Jon Davies Severe Weather Notes

First tornado deaths of 2012 in Birmingham AL area on 1/23/12

2012-01-23T12:01:00.000-08:00

A large deadly tornado (at least EF3 intensity) struck the Birmingham AL area early this morning around 4 a.m. CST (1000 UTC, Monday 1/23/12), killing at least 2 people according to media information at early afternoon.

The weather environment was primed for generating significant tornadoes before sunrise on Monday in Alabama. A RUC analysis sounding at 1000 UTC (see above) at Birmingham while the tornado was moving through showed a massively large wind profile (hodograph) with nearly semi-circular curvature, ideal for generating low-level rotation in storms when notable instability is also present. In this case, there was around 700 m2/s2 of storm-relative helicity, with mixed-layer CAPE between 1000 and 1500 J/kg, putting the storm environment in a statistically dangerous area on an SRH-CAPE diagram (see red dot on scatterdiagram above) regarding support for strong or violent tornadoes. Compared to last Saturday's environment with severe storms in central Georgia (1/21/12, not shown) where representative SRH values were around 300 m2/s2 and CAPE was only 300-400 J/kg, this was a much more dangerous and life-threatening setting.

The overnight SPC mesoanalysis also suggested potential for significant tornadoes (see the 0900 UTC SPC graphics above), with large SRH-CAPE combinations indicated in the same area where storms were moving through. A strong negatively-tilted trough at 500 mb (roughly 18,000 ft MSL, see last chart above) prompted the deadly severe weather, pulling deep moisture into Alabama from the Gulf of Mexico, generating strong low and mid-level wind fields, and providing strong lift and forcing.

Given that it was still dark when the Birmingham area tornado moved through, the death toll could have been much larger. It surely helped that the storm potential was well-outlooked by SPC already on Sunday, and NWS warnings in the area were timely.

Jon Davies - 1/23/12

11 Jan 2012 "surprise" tornadoes in North Carolina

2012-01-12T15:27:00.000-08:00

Yesterday's EF2 tornadoes in Rutherford and Burke counties of western North Carolina (see photos above) injured 10-15 people (one critically) and came as a bit of a surprise. This case is a good example of how difficult it is to forecast winter-time tornadoes. Instability (CAPE) is often small (around 500 J/kg or less), but wind shear and low-level storm-relative helicity (SRH) are often large (> 200-300 m2/s2); that makes it hard to assess when CAPE and SRH combinations are truly strong enough to support significant tornadoes. It's just as important to assess the strength and focus of the accompanying synoptic setting and how the CAPE/shear environment fits with that.

Wednesday's system (1/11/12) had been a mid-level cut-off low over Texas the previous day (1/10/12, see NAM 500 mb vorticity charts above), and was being pushed rapidly into the Carolinas by a larger wave at 500 mb digging into the Central Plains. Note that although Wednesday's upper system over the Southeast was no longer a closed low, it was now a tight and dynamic short wave with a strong vorticity max moving into the western Carolinas (red area and "X", see arrows), focusing upward forcing. This strong upper wave and vorticity max had also caught up to the associated surface front (blue curved line), addiing to the strong dynamic focus in the western Carolinas area. (The previous day, the same upper vorticity max located in Texas had lagged the surface front in Mississippi by some distance.)

The fixed-layer Sig Tor Parameter at 2100z (STP at 4 pm EST, see SPC mesoanalysis chart above) suggested a marginally favorable environment (> 1.0) for tornadoes over NW South Carolina inching into SW North Carolina, just ahead of the strong upper vorticity center seen earlier and the surface front, near the "triple point" where fronts met (see surface inset). These dynamic factors and environment provided enough focus for the south end cell of a broken arc of low-topped storms (see visible satellite image above) to become a damaging tornadic supercell as it moved into North Carolina.

A similar setting the day before over Mississippi, but with somewhat less focus and slightly less favorable STP values (not shown), did not generate any tornadoes, illustrating how subtle and difficult winter tornado settings with small CAPE can be to assess, in contrast to days like the Joplin tornado where CAPE exceeded 4000 J/kg. Again, an awareness of how synoptic features come together or focus into a particular area (e.g., strong short wave and vorticity max, frontal orientation relative to those features, along with prefrontal environment) is important. Typically, STP or EHI values slightly larger than 1.0 aren't impressive, but the surface and upper-air dynamic focus in this case suggested more attention.

A 2200 UTC RUC-estimated sounding at Shelby NC, about 20 minutes before the first tornado, is shown in the last graphic above. Notice that the CAPE was small (< 500 J/kg), but the SRH moderate to strong (260 m2/s2). With all the CAPE "compressed" below 400 mb (approximately 24,000 ft MSL), rapid supercell updraft accelerations may have been enhanced in low-levels, even though total CAPE was relatively small, helping with tilting and stretching of streamwise vorticity associated with SRH in the environment.

Jon Davies - 1/12/12

The 2011 tornado death toll - 2nd worst in U.S. history!

2011-12-31T13:36:00.000-08:00

Here we are on the last day of 2011, and the U.S. tornado death toll for the year is at least 552, tied with 1936 as the 2nd deadliest U.S. tornado year! (The number of deaths may be even higher depending on how one categorizes them; the city of Joplin lists 161 tornado deaths for the May 22nd tornado instead of the National Weather Service "official" number of 158 deaths, probably due to how NWS categorizes some deaths as "direct" vs "indirect".)

I don't think most people who hear this in passing on TV comprehend how huge this is. In this day and age, that number is incredibly sobering! (See how dramatically 2011 stands out in the chart above among the last 50 years of U.S. tornado deaths.) Many of my colleagues, myself included, thought we would never see such huge death tolls again with the warning systems that are now in place in our country.

Given the violent tornadoes in 2011, without our warning systems, the death toll in 2011 would certainly have been worse. But I also think things could be better. The NWS assessment from Joplin earlier this year concluded there is considerable "desensitization" to warnings in our population from perceived overuse of sirens and warnings.

There obviously aren't easy answers. Some quick random thoughts with the new year upon us:

- Continued and ongoing public education is clearly needed about the importance of severe weather awareness and safety.

- Though not talked about much, siren policies across the country could be more standardized and less confusing... there are big inconsistencies regarding how sirens in different areas are used and activated. For example, some cities such as Joplin run them in shorter 3-minute bursts and then stop (as on the Joplin tornado day) which can be confusing to people in the most dangerous situations (when the sirens stop, is the danger past?), while other cities run them longer. And in many metro areas, sirens tend to be an all or none proposition until technology is installed to activate them only for localized areas directly threatened by an approaching tornado. Siren policies and equipment (as well as the NWS interface with those who activate them) appear to need closer examination and standardization between local governments so we don't inadvertantly train our citizens to ignore them due to a perceived "cry wolf" factor.

- If the NWS endorses use of "tornado emergency" statements to alert populated areas of imminent danger to life, then they can be more consistent in using them. If there was ever a situation that cried out for a tornado emergency statement conveying increased urgency, it was Joplin last May 22nd where 161 people died. But none was issued. By around 5:38 pm when the tornado was entering Joplin (about 20 minutes after a standard-worded "radar-indicated" tornado warning and 3 minute siren burst), there was enough information from radar and spotters to quickly issue a strongly-worded tornado emergency statement for local Joplin media, adding urgency and emphasis in a dangerous life-threatening situation. This would have been timely enough to possibly save some additional lives in spite of the hard-to-see and rapidly-developed violent tornado. The tornado warning was reissued at 5:48 pm with much stronger wording, but why wasn't an urgent tornado emergency statement issued 8 to 10 minutes earlier?

I hope some lessons from last year's tornado disasters (unprecedented for our modern technological age) result in growth and learning for all of us, as well as better tools and preparedness in 2012.

Jon Davies - 12/31/11

Don Harman

2011-11-30T10:33:00.000-08:00

Some extremely sad news today... Long-time Kansas City meteorologist and weathercaster Don Harman died yesterday. He worked at WDAF-TV since 1999, and was very popular on their morning show.

Don had an awesome sense of humor, both on-air and off. He was always enthusiastic about weather, very knowledgeable, and a great communicator. My wife Shawna and I always enjoyed watching him on TV, as well as seeing him at AMS meetings, and have fond memories of the time a few years ago when he interviewed us about our kids book on storm chasing. He was a friend, and we are quite taken aback today at his passing.

With all the posts and discussion Shawna has been monitoring today on Facebook, it is clear that Don was an important part of KC area mornings for many many people, and will be missed beyond words. No one can replace him.

Our hearts and thoughts go out to Don's family and little girl, as well as the staff at WDAF. I can't imagine what they are feeling right now. This is a huge loss...

- Jon Davies 11-30-11

Some further comments about SRH & CAPE in tornado nowcasting

2011-10-03T08:09:00.001-07:00

I've gotten some private responses and discussion about my post last week regarding the Joplin tornado and the use of SRH (storm-relative helicity) and CAPE combinations to assess "more dangerous' tornado enivronments.

Here's excerpts from one response by John Farley, an experienced storm chaser in the western IL/eastern MO area:
"...one problem with what [Jon] is suggesting regarding enhanced warning wording in situations with unusually favorable environments for strong tornadoes might have the unintended effect of contributing to the false alarm problem. I am referring... ...to situations with unusually favorable parameters and tornadic radar signatures, but no "ground truth" confirmation of actual tornadoes at the time the warning is issued... ...On the same day [as Joplin]... ...I was chasing east of Hermann, MO, (west of STL) where the SRH was 300 and the CAPE was 3000. I observed three supercells between around 4 and 7 p.m. that day, two of which were TOR-warned... ...The storm in that area on Jon's 5 p.m. image is the second of the three I observed... I observed strong rotation in this storm, but neither it nor any of the three supercells I observed ever produced a tornado..."

John makes an excellent point. It is a gross-oversimplification to use only the 2 parameters I've discussed so far (SRH and CAPE) for assessing supercell tornado environments. There are most certainly other important ingredients and issues to look at. The situation John has outlined also is a reminder that the decision to use enhanced wording or a "stronger warning" is not simple.

Let's look again at May 22nd, this time at the area where the storms John observed occurred. The 1st graphic above (from my previous post, but with arrows indicating the storm area west of St. Louis) confirms that CAPE and SRH were also large over eastern Missouri at late afternoon on the Joplin day, and would fall well above the red curve on my scatterdiagram (not shown). The 2nd graphic above (also repeated from my previous post) also shows the CAPE and SRH axes on May 22nd from a wider view, as well as EHI (energy-helicity index, combining the two parameters into a single dimensionless number), with the eastern MO storm area indicated by small black arrows. All this information suggests that potentially deadly supercell tornadoes were also possible in eastern Missouri, with large CAPE/SRH/EHI indicated here. But as John noted, tornadoes did not occur, even though storms were rotating.

A closer look at both graphics also shows that the storm area west of St. Louis, unlike the Joplin storm, was on the eastern side of the instability axis moving _away_ from the largest helicity and largest CAPE, and moving _toward_ an area of increasing MLCIN (light blue; SBCIN was even larger near St. Louis, not shown), suggesting some increasing low-level stability as storms moved toward the Mississippi River. Strong tornadoes can certainly occur on the east side of an instability axis, but are almost always near a warm front or within an area of warm advection in low-levels (increasing warmth and moisture) where SRH grows _larger_ as one moves east or northeast into or across the warm advection area. Notice that this was _not_ the case on March 22 in eastern MO, where SRH was trending downward some in value toward the St. Louis area.

To look further at warm advection, the 3rd graphic above is again the Joplin day at 5 pm CDT (22 UTC), while the 4th graphic is 2 days later on 5/24/11 at 5 pm CDT for comparison; both EHI and temperature advection at 850 mb from the SPC mesoanalysis are shown in these 2 graphics, along with surface and radar features. Notice on both graphics, strong warm advection (indicated in pinks and reds) was co-located with the instability/EHI axes where violent tornadoes occurred in southwest MO (the 22nd) and central OK (the 24th), respectively. Also notice that on 5/22/11, the warm advection area was well removed to the southwest from the St. Louis area. In my database work, I've found that the stronger tornadoes are usually associated within or immediately to the south of strong warm advection areas, where lifting and SRH tend to be larger because of the associated atmospheric processes, along with increasing CAPE.

Certainly, the positioning of the storm John was following, on the eastern side of the instability axis and away from the strong warm advection, would not preclude tornadoes from occurring, and a responsible meteorologist should clearly warn on a storm in that environment (as was done) _if_ significant rotation was indicated by radar and/or spotters. But the surface pattern on the 22nd, showing a surface low back in southeast Kansas with increasing SRH and convergence along with enhanced warm advection and energy focus in southwest MO, might suggest that the better potential for strong tornadoes would be there. Adding to this the maximized combinations of SRH and CAPE, southwest MO would be a "red flag" area for possible stronger wording in tornado warnings at late afternoon, while this would appear less true for eastern MO, given the location relative to the instability axis, warm advection, and surface/low-level pattern focus farther southwest.

