissipating, while a new one formed to its east-southeast. That same evolution was seen Sunday evening with the North Dallas and Rowlett tornadic mesocyclones, as is evident on the reflectivity and storm-relative velocity images below:<br />
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Looking at the larger synoptic picture, the NAM model 500 mb forecast for that evening showed a very large and strong midlevel trough (dashed red line below) moving through the Central Plains, with a typical "branching" jet pattern ahead of the trough. This area of dynamic forcing overspreading the returning low-level moisture through the Plains was where the bulk of severe weather occurred Sunday evening and Sunday night:<br />
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One final note... The north Dallas tornado touched down 15-20 miles east-northeast of AT&T Stadium where the Dallas Cowboys were playing at the time of the tornado. Although the soon-to-be tornadic North Dallas supercell stayed well north of the stadium, it is nevertheless very fortunate that the EF3 tornado did not directly impact the thousands of people at the game!<br />
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- Jon Davies 10/22/19Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com1tag:blogger.com,1999:blog-2399626414603781513.post-70344425675409022482019-10-19T19:39:00.003-07:002019-10-19T19:54:04.556-07:00October 18, 2019: A strong Florida supercell tornado with Tropical Storm Nestor<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhCtdrml45CWy80t975Lt_bD6yuxP30FI4-jSXfJNdGSINT0OqGRCmQvNBOtryFA8GL58MW1guRBy0vKC303pFMplgp8Jk3CCu-Jcd4x5yysjjzwTjgdrM8Uy_R6cHeuE1SDDr0dXz2EvIn/s1600/101819wcFLtor_elm_anno.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="300" data-original-width="361" height="265" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhCtdrml45CWy80t975Lt_bD6yuxP30FI4-jSXfJNdGSINT0OqGRCmQvNBOtryFA8GL58MW1guRBy0vKC303pFMplgp8Jk3CCu-Jcd4x5yysjjzwTjgdrM8Uy_R6cHeuE1SDDr0dXz2EvIn/s320/101819wcFLtor_elm_anno.jpg" width="320" /></a></div>
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It's been awhile since I posted about a recent tornado case, so I pulled together some graphics about the meteorological setting with last evening's EF2 tornado after dark (see images above) near Lakeland in west-central Florida east of Tampa. This tornado was associated with a tropical storm (T.S. Nestor, centered well out in the Gulf of Mexico at the time). But instead of the supercell being embedded within an outer band of storms as with many tropical systems, it was discrete and occurred near an east-west stationary front, behaving in some ways more like a Plains supercell storm.<br />
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The stationary front is shown on the surface map below at about 0300 UTC (11:00 pm EDT), about the time of tornado development near Lakeland:<br />
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There was not a tornado watch in effect at the time, probably because the environment most supportive of significant tornadoes appeared to be out in the Gulf of Mexico closer to the center of Nestor, as indicated on the 0300 UTC (11:00 pm EDT) SPC mesoanalysis graphic below using the effective-layer significant tornado parameter (STP):<br />
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However, low-level wind shear (0-1 km storm-relative helicity or SRH) and low-level CAPE (0-3 km MLCAPE) on the SPC mesoanalysis at 11:00 pm EDT (below) were notably co-located together over west-central Florida near the stationary front:<br />
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This was in the same area where a supercell storm (shown in later graphics down below) was moving north-northeast near and across the stationary front. The combination of these two low-level parameters near the ground probably facilitated low-level stretching and tilting of environmental vorticity into the storm's updraft to produce strong low-level rotation, even though total instability and numerical shear/instbility combinations did not appear especially large. The stationary front likely provided additional low-level shear to add to the background environment as the supercall moved across the front.<br />
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A 3-hr forecast sounding from the RAP model at Lakeland valid at 0300 UTC (11:00 pm EDT) also suggests that the environment was supportive of supercell tornadoes:<br />
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Notice above that the red CAPE area extended only up to around 30,000 ft MSL (300 mb), with the "fattest" area of CAPE located near 10,000 ft MSL (700 mb), rather low in the sounding relative to the ground. This is similar to many "cold-core" <ref> low-topped supercell environments that support tornadoes in the Plains, suggesting significant upward air acceleration in low-levels, resulting in strong vertical stretching of low-level vorticity near the ground, even though total CAPE does not appear unusually large. </ref><br />
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So, the vertical distribution of CAPE near the stationary front was probably important in this case. Also, deep-layer shear (0-6 km shear) near 30 kts on the sounding above, while not overly impressive, was just enough to support supercells and tornadoes.<br />
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This discrete supercell associated with a tropical system also behaved more like a Plains supercell on radar. The Tampa radar reflectivity and storm-relative velocity images zoomed in below show the original tornadic mesocyclone northwest of Lakeland occluding and dissipating (drifting toward the back side of the storm while wrapping in rain-cooled air), while a new mesocyclone formed to its east and southeast, similar to the evolution of many Plains supercells:<br />
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Thankfully, even though the EF2 tornado was on the ground after dark for 9 miles and was nearly a third of a mile wide at times, there were no injuries due to timely warnings from NWS Tampa.<br />
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- Jon Davies 10/19/19<br />
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Jon Davieshttp://www.blogger.com/profile/14044746324804312344noreply@blogger.com2