Again, to be clear in my recent posts, I'm not suggesting that we are able to forecast tornado intensity. And I'm not suggesting that enhanced wording in warnings be used every time SRH and CAPE appear to be in the "more dangerous" part of the scatterdiagram. But I am suggesting that we can detect and see at least some settings where stronger tornadoes are _more likely_. That involves knowledge of surface patterns where winds are backing and the atmosphere is focusing, where warm advection is occurring, thus increasing SRH and CAPE, along with other ingredients. That's a lot different than just looking at points on a diagram; it involves some understanding of important processes in severe weather production and a sense of atmospheric trends and evolution over an area being monitored. On the Joplin day, getting away from the SRH/CAPE points on a scatterdiagram, the atmosphere's _focus_ at late afternoon using surface and other basic weather products appeared rather impressive over southwest MO; look at the strong warm advection east of the surface low in the 3rd graphic above, and the "bulging" EHI pattern back to the northwest east of the surface low. The increasing SRH and CAPE values in this area just "sealed the deal", environment-wise.

Chuck Doswell has written extensively about the danger of using "magic" numbers and indices in weather forecasting. Isolated numbers, indices, and points on diagrams have _no place_ in forecasting without basic knowledge and thoughtful consideration of other issues, such as the surface pattern focus and evolution, along with other ingredients. I apologize if I gave any impression otherwise, when I was oversimplfying using the SRH and CAPE diagram to make a point in limited space. I'll write more about this in future posts.

Thanks, John, for sharing the situation above along with your thoughts and discussion.

- Jon Davies 10-1-11

An additional look at the Joplin tornado, after the assessment report

2011-09-26T11:36:00.000-07:00

The NWS assessment report for the Joplin tornado came out last week (see here and here), 4 months after this horribly tragic event. I was glad to see that the authors of the report picked up on the public perception of high false alarms, and their tendency to ignore warnings and sirens because of an optimistic bias and the perception that "they happen all the time" in southwest Missouri. I was also glad to see some discussion in the report about the possibility of different tiers of warnings, and even different siren tones or patterns to get people's attention in situations that are truly more deadly. These are some things I touched on (particularly a two-tiered warning system) in a discussion I posted at the very tail end of July.

Given the broad environment area of sizable low-level shear and large CAPE present at late afternoon over southwest Missouri on May 22, when significant storm rotation was detected on radar in that environment, particularly moving toward a populated area like Joplin, that would have been a good situation for the use of enhanced wording or even a "higher tier" of warning. And, even though the tornado developed very fast on the southwest edge of Joplin 17 minutes after a tornado warning with standard wording had been issued, it seems possible that if more urgent action had been performed rapidly around 5:40 pm when the first tornado reports were coming in (e.g., a "tornado emergency" statement or reissuing of the tornado warning with more urgent wording prompting continuous sounding of sirens at that point), some additional lives might have been saved.

With the Joplin report now out, this is a good time and context to go back and look at the Joplin setting using SPC mesoanalysis graphics, which are generally good estimates of parameter patterns and ingredients useful in various types of weather forecasting. The first graphic above shows MLCAPE (mean-layer CAPE) and 0-1 km SRH (storm-relative helicity) graphics at 20 UTC (3 pm CDT) on 5/22/11 after the first storm had developed in southeast Kansas near Parsons (black arrow). Notice that while MLCAPE was quite large (> 4000 J/kg), 0-1 km SRH appeared rather unimpressive at this point (around 100 m2/s2). The 2nd graphic above shows the same paramaters, but 2 hours later at 22 UTC (5 pm CDT) about 30 minutes before the Joplin tornado. Notice that MLCAPE was still very large, but 0-1 km SRH had _increased dramatically_ ahead of the supercell complex approaching Joplin (black arrow), more than _doubling in value_ to greater than 250 m2/s2!

Looking at a SRH/CAPE scatterdiagram (3rd graphic above), notice how this low-level shear increase moved the SRH/CAPE data point from below the red curve upward to _well above_ it. This trend was very important, probably helped by a surface low forming over southeast KS (4th graphic). This should have been noted by any mesoscale analyst working as support to radar/warning meteorologists in the southwest MO/northwest AR/northeast OK area that afternoon. Even though no tornadoes had occurred yet in the s.e. KS/s.w. MO area, such an increase would be a red flag for considering the use of enhanced wording in warnings (or a higher tier of warning, if such a system were implemented) based on any significant rotations detected on radar in such an environment, particularly if a very populated area (such as Joplin) were threatened.

Let's contrast the Joplin setting with a situation that occurred at midday in Kansas City on 5/25/11, 3 days later. The last graphic above shows CAPE (11 pm CDT) and SRH (noon CDT), similar to the earlier graphics, though SBCAPE (surface-based CAPE) is used due to the "cold-core" nature (500 mb closed low nearby) of the setting where SB lifted parcels are typically more representative of true instability. Note that SRH was quite meager (around 50 m2/s2), and CAPE was less than 1500 J/kg in the immediate Kansas City area (left black arrows in last graphic above), with the resulting position on the same SRH/CAPE diagram above far to the lower left _well below_ the red curve. Although it is quite possible to get small short-lived tornadoes in such settings, strong "cold core" tornadoes are almost always linked to settings with much larger SRH. Indeed, there were 2 or 3 reports of brief weak tornadoes from south to north across the KC metro area, but certainly no significant damage. Compared to Joplin, the threat over the Kansas City area was small in this situation. But tornado warnings with wording not much different than the intial Joplin warning 3 days earlier prompted several people in KC to call my wife Shawna and me in panic to ask what was going on, given that Joplin had occurred only a few days earlier. We told people to take cover and precautions, but that the risk was only a small fraction of what it had been for Joplin. This is an example of a situation where 2 tiers of warnings (and possibly different siren modes) might be useful in conveying the relative threat to the public.

Admittedly, the Kansas City situation on 5/25/11 was complicated by the rapid increase in parameter values and support for tornadoes some 70 to 80 miles east-southeast of Kansas City, where a significant EF2 tornado hit Sedalia just after noon. With SRH in the 150-200 m2/s2 range and SBCAPE near 2500 J/kg in the Sedalia area and southeastward (see right black arrows on last graphic above), the SRH/CAPE potential was very close to the red curve on the SRH/CAPE diagram above, signaling a much greater tornado threat there. So the May 25th situation was not a simple one to assess. But use of the tools above were definitely helpful in indicating the increased tornado threat and tornado risk as one moved well east and southeast of Kansas City.

To be clear, I do understand and know that there are many, many tornado warning situations where it is essentially impossible to distinguish between warning and not warning using radar in combination with environment conditions... in those cases the environments are simply too "borderline" to make such calls given the knowledge and observing situations we have. BUT, there are also situations where tornado environment parameters are clearly impressive as thunderstorms form, suggesting increased risk of death and injury over larger areas. Those are the times when we need to do everything we can to convey the true risk to the public.

I do also know that many people still don't seem to know the difference between a watch and a warning (maybe the term "alarm" instead of "warning", avoiding the "waa.." word sound confusion between the two words, would be better?). So I often get arguments that much of our populace is too "dumbed down" to deal with a 2-tier warning system. But is that really a reason to continue status quo in our current system when today's technology and knowledge can offer more information in many warning situations? That is something to think about.

- Jon Davies 9/26/11

The 8/13/11 Indiana stage collapse -- an example of severe weather safety issues at a large public venue

2011-08-15T10:30:00.000-07:00

Saturday evening's stage collapse due to strong gust front winds at the Indiana State Fairgrounds in Indianapolis killed 5 people and finished off a week when several people were killed in the U.S. as a result of thunderstorm winds. On Aug. 7, 1 person was killed in southern Missouri when a tree blew onto their car; on Aug. 9, a UPS driver was killed in northeast Indiana when a tree fell on his truck, and on Aug. 10, a woman was killed east of Tulsa OK when thunderstorm winds destroyed a mobile home (this may have been a brief non-supercell tornado from a bow echo on radar). This all serves as a reminder that severe thunderstorm/squall line winds can and do kill people.

Concerning Saturday's Indiana State Fair tragedy, here's what my wife Shawna posted on Facebook:
"The Indiana Governor called last night's stage collapse a "freak accident". I respectfully disagree. That was a make shift stage sitting right in the path of that gust front. It doesn't take a genius to know it was disaster in the making (especially when you see Ernie Mill's photos of the shelf cloud as it approached). The concert should have at least been delayed once the warning was issued (10 minutes out) with an orderly evacuation AWAY from that stage. Very sad and preventable incident. It's also another reminder that we in the weather community need to continue to educate the public about weather awareness."

I agree... At 8:39 pm EDT, NWS had issued a warning for Indianapolis concerning thunderstorm winds in excess of 60 mph a full 10 minutes before the storm struck the fairgrounds at around 8:50 pm EDT, and severe thunderstorms had been in the area west of Indianapolis approaching for more than an hour before (see radar images above). A shelf cloud (a visual "red flag" to watch for strong wind gusts, see Ernie Mill's photos above) was quite visible as the thunderstorm gust front approached the fairgrounds. A full evacuation wasn't practical or even necessary, but certainly it should have been clear that the _temporary_ stage structure with its top-heavy lights was a dangerous place to be around in strong winds. The deaths all occurred in the first several rows as the stage structure collapsed. Someone at a microphone should have emphatically told concertgoers seated within a couple hundred feet of the stage to at least move back well away from the stage structure _before_ the gust front hit; that much would not have been difficult to do. From this perspective, Saturday's tragedy was preventable and certainly not a "freak accident" or "fluke".

At all public outdoor venues that involve thousands of people, the organizers/managers of the event on-site need to be in consistent touch with a meteorologist or weather-knowledgeable person regarding any potential severe weather that may be approaching, even if it is many miles away yet. And a _clear_ communication line needs to be open to those on stage or in control of the public sound system at the event to let people know where to go in a timely manner before weather hits. While full evacuations may not be practical or possible, people definitely need to be warned and told to move away from dangerous _temporary_ structures that may collapse when gusty thunderstorm winds hit them. That seems like a no-brainer.

- Jon Davies 8/15/11

Do we warn too much? Some thoughts on tornado warnings in this tragic year of tornado deaths...

2011-07-30T16:44:00.000-07:00

It's been 2 months since the horrifying Joplin tornado (death toll now 159), and 3 months since the shockingly deadly tornado outbreak in the Dixie states that killed well over 300 people. It now looks like 2011 will be the 4th deadliest U.S. tornado year on record. I don't think most people have any idea how jaw-dropping that is... one has to go way back before a coordinated tornado warning system was in place to find annual tornado death tolls of that magnitude!

When big tornadoes hit cities, there will be deaths. And there have been many large long track tornadoes this year in populated places. But the staggering death tolls this year also raise some questions, including these: Are people getting complacent regarding severe weather preparedness? And do we now warn so much that warnings sometimes fall on deaf ears? A respected nurse at one of the hospitals in Joplin told me, "We get warnings and sirens all the time... we're, like, tone deaf... it's hard to take them seriously." I've heard many similar comments from other people. Severe weather education is a never-ending task that requires continued attention and priority, and getting people to listen and take action is deeply rooted in social science rather than meteorology.

It is noteworthy that, compared to the 1980s, the number of tornado warnings in some parts of the U.S. (such as the Southeastern states) has increased at least seven or eight-fold, according to a recent article in the Birmingham News, while false alarms are averaging close to 80%. I know of no concrete social studies that have examined "warning fatigue" regarding tornadoes and severe weather. Yet I do agree with respected Birmingham TV meteorologist James Spann's recent comments that have stirred some controversy.

I continue to see a number of tornado warnings issued in marginal settings where, based on years of data and increased operational knowledge about tornado environments, the atmosphere can only support, at best, weak or brief tornadoes. In those cases, the threat is considerably less compared to days like the Joplin tornado event this year, and the Dixie Super Outbreak. Yet it is often difficult to discern the relative degree of threat or risk in the text of many warnings, whether read verbatim or presented via media such as television. I know that the National Weather Service (NWS) and television/media meteorologists have a sincere desire to save lives and have the public know about all weather threats. Yet I wonder if we shouldn't reaffirm that we can't warn or cover all severe weather events. Instead, shouldn't we make a stronger effort to emphasize warnings in those weather settings that clearly have potential to be truly dangerous to many people in populated areas? I'm no expert in social science, but with my background in severe weather research, here are some comments from a meteorological perspective.

The first graphic above shows combinations of low-level wind shear (storm-relative helicity or SRH) and instability (CAPE, or convective available potential energy). On the most simplistic/basic level, these are the most important environment ingredients linked to supercell tornadoes based on research over the past 25 years. On this graphic, I've plotted estimated SRH/CAPE points (using nearby RUC model analysis soundings) for 44 tornadoes that were associated with 4 or more deaths over the past 11 years. I've also drawn in a curve suggesting a rough lower "limit" to SRH/CAPE combinations that generally support tornadoes that can kill larger numbers of people; note that all events but one (98%) fell above this curve.

Looking now at a much larger database (2214 supercell soundings I've collected over the past 11 years, 90% associated with NWS tornado warnings), the 2nd graphic above shows the percent and number of both non-tornadic and tornadic supercells (tornadoes shown by EF-scale intensity) falling near and above the red curve in the first graphic, suggesting more favorable SRH/CAPE combinations for strong/violent tornadoes. Notice that, using the discriminating curve suggested by the first diagram, only 17% of the non-tornadic supercells were "false alarms", falling near or above the curve but not producing any tornadoes. But moving over to significant tornadoes (EF2-EF5), notice that increasing majorities of these supercells fell into the more "favorable" area above the curve. Using only this simplistic SRH/CAPE scheme in supercell settings, this suggests workable false alarm and detection rates for supercell tornadoes, not even considering other ingredients such as deep-layer shear, cloud base height, amount of convective inhibition, storm motion relative to surface boundaries, etc., that have been found relevant in tornado forecasting research.

This isn't really new information; forecasters at SPC have used SRH and CAPE combinations along with forecasts of other ingredients for years now when generating outlooks and watches for tornadoes. However, tornado environment ingredients seem to be used less consistently when actual tornado warnings are considered. This is supported by the first column of the 2nd graphic above, where tornado warnings (not shown) were issued for 984 of 1160 non-tornadic supercells, yet the SRH/CAPE environment for 83% of these cases fell below the red curve in the first graphic above. Certainly, supercells in SRH/CAPE environments below the red curve do produce tornadoes, but when they occur, the large majority (80-85% according to my database) are weak (EF0-EF1 intensity). When thunderstorms form and become supercells, it is the environment area above the red curve where the probability of deadly tornadoes increases dramatically.

My point is this: Shouldn't we place a much stronger emphasis on radar-based tornado warnings issued in settings where SRH and CAPE are in the area near and above the red curve in the first graphic above, even prior to confirmed spotter sightings?

There are a variety of ways to work toward this, including better environment awareness by meteorologists (the SPC mesoanalysis page is a great tool in this regard) when issuing and presenting warnings, stronger wording and importance placed on warnings when environments are in the enhanced SRH/CAPE area, and making the public more aware that there are different levels of danger in weather settings.

I know that many of my colleagues in the NWS work hard to incorporate environment information into tornado warning decisions, and that there are many times when it is very difficult to know when to hold back from issuing a warning, or to go ahead and "push the red button". Also, I know that meteorologists in today's media intensive society don't usually get rewarded for not warning in a marginal situation and avoiding a false alarm, but they are ruthlessly scrutinized when a notable severe weather event is missed. I'm not suggesting that we don't warn in marginal situations where tornadoes can still produce isolated damage and threat. I am saying, let's make sure to put the strongest emphasis on warnings in environments where ingredients appear more optimum for stronger supercell tornadoes, and try to be more clear about that to the public.

A 2-tier warning system that would use an enhanced danger "red flag" in larger SRH/CAPE combination situations would certainly be a more radical solution, and require more public education. But this could help hospitals, factories, and public venues make more informed decisions regarding costly labor-intensive sheltering in the more dangerous situations, and possibly reduce apathy from "false alarms". It also might help emergency managers make more informed decisions regarding the use of sirens, maybe running them longer and more consistently in "red flag" situations, or using different siren tones to catch people's attention.

Several of my colleagues have told me the above would be unworkable, and even confusing to the general public. That may be. But I do feel strongly that we can do more to help the public recognize warning situations that clearly have greater danger affecting more people. I can't avoid a strong sense that, with all the information and knowledge available to meteorologists today, we can do a better job conveying true tornado threats to the public and reducing false alarm perceptions that can engender public apathy. I think this is worth at least a look in this tragic year of tornado deaths.

In a future post, I'll discuss some recent example cases that relate to the above discussion.

- Jon Davies 7/30/11

Unusually strong cold-core tornadoes in KS and NE - 20 June 2011

2011-06-21T03:19:00.000-07:00

I had intended not to write about so-called "cold-core" tornado settings (see this paper) for quite awhile, as most tornadoes associated with such settings are weak. Given the terrible death tolls from violent tornadoes in 2011, I feel the main focus should be on settings that produce stronger tornadoes and how we might reduce the number of deaths. But the prolific cold-core tornado event on Monday 6/20/11 in northwest KS and south-central/central NE was atypical; some of the tornadoes were strong in intensity (preliminary rating EF3, rare for tornadoes in a cold-core setting), so I felt a short write up might be justified here.

Many cold-core events start relatively early (late morning or early afternoon) due to the strong dynamics and cold air aloft. The 20 June setting was no exception. The first tornado report came near Quinter KS at late morning just northeast of the surface low, and large tornadoes were in progress in the Hill City/Norton area of Kansas by early afternoon (see Mark "Storm" Farnik's impressive photos above near Long Island KS after 2:00 PM CDT, see also David Mayhew's awesome photo above from the same storm; go to this link for an incredible sequence of his images). Tornadoes continued along a corridor into south central NE with this and another supercell, and other tornadoes occurred at late afternoon with yet another supercell in central NE near York. All these tornadic storms were northeast of the surface low near the warm front/dryline interface, a typical focus area for cold core tornadoes with the closed mid-level low and associated cold air aloft not far to the west.

What made this event so prolific with strong rather than weak tornadoes? I modified the RUC analysis sounding at Hill City at 1900 UTC (2 PM CDT, 3nd image above) for surface inflow parcels coming into the tornadic cell north of Hill City at that time on north or northeasterly winds (see surface observations northeast of the surface low on the surface map above at 1930 UTC). This resulted in an unusual amount of CAPE for a cold-core event, on the order of 2500 J/kg (most cold-core events are associated with CAPE values less than 1000 J/kg). In addition, 0-1 km storm-relative helicity (SRH) was sizable, in the range from 200 to 300 m2/s2 within a focused area ahead of the storm. This resulted in large energy-helicity index values (0-1 km EHI greater than 3.0, see 5th image above) in a corridor ahead of the tornadic storm, also unusual for a cold-core event. The sharp trough and tight closed mid-level low moving into the KS/NE area were unusually strong for mid to late June (see NAM forecast for midday above), a time when, unlike early spring cold-core events, large CAPE values can be present with surface dew points in the 60s F or higher. This large CAPE and SRH certainly provided support for larger and longer-lived tornadoes on 6/20/11 than typically associated with most tornadic cold-core events.

NOTE: Cold-core events aren't defined by whether the storms are "mini-supercells"; yesterday's case featured larger storms that were essentially classic supercells because of the larger/deeper CAPE, contrasting with early spring or fall cold-core systems that may have surface dew pointsonly in the 50s F. The important issue is the _pattern_, with the closed low aloft that organizes intersecting boundaries in a fairly narrow corridor ahead of the surface low and cold air aloft as the midlevel system moves east or northeastward, setting the stage for potential rapid tornado formation. This is a common repeating pattern with cold-core systems that produce tornadoes, and can be very useful operationally in anticipating such events.

An additional factor on 6/20/11 was probably steep low-level lapse rates in the vicinity of the tornadic storm at early afternoon over northwest Kansas. On the last SPC mesoanalysis graphic above, notice the axis of steep lapse rates extending through the surface "dry slot" over western KS into the environment of the northwest KS tornadic storm at 1900 UTC, along with plentiful 0-3 km CAPE. This combination could enhance stretching in low-levels that would already be rather strong due to the cold air aloft from the nearby midlevel low, even as cloud bases might rise some with this hotter/steep lapse rate surface air mixing in from the east from the surface dry slot (again, see surface map above). Indeed, many of the tornadoes formed quickly and were "dusty" (see the Mayhew and Farnik photos above), suggesting non-mesocyclone stretching processes similar to "landspouts", but combining with supercell processes involving strong SRH (see SRH field, also in the last graphic above). According to both Storm Farnik's and David Mayhew's descriptions, multiple dusty tornadoes were sometimes in progress simultaneously in close proximity, suggesting that enhanced low-level stretching processes were ongoing in the northwest KS storm environment northeast of the surface low.

Thankfully, there have been no reports of injuries with any of Monday's tornadoes so far, even though damage as high as EF3 in intensity was observed with at least one of the tornadoes in northwest KS.

Thanks to "Storm" Farnik for sharing his excellent photos and descriptions, and to David Mayhew for allowing me to use one of his images. Check out David's awesome and beautiful sequence of shots from this tornadic storm at:
http://davidmayhewphotography.com/~dmphoto/lightbox/index/category/gallery|StormChaseLog|2011ChaseLog|110620NortonKSnew

Jon Davies - 6/21/11

The Joplin tornado environment - poor visibility with large shear & instability

2011-05-27T15:15:00.000-07:00

The death toll from last Sunday's horrendous and tragic EF5 tornado in Joplin, Missouri (see my prior blog discussion) is now up to 132 people, according to reports on Friday 5/27/11. As the deadliest single U.S. tornado in over 60 years, it is worth taking a brief look at the storm environment that helped generate it.

The RUC analysis sounding for Joplin at 2200 UTC (5:00 pm CDT, see 2nd image above), an estimate of the environment roughly 40-45 minutes before the tornado struck, showed very large instability (MLCAPE > 4000 J/kg) and quite sizable low-level wind shear, with 0-1 km storm-relative helicity (SRH) near 300 m2/s2. This matched values shown on SPC mesoanalysis maps at 2200 UTC (not shown). On the same SRH-CAPE diagram where I plotted the Tuscaloosa AL tornado environment in a blog post a few weeks back (see 3rd image above), this combination of SRH and CAPE places the Joplin tornado environment in the same general area and magnitude on the diagram as the Moore OK tornado in 1999 and the Greensburg KS tornado in 2007, both rated EF-5 as well. Although the NAM 12-hr model forecast under-represented the energy-helicity index values (EHI, combinations of SRH & CAPE; see 4th image above), it did forecast a good estimate of the pattern, with an EHI maximum indicated over northwest AR and southwest MO. So it is not a total surprise that the tornado was so strong and deadly.

What is a surprise is the huge death toll, which was partly a result of the tornado being rain-wrapped and very difficult to see (see my photo at top above), and the size of the tornado (around 3/4 mi wide) going down through a very populated area. Going back to the RUC sounding above, relatively weak winds of 40 kts or less at storm anvil level (around 300 mb or 30,000 ft and above) probably contributed to the high-precipitation (HP) rain-wrapped nature of the storm, allowing significant precipitation to fall in and around the updraft/mesocyclone area where the tornado was located, rather than being blown downwind away from the updraft. This seems a little unusual for an EF5 tornado, as most such environments I have examined (e.g., Greensburg KS and Moore OK) have had much stronger winds at that level, instead of the hodograph doubling back on itself with weaker winds in the 9-12 km AGL elevation range. This exacerbated the visibility issue on a day that was already hazy and murky with moisture and humidity, and may have fed into the number of deaths as residents could not get a visual sense of urgency until the tornado was almost right on them.

Another possible ingredient that may have helped contribute to the tornado was a subtle WSW to ENE boundary that appeared visible in the low-level cumulus field on satellite at early afternoon across the Joplin area (see 4th image above). As the Joplin storm complex moved across or "phased" with this subtle feature, it might have provided some focus for the low-level wind shear and SRH to help spin up the tornadic circulation. But this is only speculation.

The last point I'll make is the complex evolution of the Joplin storm, as can be seen in the radar images in the last graphic above. The original supercell and mesocyclone formed near Parsons KS, but began to fall apart shortly before 5:00 pm CDT over northern Cherokee County KS. At this time, three new cells were rapidly developing on the original storm's right/southern flank; two of these cells ("A" and "B" in the images above) quickly merged, while the southern-most of these newer cells ("C") generated a new mesocyclone around 5:15 pm CDT that prompted an NWS tornado warning for Joplin proper at 5:17 pm CDT. This new mesocyclone produced the Joplin tornado about 20-25 minutes later as it merged into the complex that had been cells A and B. The relevance, if any, of these complicated mergers and rapid evolutions to the intensity of the Joplin tornado is not immediately clear. It can be said that, with each new right flank cell raining into the one to its northeast and merging into the complex, this probably further created visibility problems that helped make the monster Joplin tornado even more deadly.

This intensely tragic event has turned literally thousands of lives upside down. Please consider making a donation to one of several organizations assisting in the Joplin area. See http://www.cnn.com/2011/US/05/23/joplin.how.to.help.

- Jon Davies 5/27/11

Unfathomable - the 22 May 2011 Joplin tornado

2011-05-23T07:39:00.000-07:00

Update, Thursday 5/26/11: The Joplin tornado death toll has risen to 125, making it the most deadly single U.S. tornado since the Woodward OK tornado of 1947. Yet another outbreak of dangerous tornadoes occurred in the Oklahoma/Kansas/Arkansas area on Tuesday 5/24/11, killing several people.

It is now one of the largest single city tornado death tolls in the past 70 years... 89 deaths and climbing. It is the 2nd deadliest tornado event in Missouri history (just behind the 1896 St. Louis tornado in number of deaths). Yesterday's tornado at Joplin, Missouri is yet another massive tragic event in this year of killer tornadoes and huge death tolls.

Shawna and I drove through downtown Joplin minutes before the tornado hit. Sirens were going, but we could not see the tornado, and many people were out and about seemingly unaware or unconcerned. We had been following this storm complex for a couple hours without observing any tornadoes, and though we were a little nervous, we weren't anticipating anything of the magnitude that buried Joplin around 5:45 pm CDT.

We blasted southwest on Interstate 44 to circumvent the approaching mesocyclone on radar that suddenly appeared very strong. As we looked to the north through the trees we caught a brief glimpse of the hard-to-see tornado (see images above, the second enhanced to make the tornado more visible). It was so large and the visibility so poor, that this may have had something to do with why so many people were killed.

Shawna wrote a paper for one of her college classes back in April before the Dixie Super Outbreak on the 27th. In that paper she suggested that, while death tolls from tornadoes have dropped dramatically in the past 50 years due to better warnings and public awareness, that trend might soon begin to reverse again. She noted that "up-close-and-personal" tornado videos may be jading people's attitudes towards the dangers of tornadoes. And, with so many diverse information and entertainment sources distracting people's attention these days, the public may have increasing difficulty "hearing" warnings and grasping the importance of that information through the wall of "noise" produced by our information technology.

Given what has happened in the past month, I wonder if she may well be right. Bonar Menniger's excellent book about the 1966 F5 Topeka tornado, "And Hell Followed With It", details how many people followed and heeded tornado warnings from TV and radio that day (there were only local stations focusing on local information back then). The death toll of only 17 from that evening in Topeka might in some ways suggest a more focused attention and response from the public regarding truly hazardous events back then contrasting with today.

It is clear that the Joplin event was a difficult one to prepare for, with a rain-wrapped hard-to-see tornado forming just west of town when there hadn't been tornadoes from the same storm complex prior to that. And the tornado was huge and violent, around a mile wide going right down through a populated area. But with around 20 minutes of advance warning from the NWS, the death toll is still staggering, and leaves me pondering what could have been done to reduce it. I am so saddened this morning by what has occurred.

I will mention that there were a number of storm chasers who stopped to help with search and rescue in Joplin, including Tyler Costantini and Jay Cazel, Mira Lee, and the Cloud 9 tours group. That's awesome... all those who stopped and helped in the aftermath deserve big credit for doing so.

Shawna's and my thoughts and prayers truly go out to all who have suffered losses in the tornadoes of recent days.

- Jon Davies 5/23/11

The Reading KS tornado - Kansas weather turns deadly on 21 May 201

2011-05-22T08:38:00.001-07:00

Severe weather turned deadly suddenly on Saturday evening 5/21/11 when a tornado struck Reading KS (northeast of Emporia) around dark, killing 1 person, injuring others, and destroying a number of homes. Jim Saueressig's photo above shows the impressive storm structure of the Reading storm after dark.

The environment was one of the most rapidly changing that I've seen on Saturday. At late afternoon, the SPC Sig Tor Parameter (STP) was weak across eastern Kansas with marginal values due to both deep-layer shear and low-level shear being rather weak or marginal for tornadoes (0-6 km shear around 30 kts or less, 0-1 km storm-relative helicity/SRH < 100 m2/s2). This is why SPC issued only a severe thunderstorm watch for northeast Kansas. But by dark, low-level winds had strengthened and backed more than expected, causing much larger shear values, both in low-levels and through a deeper layer. This made STP values sky rocket as the eastern KS environment improved dramatically for supporting tornadoes. See the graphics above comparing STP over Kansas at late afternoon (2200 UTC) with just after dark (0300 UTC), and notice the change in wind profiles from late afternoon to after dark on local RUC analysis soundings at Topeka and Emporia.

The tornado struck Reading around 9:15 pm CDT (0215 UTC), and other tornadoes from the same complex continued to be reported during the following 90 minutes after dark. Notice the RUC 0-1 km EHI and low-level CAPE forecasts above for 0300 UTC, indicating strong CAPE/SRH combinations _and_ a surface-based setting after dark, important ingredients for nighttime tornadoes.

Shawna and I stayed in the local area north of Kansas City watching storms on Saturday evening, and were very saddened to hear about the strong tornado that hit Reading. After an enjoyable week of storm chasing with no deadly severe weather in the plains, last night brought things back to sober reality.

- Jon Davies 5/22/11

A look at 3 plains severe weather settings 5/17/11-5/19/11

2011-05-21T12:18:00.000-07:00

Shawna and I are part of "The Great Tornado Hunt" on The Weather Channel with Mike Bettes and other Severe Studios chasers this month. This blog post looks briefly at the 3 severe weather settings we chased this past week.

The first day involved a landspout tornado in Washington County, Colorado on Tuesday 5/17 west of Cope. We left Kansas City late morning and arrived in Burlington, Colorado late afternoon as a cell blew up west of Akron. Realizing we probably couldn't catch this cell as it headed northward too fast, we drove toward the dryline on I-70 and headed north at Siebert, not expecting much from the mushy looking towers to our west and northwest. One cell did develop a sharp high base, and as we approached Cope, Shawna spotted a dust whirl under it, 10-15 miles to our west. This became a landspout for a few minutes over open country (see photo above). We were lucky to catch it, but a later look back at the SPC mesoanalysis 0-3 km lapse rates and surface-based CAPE fields (see 2nd image above) at 2300 UTC showed the cell we were watching to be in a favorable location where a nose of steep low-level lapse rates (8.0-9.0 deg C per km) and decent SBCAPE values (500-1000 J/kg) were co-located with it on the dryline wind shift. Stretching on the boundary with these ingredients apparently set the stage for a mesoscale accident that we literally bumbled into. The original cell farther to our north was in cooler surface air and less steep low-level lapse rates. Colorado "magic" over elevated terrain is sometimes amazing, with dew points this day only in the low 40s F east of the dryline, but surface heating along the dryline helping to do something interesting!

The next day (Wednesday 5/18) we were tempted to head from Burlington to western Oklahoma where much stronger instability than in eastern Colorado was located, but we weren't excited about the long drive. Looking at model forecasts of the pattern, I noticed that mid and upper level dynamics for lifting were forecast to be much stronger over Colorado, while Oklahoma was near a shortwave ridge at 500 mb / roughly 18,000 ft MSL (see maps in the 3rd image above). Much of that state was also located beneath or south of the southern branch of the polar jet, so I wondered if, even with all the instability, subsidence in that region might keep Oklahoma "capped", or at least keep storms there from intiating until after dark. Because Shawna and I don't get much opportunity to observe upslope storms, we decided to stay in Colorado, and were rewarded with a beautiful supercell that tracked from near LaJunta to Kit Carson, again over gorgeous wide open country (see photos in the 3rd image above). I have to admit we were both surprised that no storms at all developed in Oklahoma, even after dark.

Our final chase day of the week was Thursday 5/19, with a potentially dangerous setting over southern and central Kansas. We started in thick fog that morning at Colby, Kansas, but drove to sunshine in Great Bend at mid afternoon near the intersection of the warm front and the dryline. Signficant tornado parameter values in this area were sizable (> 2.0-3.0, see 4th image above) as storms began to develop just north of Great Bend. But during our afternoon update online with The Weather Channel, both Shawna and Dr. Forbes expressed concerns about the rapid low-level transition in temperatures across the warm front in central Kansas, going from low 80s F to only near 70 F in about 30 miles or so. Shawna also felt strongly that supercells might become high-precipitation (HP) as they moved northeastward into the cooler air north of the front.

I thought the tornado potential was significant, but once again my wife was right! As the cell we followed moved toward I-70, temperatures cooled and the atmosphere became more hazy, reducing visibility. By the time the storm approached Lake Wilson, it was HP in character and hard to see what was going on in the often rain-wrapped area of low-level rotation (see 4th image above). There were possibly some very brief tornadoes in there, but we could not see them, and I have not yet heard any reports of tornado damage from this cell. The contrasting RUC analysis soundings above (last image) at Great Bend and Salina on opposing sides of the warm front showed the issue: low-level convective inhibition (MLCIN) and low-level stability increased rapidly across the front, with large MLCIN making storms increasingly elevated the farther north they moved, even with large low-level shear (storm-relative helicity 300-400 m2/s2). With such a cool low-level thermodynamic environment north of the front, it turned out to be not a strongly favorable set up for tornadoes.

When storm chasing, on most days there are things to learn and refine your knowledge with, if you pay attention :-). And thankfully, there were no strong/dangerous tornadoes in populated areas of the plains last week. Early this next week, Shawna and I will be heading out into the central and southern plains as potential for severe weather and tornadoes picks up again.

- Jon Davies 5/21/11

Cold-core tornadoes in central Nebraska 12 May 2011

2011-05-15T07:25:00.000-07:00

Two weak tornadoes in Nebraska were the first I've intercepted on a "cold-core" storm chase in 5 years, and the first cold-core tornadoes my wife Shawna has seen. Cold-core systems are closed mid-level lows (at around the 500 mb level) that are pools of very cold air aloft, with just enough low-level moisture below them flowing in from the southeast to make the atmosphere notably unstable, although the surface moisture (dew points in the low to mid 50s F) may not appear all that impressive for tornadoes. This event was interesting in that it featured both a landspout tornado near Aurora NE, and a brief supercell tornado near Stromsburg NE.

The surface map and satellite image above at mid-afternoon on Thursday showed a fairly typical cold-core setup (see this paper and this paper for more information about cold-core systems and tornadoes), with a surface low in south-central Nebraska just northeast of the mid-level low, and a boundary intersection area northeast of the surface low in the Grand Island-Aurora-York NE area. This boundary intersection area is often a favored location for tornado development, with a surface heat axis typically protruding in from the south for localized instability enhancement, and low-level shear and helicity often maximized in this area east or northeast of the surface low.

The landspout occurred on a sharp dryline boundary visible on radar as a blue fine line (see third image above) near the boundary intersection area, via non-supercell/non-mesocyclone processes (see this paper). A high-based cell that developed and stetched vorticity on this boundary around 2130 UTC produced a sharp condensation funnel well above ground around 2150 UTC (4:50 pm CDT) that eventually made contact with the surface (see my photos above) with a dust column visible.

A later brief tornado (see last image above) developed with a supercell and mesocyclone featuring much lower cloud bases and cooler surface temperatures farther northeast near Stromsburg around 2340 UTC (6:40 pm CDT) as the boundary intersection area and midlevel cold core system worked eastward. Video of this tornado by Dustin Wilcox can also be found here. This supercell was interesting in that the inflow temperatures were only around 60 F, and the cell structure was rotated 90 degrees counter-clockwise (inflow coming in from the north rather than the east, and the flanking line extending eastward instead of southward from the cell). This made for some spotting confusion at times as cell elements moved northwestward in upper flow ahead of the mid-level low, while new right flank development and eastward evolution of the surface boundary intersection area caused some eastward movement.

NWS Hastings also has some information about the 5/12/11 events here. Thankfully, most tornadoes with cold-core systems are relatively weak (EF0 and EF1) in intensity, as was the case on Thursday with little or no damage reported.

Tornadoes with cold-core systems are rather difficult to intercept, because if there are several cells in the boundary intersection area east or northeast of the surface low, it is hard to know which cell to follow and observe. There are also many issues that can keep cold core systems from producing tornadoes. For example, this same system the prior day on Wednesday produced supercells in northeast Colorado and northwest Kansas, but there were no tornadoes because all cells were occurring north of a sharp stationary boundary where the surface air (40s and low 50s F) was too cold for tornado development.

Computer models are suggesting that yet another cold core system will affect the central plains around the period 5/18/11-5/20/11.

- Jon Davies 5/15/11

27 April 2011: An extraordinary environment for tornadoes.

2011-05-01T08:42:00.000-07:00

Last Wednesday's tragic and historic tornado outbreak (see photos above, and my prior blog post) was unprecedented in the past 75 years of U.S. history, topping even the 1974 "Super Outbreak." The number of deaths are now close to 340 people. It will take a while to sort out the actual number of tornadoes, with NWS surveys ongoing. At least one tornado has been rated EF5 so far (Sunday a.m. 5/1/11).

Why were the tornadoes so strong, so numerous, and on the ground so long? Comparing the 27 April 2011 storm environment to years of tornado database parameters that I've kept, the setting for Wednesday's tornadoes was rare and quite extraordinary.

The scatterdiagram (3rd graphic above) is from research I did with Bob Johns in the early 1990s (Bob is now retired from SPC). We looked at observed soundings associated with 242 F2-F5 tornadoes from the 1980s, and found combinations of storm-relative helicity (SRH, a new parameter at the time that quantitized low-level shear, developed by Robert Davies-Jones at NSSL) and CAPE to be useful in assessing environments with potential for significant tornadoes. Using that data, and with the help of John Hart at SPC, we came up with a parameter called the Energy-Helicity Index (EHI) using the diagram above. EHI is still widely used in tornado forecasting today to assess areas and combinations of SRH and CAPE that can support low-level mesocyclones and, hence, supercell tornadoes.

For reference, on this same diagram above, I've plotted the estimated SRH/CAPE combination points for the deadly 1999 Moore OK and 2007 Greensburg KS tornadoes. I've also plotted the SRH/CAPE environment corresponding to last Wednesday's violent Tuscaloosa AL tornado that killed nearly 40 people (also see the skewT diagram above).

The Tuscaloosa environment location (large red dot) on the scatterdiagram is quite remarkable! It falls in the center and slightly toward the upper right in the area of most optimum SRH/CAPE combinations for tornadoes. Most telling, there are no points on the diagram to the upper right of the Tuscaloosa point, which makes it rather unique. I've looked through my own databases of tornado cases over the past decade, and can't find any tornado environment that even approaches this one (roughly 600 m2/s2 0-1 km SRH _and_ 3000 J/kg MLCAPE). Typically, if SRH is greater than 500, CAPE is less than 2000 (still a very good environment for tornadoes), or, if CAPE is greater than 3000, SRH is only around 200-300 (yet another very good environment for tornadoes). To have both the SRH and CAPE so large, during daytime heating no less (SRH values are usually largest at night with the low-level jet, when CAPE is not so strong), is quite rare and unusual.

Given this information, and the fact that mid-level/500 mb winds were approaching 100 kts on Wedensday (excellent deep-layer shear in addition to low-level wind shear), it is no wonder that tornadoes were strong to violent and on the ground so long. The environment conditions where the storms formed and propagated were probably as optimum as we will ever see!

The final graphic above shows 500 mb maps and 0-1 km EHI conditions approximated/forecast from the RUC model for Monday 4/25/11 (a notable tornado day in TX and AR) and Wednesday 4/27/11 (the historic outbreak). Notice how the midlevel trough stayed in place over the southern U.S. over several days (there were tornado episodes in the South from Sunday 4/24 through 4/27), with the strongest winds peaking on Wednesday (> 100 kts) in association with a strong negative tilt shortwave moving through the trough. Notice, too, from the EHI panels, how much SRH and CAPE were present already on 4/25, setting the stage for the peak combinations on 4/27 with the strong short wave and wind max moving through. The forecast EHI values on Wednesday p.m. 4/27/11 were very large over the MS/AL area, signaling the outbreak to come, though no one could know how historically deadly it would be.

Even with the huge death toll, it must be said again that the National Weather Service and local media did a superior job on Wednesday with outlooks, alerts, and warnings. My heart truly goes out to those who have had their lives destroyed by these tornadoes. I hope anyone reading this will at least consider making a donation to help. See: www.cnn.com/impact.

- Jon Davies 5/1/11

The 27 April 2011 tornado outbreak: A stunning death toll.

2011-04-28T08:56:00.000-07:00

Wednesday's staggering death toll from a huge outbreak of tornadoes in the southern states was truly historic. We haven't seen anything of this magnitude since 1974's 3-4 April Super Outbreak, 37 years ago. I know that news will tend to focus on the number of tornadoes. But a more important statistic sociologically is the _death toll_, which as I write this (on Thursday morning) is being reported to be well over 200 people and climbing!

Ranked by death toll, here are the tornado outbreaks/events with the most deaths in the United States, using Tom Grazulis' landmark reference book, Significant Tornadoes (1993):

Deadliest U.S. Tornado outbreaks/events (total deaths)

747 dead 18 Mar 1925 MO/IL/IN/KY/TN/AL (Tri-State tor 695 dead)
454 dead 5-6 Apr 1936 AR/TN/MS/AL/GA/SC
339 dead 27 April 2011 MS/AL/GA/SC/AR/TN/NC/VA ******
330 dead 21-22 Mar 1932 IL/IN/KY/TN/MS/AL/GA/SC
324 dead 23-24 Apr 1908 TX/AR/LA/TN/MS/AL/GA
317 dead 6 May 1840 Nachez MS (no records on other tors that day)
307 dead 3-4 Apr 1974 MI/IL/IN/OH/KY/TN/WV/VA/MS/AL/GA/NC
305 dead 27 May 1896 MO/IL (St. Louis tor 255 dead)
256 dead 11-12 Apr 1965 IA/WI/IL/IN/MI/OH
217 dead 8-9 May 1927 NE/IA/MO/IL/IN/MI/TX/AR/LA/KY

(Sunday 5/1/11 update: The death toll is now officially at 339, putting the 27 April 2011 outbreak at #3 on the list above, an incredible and tragic event in U.S. history, particularly in our day and age.

******News sources are reporting the 27 April 2011 outbreak as the 2nd deadliest U.S. outbreak on record. Although it may be the 2nd largest _single day_ tornado death toll, the 5-6 April 1936 outbreak, which featured the Tupelo MS tornado [216 dead] and the Gainesville GA tornado [203 dead] only 11 hours apart with 454 total deaths, certainly tops the 27 April 2011 death toll at this point. Our news media today would certainly have reported those 1936 events as one outbreak, so that's why I have the 27 April 2011 outbreak at #3 behind the 5-6 April 1936 events.)

Notice that all but the 1974 Super Outbreak, the 1965 Palm Sunday Outbreak, and yesterday's outbreak occurred more than 50 years ago when a tornado warning system did not exist. Undoubtedly, the death toll would have been worse without excellent forecasts/warnings by government and private meteorologists (see yesterday's SPC outlook above), and excellent information dissemination by the media. National morning news I watched on Wednesday, such as CNN, was strongly highlighting the dangerous situation to come over the South.

However, the number of deaths from Wednesday's outbreak in an age where technology and information exchange are better than ever does raise questions from a sociological standpoint, as my wife Shawna is quick to point out. How many deaths occurred in areas of low-income structures (e.g., mobile homes) where people did not have ready access to shelter from fast-moving storms? Did many people killed not have safe places nearby to go (e.g., below ground)? Were some people not paying attention or not have access to warning/awareness information, and not know about the high tornado risk on 27 April 2011? What was the general level of severe weather awareness and safety knowledge of many of those injured or killed?

Tornado warnings and forecasts are quite good these days with our knowledge and technology, particularly on days with big weather threats over large areas. The watch/warning system did its job quite well on Wednesday. It's also true that there are some situations where people can do all the right safety/shelter actions and still get hurt or killed. But the stunning death toll from the 27 April 2011 outbreak begs many questions, and screams that this is a prime opportunity to study what we as a society can do to further reduce death tolls in weather and other disaster events. In our superior age of information availability, events within the past 10 years like yesterday's outbreak and 2005's Hurricane Katrina seem to suggest that we as individuals may not be as aware or prepared for disaster as we want to think.

- Jon Davies 4/28/11 (updated 5/1/11)

Massive tornado outbreak from OK to NC 4/14/11 - 4/16/11: Why so big?

2011-04-18T18:49:00.000-07:00

The tornado outbreak last Thursday-Friday-Saturday across the south central into the southeastern U.S. and mid-Atlantic states was pretty eye opening (see photos above). Sadly, more than 30 people died in tornadoes, and there were at least 45 deaths over all from a very strong severe weather system on a 3-day tear.

Why so big an outbreak? The 500 mb forecast charts above show a dynamically intense, broad trough in the mid-levels moving from the central into the eastern U.S. during those 3 days, providing plenty of upward "forcing" in the atmosphere. Most of the tornadoes occurred toward the southern end of the system with plentiful moisture (not shown) available from the Gulf and Atlantic.

Also on the 500 mb maps above, notice how the mid-level flow intersected the blue lines of storm initiation and orientation at a larger angle toward the southern end of the activity each day, often around 70 deg rather than 10-30 deg seen father north. This orientation of the mid-level flow aloft relative to the surface activity tended to make for more discrete and individual supercells in those areas, probably helping the generation of tornadoes. Low-level storm-relative helicity (SRH, not shown) was also very high in these areas, with values of 600-700 m2/s2 (!!!) from AL to NC during the last 2 days of the outbreak. This helped to support strong tornadoes in environments where MLCAPE was less than 1500 J/kg.

A new guideline parameter outputting estimated conditional significant tornado probabilities for more discrete supercells, developed by Bill Togstad (NWS Minneapolis, retired) from a large database of mine utilizing parameters from RUC soundings, performed fairly well in real-time during the outbreak (see last 3 images above). Given that many supercells tended to be discrete on the southern end of this outbreak, the stronger and more deadly tornadoes were mostly associated with probability values of 70-90% or more, as can be seen in the examples above. Along with the size and orientation of the broad upper trough, this suggested very favorable tornadic environments over large areas as the outbreak progressed eastward during the 3 day period.

- Jon Davies 4/18/11

April 9 tornadoes in NW Iowa: Contrasting daytime/nighttime environments?

2011-04-12T19:49:00.000-07:00

Last Saturday's tornadoes in northwest Iowa with a persistent supercell complex over a period of several hours were quite interesting. The town of Mapleton took a direct hit before dark with a large dusty EF3 tornado developing from a rather high cloud base after 7 pm CDT (thankfully, there were no deaths or life-threatening injuries). Then, after a "break" of about an hour, the same supercell reorganized and began producing several large long track tornadoes during a 2-3 hour period after dark (see nighttime video shot above of wedge tornado near Odebolt, from Shawna's and my storm chase that night). It is very fortunate that none of these tornadoes after dark hit towns such as Sac City or Pocahontas directly (see tornado track maps above).

The first weak dust whirl tornado near Onawa around 6:50 pm CDT (see photo above, a "tornado" because it occurred within a mesocyclone both on radar and visually ahead of an RFD, under a condensation funnel at cloud base) was a precursor to the tornado from the same supercell that hit Mapleton about 30 minutes later. The environment at that point had relatively high MLLCL heights (around 1500 m), with an 83/61 F surface ob at Onawa, and a fairly steep low-level lapse rate (approaching dry-adiabatic, see the 00 UTC Omaha observed sounding above) with little MLCIN. The later Mapleton tornado was mainly visible due to thick swirling dust rising from the ground into a wedge shape under a similarly "high" cloud base.

The tornadoes after dark were associated with a somewhat different environment (see 02 UTC Denison IA RUC analysis profile above). Low-level lapse rates were no longer steep, and MLLCL heights had lowered to below 1000 m with diurnal cooling while MLCIN of 50-100 J/kg had built in. However, the low-level jet had intensified to around 60 kts just after dark, at least doubling the 0-1 km SRH present before dark; according to my colleague Andy Fischer, VAD wind profiles from the NWS Des Moines radar suggested that 0-1 SRH feeding the NW Iowa supercell complex may have actually been greater than 700 m2/s2! Additionally, MLCAPE increased (opposing the typical diurnal trend) as moist advection via the low-level jet caused surface dew points to rise 2-3 deg F. The resulting strong CAPE/SRH combinations (0-1 km EHI > 10) along with large deep layer shear (> 50 kts) probably helped updrafts and low-level mesocyclones overcome increased near-surface MLCIN to support significant tornado potential after dark. This environment matched those ingredients typically associated with tornadoes after dark in the Plains, as discussed in Davies and Fischer (2009).

Forecast-wise, this day stood out for 2-3 days ahead of time with consistent model forecasts of strong CAPE and SRH values (see NAM 0-1 km EHI forecast above) coinciding with an area of low-level CAPE (see NAM 0-3 km MLCAPE forecast above), implying a strongly unstable and sheared evening and early nighttime environment that would be relatively surface-based over eastern NE/western IA. The only big question was whether warm temperatures aloft (the "cap", not shown) would spread too far out across the Plains area in SSW to NNE mid-level flow ahead of the deep 500 mb trough in the western U.S. (see NAM 500 mb forecast above) to inhibit convection along and south of a northward moving warm front (not shown).

On the morning of the event, however, the NAM forecast of derived radar reflectivity (see above) strongly suggested storms would fire along and south of the warm front over northeast NE and northwest IA around and after 00 UTC 4/10/11. In addition, the NAM 12-hr forecast 850 mb forecast (also above) showed an early evening S to N low-level jet developing over eastern KS/western MO flowing north into the warm frontal area over northwest Iowa, providing moisture advection and convergence along with excellent low-level shear for tornadoes increasing into the early nighttime hours.

- Jon Davies 4/12/11

An Essay: Gustnado or Tornado?

2011-04-07T07:54:00.000-07:00

My analysis (previous blog post) of the setting for Sunday's "gustnado" on 4/3/11 near Perry KS stirred up different reactions and opinions as to whether Sunday's vortex actually was a "tornado" or not. Nature certainly defies categories made by man, and there are definite gray areas in classifying tornadoes and small-scale atmospheric vortices.

Sunday's "gustnado" was not associated with a mesoscyclone. But a "landspout" (a non-supercell _tornado_ according to the AMS glossary) isn't associated with a mesocyclone, either, and is considered a tornado because the vortex (along a nearly stationary or slow-moving boundary) extends well up into the cloud of the parent thunderstorm, with dust typically extending in a vertical column all the way to cloud base, often under a condensation funnel aloft. Gustnadoes always occur along thunderstorm gust fronts and are more shallow; the AMS glossary definition also categorizes them as "weak" and "short-lived".

To my way of thinking, landspouts and gustnadoes are somewhat similar: They both develop from vertical stretching of an area of slow "spin" or vorticity along a boundary, tightening that into a stronger more well-defined vortex. More prolific landspout and gustnado days also feature a steep lapse rate near the ground that enhances vertical stretching as a result of strong surface heating, similar to days where multiple dust devils form over dirt fields from rapidly rising thermals.

The main difference between landspouts and gustnadoes seems to be the depth of the circulation, and the type of boundary they develop on. True landspouts (one type of non-mesocyclone tornado) tend to develop with thunderstorms on pre-existing stationary or slow-moving wind shift boundaries that are somewhat more "straight" in the vertical where the tightening circulation can extend to greater depths and last sometimes for tens of minutes. In contrast, gustnadoes always develop on gust fronts, typically faster moving boundaries that are more "curved/sloped" in the vertical, so that the tightening circulation can't extend/stretch as deep and is more transient as the gust front moves/advances. See the diagram above that attempts to illustrate this difference.

But.... what if there is a gust front that is not particularly fast-moving and maybe doesn't have so much vertical slope? What if a circulation that develops and stretches on that gust front persists for more that a minute or two, lasting maybe 5 minutes or more? What if it occurs under a high cloud base (for example, above 2000 meters) where it is difficult to see how far the circulation extends upward? What if the circulation becomes rather intense (winds to EF1 intensity) and destroys a small farm building? Do we call this a "tornado"? What exactly is "shallow" and "not shallow", according to the subjective AMS definition?

In 2006, on May 23rd, an "outbreak" of gustnadoes occured along the gust fronts associated with a squall line from southeast South Dakota to south-central Nebraska, with many photos taken by chasers. Dirt from some of these extended dramatically to cloud base, with cloud circulation sometimes visible in the shelf above them (see Verne Carlson's photo above). NWS Sioux Falls called some of these vortices "tornadoes" in their local storm reports, while NWS offices in Nebraska did not (look up the SPC storm report log for 5/23/06). Here's another situation the same year, April 24, 2006: A supercell storm produced a mesocyclone tornado near El Reno, Oklahoma. Then, a few minutes later, a non-mesocyclone tornado occurred south along the supercell gust front (see Aaron Kennedy's photo above), which, with little temperature contrast, was barely moving and oriented more "vertical" than "sloped". This tornado had a well-defined condensation funnel with dirt extending upward to it and the clear appearance of a "landspout", even though it was technically on the storm's gust front.

From the above, you can see where man-made definitions and categories fail us, and how difficult it is in some situations to decide how to categorize an atmospheric vortex associated with a thunderstorm. I'll certainly admit that there may be a gray area about how to "categorize" Sunday's vortex. The apparent processes involved with the location of the circulation on a rather fast-moving gust front argue for calling the vortex a gustnado. But the high cloud bases and inconclusive photography regarding how far the vortex really extended upward in the vertical also muddy the waters regarding classification. So there's not a clearly definitive "answer", and we may have to accept that.

With the vortex persisting for awhile and doing some damage, I can see the desire to call such a vortex a "tornado", and I can't completely argue against that. If that were the only criteria, several "gustnadoes" this author has seen and reported were really "tornadoes". Had there been other tornadoes that captured the video spotlight on Sunday that were clearly supercell/mesocyclone in nature, I doubt that discussion would be so focused on this issue right now. For storm chasers, it is always more impressive to see what is categorized as a "tornado" than what NWS calls a "gustnado".

Arguing about how to categorize Sunday's vortex maybe misses the real point. Sometimes, there just aren't exact clear-cut answers, and nature certainly doesn't care what we call something. Perhaps we should just be aware and recognize that there are a wide variety of atmospheric vortices that we don't fully understand or know how to categorize exactly. For research meteorologists, my wife calls this "job security" :-).

- Jon Davies 4/7/11

Big gustnado near Perry KS on 4/3/10 - not a tornado!

2011-04-05T18:41:00.000-07:00

Sunday's (4/3/10) storms over northeast KS featured a supercell that developed near Manhattan around 6 pm CDT (2300 UTC) north of a surface front. There was enough of a "cap" present that it took northward lift over the frontal surface to initate storms, even with temepratures near 90 F south of the front. As the Manhattan supercell passed N of Topeka and moved into Jefferson County northwest of Lawrence, the gust front extending south of the cell managed to tap very warm surface air south of the front, and a large well-organized gustnado (see photos above at top) formed near the intersection of the surface front and gustfront, east of Perry KS and well south of the supercell's mid-level mesocyclone.

Scott Blair has excellent photos and analysis at www.targetarea.net/apr311.html, and NWS Topeka has a good discussion here.

The large gustnado (a relatively shallow gust-front vortex compared to a tornado; see diagram above) probably would not have happened if the supercell gust front had not been able to access the steep low-level lapse rate air south of the surface front. On the radar images above (and a radar loop on the Topeka NWS site), you can see where the supercell was intially all north of the surface front. But as it moved east, the extreme south end along the gust front began to pull in true surface-based air near the frontal boundary-gust front intersection. Note that the observed sounding at Topeka prior to 7 pm CDT (0000 UTC, see skewT graphic above), before both the surface front and gust front passage, showed a very steep temperature drop off in the lowest 2-3 km, a lapse rate that meteorologists would call nearly "dry-adiabatic". Such lapse rates are associated with dust devils and rapidly rising thermals on hot sunny days. In this case, it appears that this air helped with low-level stretching along the gust front near the boundary intersection area, creating a rather intense vortex on the gust front.

Note on the radar image above that the gustnado location was well removed from the mid-level mesocyclone area of the supercell to the north (the wide video image by Connor McCreary above also shows the shallow gustnado occuring along the flanking line/gust front). I've heard some people online claim this to be a "true" tornado, but real understanding of the cell's geometry shows that it was _not_ a tornado, according to accepted definitions of gustnadoes. Gustnadoes can also often occur on days with LCL heights above 1600-2000m (like on 4/3/10), while true supercell tornadoes generally do not.

I've also heard some people claim Sunday's gustnado was definitely a "tornado" because it had multiple vortices. Well... that means nothing; many gustnadoes have multiple vortices. See the last set of images above taken on a storm chase south of Lubbock last June 14th with my wife Shawna and also Anna and Bill Stromberg. Dozens of gustnadoes occured along a storm gust front that hot Texas day, including some with multiple vortices (see the first 6/14/10 photo by Anna and Bill). Some of the gustnadoes were relatively large, too, with organized rear inflow jets, as can be seen in the 6/14 images.

This particular gustnado on 4/3/10 was large enough and well-organized enough to do some damage, and has certainly gotten plenty of air play on TV in view of the lack of real tornadoes that day. Gust front vortices can be very interesting!

- Jon Davies 4/5/11

3-21-11 and 3-22-11 storm forecasts - the "cap" made so much difference!

2011-03-23T18:00:00.000-07:00

With a big trough in the west ejecting waves of energy into the Plains early this week, at first glance, both Monday 3-21-11 and Tuesday 3-22-11 all looked to be possible severe weather days over the KS/NE/MO/IA area. But the "cap" (warm temperatures advecting/moving northeastward from the desert southwestern U.S. in southwesterly flow aloft, called the "elevated mixed layer" or EML) made all the difference between the 2 days. Monday was a bust, with the EML completely inhibiting surface-based thunderstorm developing. But a strong wave in upper flow on Tuesday quickly eroded the EML and allowed storms to fire, some becoming tornadic over Iowa (see pics above from my storm chase with Shawna on Tuesday in the Bridgewater-Greenfield, Iowa area)

When looking at model forecasts for upcoming days, 700mb temperature forecasts can be useful in gaging when the "cap" may be too strong for storms to form. I like to use the chart above as a very rough guideline east of the high plains. In March, 700mb temperatures around 5 deg C (see the chart) are usually warm enough to completely inhibit storm development, unless one is in the high plains with a moist easterly upslope wind to provide mechanical lift (for example, last Saturday evening 3-19 around Lubbock TX - not shown -, where a couple supercells formed), or daytime temperatures become unseasonably warm (for example, 90's F).

The first 700mb forecast graphic above shows NAM and RUC forecasts for Monday evening (00 UTC 3-22-11) from the UCAR online site. Notice how temperatures 5 deg C and warmer on both models were forecast to extend all the way to the NE/SD border, blanketing the central plains in warm air aloft. As a result, Shawna and I did not chase on Monday, with MLCAPE all "tucked" in under this warm air aloft. No daytime storms formed across the KS/NE area due to this strong cap, even though appreciable MLCAPE was present south of a warm front (see the first panel of Earl Barker's RUC CAPE forecast graphic above at the same time). The 2nd 700 mb forecast graphic above shows NAM and RUC forecasts for Tuesday evening (00 UTC 3-23-11) that were dramatically different from the day before, with a strong upper wave moving through the plains, removing the "cap" over KS/NE/IA as much cooler temperatures aloft poured in (notice how the 5 deg C line was forecast to move well southeastward from the day before). This energy and cooling aloft easily triggered thunderstorms in northern KS and eastern NE during the afternoon that moved eastward into Iowa where combinations of MLCAPE (see the 2nd panel of Earl's RUC CAPE forecast above) and low-level shear (not shown) were favorable to support a few tornadoes.

Use the 700 mb temperature chart above as only a rough guide, and not a hard and fast rule. The most helpful thing is to watch _trends_ (for example, how the temperatures around 5 deg C and above moved out into the plains and increased aloft on Sunday 3-20 and Monday 3-21 on model forecasts, then retreated again with the approach of the strong wave on Tuesday 3-22). And don't think that temperatures cooler than the guidelines in the chart mean that storms will defintely occur! On Sunday 3-20 (not shown), 700 mb temperatures cooler than 4-5 deg C were over northern MO and IA, but storms did not develop along a weak frontal boundary. This was probably due to subsidence (sinking motion) behind a short wave that had moved across the Midwest earlier in the day, and boundary layer moisture that was not that deep or rich.

Hopefully the above helps some chasers be more aware of the trending of temperatures aloft and the "cap"/EML over the plains... that can really impact storm potential.

- Jon Davies 3/23/11

ChaserCon Forecasting Class, an Oscar-winning Storm Chaser, & New Book on the 1966 Topeka Tornado

2011-03-04T19:27:00.000-08:00

Wow... tonight it has already been 2 weeks since I taught a tornado forecasting class for the first time at the National Storm Chaser Convention (ChaserCon) in Denver (see pic of me above). It was fun to do, well-received and well-attended (110 people), and I've had several attendees ask about access to some of my Powerpoint slides. I've managed to whittle down the presentation and put a subset of the slides online. If you were one of the people who paid to take my class, send me an e-mail at davieswx@gmail.com, and I'll direct you to the URL address where you can find these.

On another subject, Bill and Anna Stromberg are good friends who work in the film music business in the LA area, and they love to storm chase. Amazingly, Bill's brother, production/art designer Robert Stromberg, won his 2nd Oscar in a row last Sunday night for his work on last year's Alice in Wonderland ! Bill and Anna's storm chasing bug has caught Robert a bit, who was kind enough to share his photos through Bill on this blog last November when he was the only one to document what looked to be a rare morning tornado near Bakersfield CA. Go back and check those pics out here. Congratulations on your Oscar win, Robert!

Last but not least, on Wednesday night 3/2/11, our Kansas City AMS chapter had author Bonar Menninger as a guest speaker on his new book about the deadly 1966 Topeka tornado, And Hell Followed With It (see image above). This is an awesome account of a seminal tornado event that was the first $100 million tornado, grabbing a nation's attention. It was also one of the first events to take full advantage of a relatively new tornado warning system in our nation. Menninger's book relates some searing experiences of people whose lives were literally turned upside down by this tornado. It's important for storm chasers and weather enthusiasts to be reminded how terribly serious and gut-wrenching some weather events can be... weather is not all "fun". This book does that very effectively. Topeka storm chaser and friend Rick Schmidt helped provide some photos for the book taken in 1966 by his father, Topeka Daily Capital photographer Delmar Schmidt. It is a gripping read and an important book documenting a key weather event! I strongly recommend it. Check out the web site at www.topekatornado.com.

- Jon Davies 3/4/11

The U.S. megastorm of 1 Feb 2011 - Why no tornado outbreak?

2011-02-03T16:26:00.001-08:00

The big storm on Feb. 1st that affected much of the central U.S. and Midwest with blizzard conditions and massive snow (see photo above of snow shoveling pile at my house N of Kansas City) was quite a news maker, with several deaths blamed on the dangerous conditions. Often, such strong winter systems (in this case, an intense negative tilt wave moving northeastward out of a large trough, see 500 mb chart above) plow up enough moisture, wind shear and lift to generate an outbreak of tornadoes somewhere in the southern U.S. near the Gulf coast. I heard meteorologists on TV mention the "T" word as a possiblilty in the Deep South several times as this storm intensified. But so far, only 3 weak/brief tornadoes have been reported where several tornado watches were issued. Why the lack of tornadoes on the south end of this intense system?

Using Mobile AL as a spot check location with scattered storms approaching at mid afternoon on Feb. 1st (see 3rd graphic above showing radar and tornado watch in the Mobile area), I saved some RUC analysis soundings at 2000 UTC (2 p.m. CST), using several different parcel lifts (see skewT plots on 4th graphic above). Even though low-level wind shear and storm-relative helicity (SRH) was quite large and seemingly favorable for tornadoes, notice that low-level lifted air parcels from both surface and 1 km above ground showed little if any instability/CAPE (red hatching), and lots of convective inhibition (CIN, green hatching). The most unstable lifted parcel was found well above ground at 2 km (CAPE > 700 J/kg), so that was where the true instability fueling the storms was coming from. In other words, the environment along the Gulf coast appeared mostly _elevated_ in nature, with little instability to be found from air lifted near the ground. This was confirmed by the SPC mesoanalysis at 20 UTC (last graphic above), showing SBCAPE and lowest 1 km MLCAPE to be confined offshore out in the Gulf.

Its been a cold January 2011 with repeated intrusions of Arctic air penetrating southward to the Gulf and cooling the boundary-layer and surface waters. So maybe it's not a surprise that this strong system was unable to pull adequate instability northward at the _surface_ to support tornadoes. Another problem on Feb. 1st was the convective mode, which was largely linear or clumped into complex structures, rather than discrete cells (see radar in 3rd graphic above). Both these factors probably combined to limit the tornado potential. However, with the very strong low-level and deep layer wind shear present (see the Mobile AL hodograph above), it would be remiss for SPC to not alert the public to the possibility of tornadoes via watches, as small increases in CAPE near the coast not forecast by computer models might help support brief tornadoes. Small CAPE/large shear situations near the Gulf coast are often very difficult for forecasters to assess regarding tornado potential, as subtle changes in the low-level moisture profile can make significant differences in the environment.

Jon Davies - 2/2/11

Reed Timmer to speak in Kansas City January 18

2011-01-12T08:27:00.000-08:00

My wife Shawna is currently vice president of the Kansas City AMS/NWA Chapter. She asked me to announce that Reed Timmer from "Storm Chasers" will be our guest presenter at the January 18th chapter meeting! It will be held at Ameristar Casino, 3200 North Ameristar Drive in Kansas City MO. See the flier above.

Reed's talk is "TVN Storm Chasing and Extreme Tornado Research -- the Measurement of Vertical Tornado Winds from Inside the Funnel." He will also have his book "Into the Storm" available for purchase.

This is open to the public. The price is $24.00 per person for both dinner and talk. Make sure to RSVP by January 14 (Friday) 11:00 a.m. by e-mail to my wife Shawna at shawnadavies@gmail.com or to Jim Keeney at Jim.Keeney@noaa.gov.

Storm chasers and weather enthusiasts in the Missouri/Kansas/Nebraska/Iowa area, please pass the word!

Thanks!

- Jon Davies 1/12/11

Long-lived tornadic supercell complex kills 7 in AR/MO 12/31/10

2011-01-05T04:40:00.000-08:00

Killer tornadoes in Missouri are somewhat rare during the month of December, but do happen (5 such events since 1950 prior to 2010). Last Friday's tornado outbreak that left 4 dead in central MO (in addition to 3 dead in northwest AR) was also rare in that the Missouri tornadoes occurred at mid morning (see photos above at Ft. Leonard Wood and Rolla). Another interesting aspect of the outbreak was its evolution from a complex beginning with 2 supercells close to each other in eastern OK into a bow echo structure over eastern MO, persisting for over 6 hours through parts of OK/AR/MO/IL.

The 2nd and 3rd graphics above are regional radar reflectivity composites showing the broad evolution of this complex from 2 distinct long track supercells (circled in white) around 1200 UTC/6 a.m. through 1600 UTC/10 a.m., toward merging into a bow echo type structure after that, with several embedded tornadoes in the St. Louis area around noon. Locations of some stronger tornadoes (EF2+) and deaths are indicated on these graphics. Some of the tornadoes in the latter stages of this complex may have been bow echo/QLCS tornadoes associated with mesovortices instead of deeper mesocyclones. At any rate, this is an interesting example of an event metamorphasis from quasi-discrete supercell mode to a more linear or bow echo mode with embedded tornadoes continuing during both modes.

The environment ahead of the large upper trough (not shown) generating the storms was a classic "small CAPE/large shear" setting so common with winter tornado events. The RUC sounding analysis for 1500 UTC (9 a.m.) at West Plains MO (UNO, see 4nd graphic above) during the hour before the Ft. Leonard Wood and Rolla tornadoes (both from northern supercell, 2 deaths) and Lecoma MO tornado (southern supercell, 2 deaths) showed this, with massive low-level shear and a very large clockwise-turning hodograph/wind profile in the lowest 1 km. Total CAPE of only 400-600 J/kg (620 J/kg sfc-based CAPE) in a close-to-saturated low level environment with little or no convective inhibition (CIN) was more than enough buoyancy to support strong supercell updrafts and deadly tornadoes in such a highly sheared environment.

Composite supercell tornado parameters sometimes have problems working well as indicators in such small CAPE environments. The last graphic above shows the significant tornado parameter (STP, effective shear version) along with radar and surface features around the time tornadoes were occurring in the St. Louis area; notice that not much "sig tor threat" was explicitly indicated over Missouri. Conditional sig tor probabilities (same graphic, same time, developed by Bill Togstad using one of my RUC sounding databases) suggested more tornado potential in the St. Louis area, probably because Bill's equation seems somewhat more "tuned" toward detecting smaller CAPE settings with potential for tornadoes, a nice characteristic, but also one that can sometimes increase false alarms in marginal situations.

At any rate, such a prolific, persistent, and mode-evolving complex (6 hrs+ life span, 7 total deaths) is a rather rare event in the Missouri area, particularly on New Years Eve Day! More survey information can be found at NWS Tulsa, NWS Springfield, and NWS St. Louis sites.

- Jon Davies 1/5/11

Rare EF2 tornado in Oregon 12/14/10

2010-12-15T19:29:00.000-08:00

Yesterday (Tuesday 12/14/10) saw an EF2 intensity tornado strike just southeast of Salem, Oregon shortly before noon PST (2000 UTC) at Aumsville (see photo above), with 2 injuries reported. It's been 17 years (1993) since a tornado that strong occurred in Oregon, and it was only the 4th tornado of F2/EF2 or stronger intensity to occur in the state since the early 1970's. Such events are so rare that they are typically unforecastable, as they usually occur in settings with small CAPE (<> 40 deg F) from western Washington into west central Oregon, and some spotty sun's heating on satellite. Although SPC mesoanalysis graphics showed total CAPE amounts not really registering (less than 250 J/kg, not shown), some low-level CAPE (SBCAPE below 3 km AGL) was indicated over the same area where dew points were maximized (see red areas in 4th graphic above at 1900 UTC). The small tornadic cell formed rapidly around 1910 UTC and began producing a five-mile track tornado around 1945 UTC (see radar inset on 4th graphic).

As is often the case in small CAPE settings, RUC soundings tended to under-estimate the environmental CAPE in this setting, showing surface temperatures around 45 deg F and surface dew points around 40 deg F. However, actual surface observations at Salem at 1900 UTC (not shown) before the tornadic cell formed were 47 F (temperature) and 42 F (dew point). When plugged into the RUC analysis sounding for Salem at 1900 UTC (last graphic above), these updated surface obs combined with cold air not far aloft (-10 deg C at 700 mb !) boosted total CAPE from around 100 J/kg to over 300 J/kg, with the "fattest" CAPE located in the 950-850 mb layer, very close to the ground. Even though total CAPE was unimpressive, this "packing" of CAPE down low in the sounding environment would likely help promote rapid vertical stretching in a local updraft, and given the accompanying sizable low-level and deep-layer wind shear, was able to support a tornadic storm as reported above. But picking out these subtle ingredients in a rapidly evolving environment is more than difficult, and everything apparently had to come together just right to generate a tornado in this case. Another similar setting might generate only storms with small hail. Adding to these problems, rotation in small cells (like this case) more than 25-35 miles from radar is usually not detectable for advance warning purposes.

Although it's not hard to go back and see contributing factors after a climatologically rare small CAPE event like this, detecting in real time these subtle ingredients that might make for a mesoscale "accident" in a location where tornadoes don't often occur is next to impossible.

- Jon Davies 12/15/10

Data collecting inside tornadoes - Will it improve warning lead times?

2010-12-04T21:58:00.000-08:00

The Discovery television show "Storm Chasers" concluded another exciting season this past week. A repeating theme on the show is getting armored vehicles or probes into tornadoes (which makes for exciting storm chase footage) on the premise that this will help improve tornado warning lead times and save lives. But, in reality, that's really doubtful. Chuck Doswell's blog here discusses this issue very well. Measurements inside tornadoes may be useful toward understanding dynamics inside ongoing tornadoes (a valid goal), but will tell us next to nothing about which environments and storms will produce potentially deadly tornadoes. Chuck also points out that warnings for tornadoes most likely to cause deaths are already pretty good. Looking at four tornado days featured this season on "Storm Chasers" that each generated at least one violent EF4 tornado helps drive this point home rather well.

4/24/10 Yazoo City MS EF4 tornado (see photo by Dick McGowan above) - This tornado caused several deaths and was on the ground for 100+ miles in a setting that was well-recognized by NWS meteorologists as having high potential for tornadoes well in advance (for example, see experimental conditional sig tor probabiliities on 1st map graphic above). The specific warning for Yazoo City was issued approximately 30 minutes before the tornado hit town, and warnings for the same tornadic storm farther west had been ongoing for an hour. Can we really improve on those good lead times?

5/10/10 Tornadoes in central OK, including EF4 tornadoes just southeast of Oklahoma City - Again, the potential for this day was outlooked well in advance, with the coming together of environment ingredients quite evident (see 2nd graphic above). Tornado warnings in central Oklahoma were generally issued 30 minutes in advance of damage and deaths.

5/22/10 EF4 tornado near Bowdle in north-central ND - This setting was also quite evident in advance (see 3rd map graphic above), where a large tornado hit mainly in open country. A tornado warning for Bowdle was issued nearly 30 minutes in advance of the tornadic storm passing just northwest of town, and tornado warnings farther west had been ongoing for about an hour.

6/17/10 Tornadoes in MN, including the EF4 Wadena MN tornado - Another setting where tornado environment ingredients were very evident (see last graphic above) in advance, and most warnings were issued 30 minutes before sizable towns were struck.

Here are some representative values of individual bulk environmental ingredients associated with the above cases:

4//24/10 MLCAPE 1950 J/kg 0-1k SRH 670 m2/s2 0-6km shear 70 kts
5/10/10 MLCAPE 3340 J/kg 0-1k SRH 610 m2/s2 0-6km shear 62 kts
5/22/10 MLCAPE 3930 J/kg 0-1k SRH 345 m2/s2 0-6km shear 52 kts
6/17/10 MLCAPE 2525 J/kg 0-1k SRH 270 m2/s2 0-6km shear 54 kts

Any competent NWS meteorologist on days with environment ingredients like those above would be primed and ready to issue warnings immediately at the first indication on radar or credible information from spotters. The next level of improvement regarding saving lives will likely involve sociology to find ways to get people to hear and pay attention to those warnings already being issued.

The Discovery show is about 95% thrills and entertainment, and maybe 5% real science. But it makes interesting watching for legions of viewers, and I do commend the show producers this season for balancing the adrenaline quotient with some sober reality by showing the aftermath of tornadoes, including damage and injuries.

- Jon Davies 12/5/10

November funnels near Bakersfield CA

2010-11-09T15:45:00.000-08:00

My friend composer/conductor William Stromberg (who also storm chases with his wife Anna Bonn) sent me the cool photos above taken by his brother Robert Stromberg (production designer and Oscar winner earlier this year for the film Avatar) yesterday morning while driving on Interstate 5 near Bakersfield, California (about 90 miles north-northwest of Los Angeles). These came out of some very low-topped convective showers associated with a potent upper storm system but limited instability, so I thought the setting was worth a look.

The 500mb forecast during the day on 11/8/10 (see 3rd image above) showed a strong upper trough (heavy black dashed line) moving across California and Nevada. Although a surface cool front (not shown) associated with this trough had already moved through the area, there was just enough moisture (surface dew points in the upper 40s F) and cold air aloft for a little sun-driven surface heating to pop some small showers (see satellite image above) in the Bakersfield vicinity, aided by forcing from the upper system.

A RUC model analysis sounding estimate for Bakersfield (BFL, see last image above) at around 16 UTC (8 am PST, near the time of the funnels), indicated a small pocket of CAPE/instability (possibly under-estimated by the RUC model) at around 3000 ft above ground, which is very near the surface. Apparently, enhanced stretching with the CAPE pocket so close to the ground, a steep lapse rate below cloud base, and the strength of the upper system combined to generate these "cold air" funnels within the updraft columns of 1 or 2 of the low-topped showers. As you can see, you don't always need alot of instability to get interesting things to happen with some fall and winter systems moving across southern and central California.

I didn't see any funnel or tornado reports online with the National Weather Service, so it may be that Robert was the only one to photograph these funnels. Many thanks to Robert and William for sharing these photos of an event that would otherwise have probably gone undocumented!

- Jon Davies 11/8/10

Late October EF2 tornado at Rice TX

2010-10-26T09:29:00.001-07:00

There's been no shortage of interesting tornado events the past couple months, with a tropical system producing tornadoes in the Dallas TX area and a bow echo type tornado in the Queens/Brooklyn area of New York City in September, and damaging tornadoes in the high country of central Arizona in early October. I've been busy, so no case study posts on those events. Last Sunday saw a photogenic October EF2 tornado at Rice TX, southeast of Dallas and just north of Corsicana TX (see storm chaser Bridget Geaughan's photo above). Video shown on CNN from a range of about 100 yds from the tornado was quite impressive. Although there's nothing terribly unusual about an October tornado in Texas, I thought I'd at least post some brief material about the setting to help make up for lack of posts in recent weeks.

Probably the most interesting aspect of Sunday's afternoon setting is how quickly the low-level shear increased during the afternoon in response to the strong mid-level trough (see 2nd image above at 500 mb) moving west to east across Texas that helped fire up the storms ahead of a pre-frontal surface trough and wind shift (see surface map, 3rd graphic above). The SPC mesoanalysis showed 0-1 km storm-relative helicity (SRH, a measure of low-level wind shear, see 4th graphic above) at 2100 UTC / 4 pm CDT to be in the 100-150 m2/s2 range in the Rice TX area, values somewhat marginal for support of supercell tornadoes. However, by 2300 UTC / 6 pm CDT, about the time of the tornado, SRH values had doubled (> 250 m2/s2, same graphic) in response to the approaching mid-level trough, increasing the combination of SRH and MLCAPE (around 3000 J/kg) that could help generate low-level mesocyclones with stronger supercells (energy-helicity index near 3.0 and above by 2300 UTC, same graphic).

The RUC analysis profile at Corsicana TX, a few miles to the south of Rice at 2300 UTC during the tornado (see last graphic above), suggested strong combinations of parameters for supporting supercell tornadoes, even with a surface wind slightly west of due south. So a strong tornado occurring with a discrete supercell in this environment was not a surprise; SPC had a tornado watch issued well in advance, and a tornado warning was issued by NWS Ft. Worth based on radar roughly 15 minutes prior to the tornado.

- Jon Davies 10/26/10

Wind damage (and mesovortex) near my home 8/20/10

2010-08-22T12:08:00.001-07:00

On Friday 8/20/10 while working at home (north of Kansas City), an intense squall line came through and caused an west to east swath of wind damage about two miles south of where I lived. The photos above show sections of corn crops flattened and some tree damage in that swath, damage I wasn't aware of until the next day when my wife Shawna noticed it while driving to Kansas City. There's really nothing unusual about this, except it seems the swath was associated with a forward "notch" in the line on radar, suggestive of a surface circulation with strong winds about 1-2 miles across called a mesovortex. The Kansas City NWS office at Pleasant Hill MO issued a tornado warning (based on this feature) a few minutes after it passed to the south of my house, and wind reports of 70-80 mph winds were verified in Holt MO, about 15 miles to my east. It's not too often a feature like this comes close to your home, so I thought I'd post a little documentation here.

NWS issued severe thunderstorm warnings for Clinton/Platte/Clay counties of MO well before the squall line passed my house. My photos above show views to the south and west as the line approached my home, with a bowing dark cloud shelf to my south and a ragged chaotic cloud base to my west just north of the "notch" on radar (I wasn't aware of the radar feature or damage until later). The forward flank "notch" can be seen on the radar base reflectivity images above (arrows), as well as the low-level base velocity image (circle). It was difficult to pick out a rotational "couplet" with this feature on storm-relative radar velocity images from the Pleasant Hill NWS radar (not shown). However, according to Evan Bookbinder at the NWS office, the closer and more favorably located Terminal Doppler Radar near MCI (KC International Airport, not shown) indicated a pronounced couplet with 80-90 mph winds toward the east on its south side as the feature approached Holt MO, prompting the tornado warning around 1905 UTC. The wind damage south of my home (a swath of 70-80 mph winds) clearly lined up with this radar feature before the tornado warning as it tracked eastward.

A surface map is also shown above, showing the squall line location after 1800 UTC, and surface temps in the 90s F ahead of the line with dew points in the mid-upper 70s F. The early afternoon environment over northwest Missouri (not shown) was quite unstable, with CAPE values near 4000 J/kg, around 30-35 knots of deep layer shear (0-6 km AGL), but little low-level shear (storm-relative helicity less than 80-90 m2/s2). So, the CAPE/shear setting was supportive of strong organized storms (possible supercells) with potential for wind damage, but suggested little support for much in the way of tornadoes. Forward flank squall line circulations in such settings can certainly produce notable wind damage, and even occasional weak/brief tornadoes of non-supercell origin.

- Jon Davies 8/22/10

Rare deadly tornado in Montana - 7/26/10

2010-07-27T14:48:00.000-07:00

Killer tornadoes are rare in Montana due to the sparse population. Prior to 2010, only 2 deadly tornadoes had been recorded in the state, with the last tornado deaths occurring way back in July of 1983. But yesterday (Monday 7/26/10), sadly, 2 people were killed and another seriously injured when a large tornado struck a ranch in the northeast corner of Montana west of the town of Reserve (see photo and radar images above). This tornadic supercell moved east-southeast from Canada, deviating rightward under westerly flow aloft.

The surface map at early evening (above) showed a surface low over northeast Montana with easterly upslope winds along and just north of a stationary front where surface temperatures (80s F) did not cool too rapidly across the WNW-ESE boundary, and dew points feeding the storm were in the mid to upper 60s F. RUC model soundings had a little trouble depicting the moisture depth in northeast Montana near this boundary (moisture too dry/too shallow just above the ground, not shown) and wind profiles (hodographs a little "flat" in shape, not shown). However, the SPC mesoanalysis effective-layer sig tor parameter (STP, see graphic above) still suggested a "favorable" environment not too far to the east over extreme northwest North Dakota, likely feeding into northeast Montana on the upslope winds near and north of the stationary front.

A RUC analysis sounding at early evening near Reserve MT (last image above) had to be modified for moisture depth and the easterly wind pattern in order to be reasoanbly represnetative of the environment. This modified profile showed excellent deep layer shear (60 kts), good MLCAPE (2800-3000 J/kg), and workable low-level storm-relative helicity (SRH, > 150 m2/s2). Even though the low-level hodograph/wind profile wasn't large or notably strong, there was a "kink" in the profile and enough low-level shear to support strong tornadoes along and near the boundary. It appears this tornadic storm was able to parallel the boundary, taking advantage of the enhanced low-level wind environment there, along with better moisture just north of the stationary front without too much temperature contrast across it. Tornado warnings from the Glasgow NWS blanketed the area traversed by the supercell well in advance of it.

- Jon Davies 7/27/10

After-dark EF4 tornado in NW Iowa 6/25/10 - a look at the environment

2010-06-30T05:37:00.000-07:00

Violent (EF4-EF5) tornadoes are rather rare after dark in the Plains. Last Friday's tornadoes during 03-05 UTC 6/26/10 after dark in northwest Iowa (see video image above) included an EF4 intensity tornado near Sibley, Iowa, which certainly makes the environment worth examining.

The tornadoes occurred just ahead of a cool front moving slowly southeastward (not shown) and an approaching upper trough (not shown), associated with the west end cell of a line sagging southward over northern Iowa (see SPC mosaic radar overlays above). The 03 UTC SPC mesoanalysis of 0-1 km energy-helicity index (EHI; see 2nd image above), which combines MLCAPE and 0-1 km SRH, showed very large values (near 10!) ahead of this west-end supercell over northwest Iowa, suggesting strong potential for low-level mesocyclones and possible tornadoes with discrete or tail-end supercells. The SPC mesoanalysis of low-level CAPE (0-3 km MLCAPE, see 3rd graphic above) at the same time also showed a notably surface-based setting over northwest Iowa, with low-level MLCAPE values near 100 J/kg. From a 2009 NWA electronic journal paper by Davies and Fischer, environments with large CAPE and SRH that are also relatively surface-based offer important support for tornadoes after dark, but aren't that common in the Plains due to nighttime cooling beneath typical warm layers advected eastward from the desert southwest. This latter issue did not appear to be a problem last Friday evening over northwest Iowa.

The 03 UTC RUC analysis sounding at Sheldon, Iowa (just south of the tornadic tail-end supercell; see 4th graphic above) confirmed large MLCAPE and SRH (near 4000 J/kg and 500 m2s2) and sizable deep layer shear (> 40 kts), along with a relatively surface-based setting (0-3 km MLCAPE > 100 J/kg, and MLCIN around -50 J/kg), all excellent supporting ingredients for tornadoes with supercells in that environment. In contrast, 110 miles to the east-southeast with another tornado-warned embedded supercell near Clarion, Iowa, the RUC sounding (see last graphic above) showed _no_ low-level CAPE, and MLCIN was quite large (-250 to -300 J/kg) with not nearly as much total MLCAPE above the CIN layer (only around 1600 J/kg),. This suggested somewhat "elevated" nighttime storms with considerably less tornado potential, and no tornadoes were reported in this area farther east.

NWS Sioux Falls has a page detailing their survey of the EF4 tornado near Sibley, Iowa, north of Sheldon.

- Jon Davies 6/30/10

Matt Hughes

2010-05-28T06:57:00.000-07:00

This has been a sad couple weeks with Wichita chaser Matt Hughes (of Discovery Channel's Storm Chasers show) hospitalized in serious condition, and then passing away this past Wednesday. I am so very sorry for his family's loss.

I haven't known Matt for very long, but it is clear he was a bright and enthusiastic person, with much passion, and also very sensitive.

With the deadly Yazoo City MS and Oklahoma City OK tornadoes this year, and now Matt's death, I hope these events will serve as reminders to weather enthusiasts that there are more important things in life besides storm chasing, and to keep all that in its proper perspective.

Matt, we will remember you fondly...

- Jon Davies 5-28-10

Brief "chaser convergence" thoughts, and Missouri cold core tornado setting 5/20/10

2010-05-21T11:18:00.000-07:00

Wednesday's massive chaser convergence and careless driving in central Oklahoma has been a huge topic of conversation the past couple days. Shawna and I actually decided not to chase that day because of the expected chaser hordes and narrow severe focus in central Oklahoma, and we both had work to do. Sometimes one asks, "If there's already hundreds of people out there shooting the same storm, what's to learn and what's the point of being out there adding to the dangerous traffic jams?" Wednesday was just such a day. Things don't look to improve in similar future situations, unless someone gets killed in traffic and it is well documented. Shawna and I are getting increasingly picky about going out on "big" days with a small focus drawing hundreds of chasers and weather yahoos to the same spot.

Anyway, stepping away from the situation in Oklahoma, Wednesday 5/19 brought some "cold core" action to the Garden City/Dodge City area of southwest Kansas in the form of "landspouts" along a surface boundary close to the 500 mb low, photographed nicely by Mike Umscheid. And Thursday 5/20 brought a few "cold core" supercell tornado reports to the Sedalia area in Missouri east-southeast of Kansas City (see photo above). I had family visiting in town, so no storm chasing for me or Shawna. But with my interest in such settings, the Thursday setup is worth documenting briefly. Thankfully, as with most "cold core" setups, none of the tornadoes were strong.

The 2nd graphic above shows visible satellite with overlaid surface and 500 mb features at 2145 UTC. Notice the boundary intersection in west-central MO, similar to the "cold core" tornado composite shown in this paper. This can be a favored area of severe focus (enhanced low-level shear and forcing) for tornado development when a midlevel low (strong cold air aloft) is nearby to the west (northeast KS on 5/20) and there is some instability. In this case, the N-S boundary wasn't a dryline, but a subtle wind shift intersecting the warm front southwest of Sedalia at late afternoon, notable on satellite along with some clearing for sun's heating. The 3rd graphic shows selected images from the SPC mesoanalysis at 2200 UTC , including the midlevel low, total CAPE (near 1000 J/kg over west-central MO, but certainly not as impressive as down in Texas), low-level CAPE (a significant maximum near the boundary intersection), and SRH (enhanced northeast of the warm front, but probably under-represented closer to the front in west-central MO). The presence of the 500 mb low in northeast KS and the low-level CAPE maximum over west-central MO near the boundary intersection were probably the biggest "heads-up" flags seen here for tornado potential in what otherwise looked like a fairly benign environment.

The 4th graphic above is a radar image at about 2340 UTC when the tornado in the photo above (likely EF0) was occuring near Sedalia (see arrow for cell location). The RUC analysis at 2300 UTC (last graphic above), as with many "cold core" type settings, showed most of the CAPE below 500 mb, suggesting sizable low-level stretching. The model-derived estimated hodograph (same graphic) suggested good clockwise curvature to the wind profile and more low-level shear than shown on the SPC mesoanalysis during the afternoon. So, while not an easily forecast event, the presence of these ingredients suggested taking rotational signatures on the nearby Pleasant Hill MO radar and spotter reports very seriously. Indeed, the Kansas City area NWS office did a good job jumping on the situation with tornado warnings and statements as the situation developed and evolved prior to the Sedalia tornado, which is what situational awareness is all about.

- Jon Davies 5/21/10

Monster Medford OK meso & tornadoes 5/10/10

2010-05-15T16:48:00.000-07:00

My wife Shawna, her son Zach, and I intercepted the large supercell near Medford OK last Monday (5/10/10). As a rule, I don't chase storms going 50+ mph, but we decided to try it, given the high-end potential tornado environment (see significant tornado probability mesoanalysis graphic for 20z, 2nd image above, an experimental product that Bill Togstad in Minneapolis and I have been working on). We were prepared for very fast storm motions, probably giving us only a few minutes of intercept time.

There were many chasers on the Wakita-Medford storm, but we managed to avoid most of the crowds (and all the road "drama" south of Wakita) by pulling off on a county road 5 miles north of Medford and letting the dangerous storm come toward us. As it emerged from the haze and broken low clouds near Medford around 3:50 pm, the mesocyclone at first appeared to be rain-wrapped, but then we could begin to see features behind the rain curtains, including a narrow tornado on the north side of the meso (see 3rd image above, please excuse the poor video quality). We were using WxWorx due to some internet problems, and Threat Net was indicating that the meso would pass just to our northwest. Not so! It quickly became apparent that the storm was moving more rightward/eastward, and that we needed to move south FAST, out of the path.

It was unnerving to see a meso that large coming toward us at nearly 60 mph (a mile a minute!), and the pressure drop with the fast movement was causing our ears to "pop", the first time I remember experiencing this with an approaching mesocyclone. As we blasted south, the first tornado dissipated, and a larger one formed near the center of the meso, with rain and dust curtains moving around it. In fact, thoughout much of the meso, what appeared to be wispy "spin ups" and brief condensation columns were also occurring, causing us to wonder if much of the mesocyclone might actually be a very wide lower-end "tornado" a mile or more across, with more intense vortices moving around inside it (see 4th image above). There's certainly no clear-cut answer to that. Regardless, we needed to get out of the way.

As the larger cone tornado within the meso sped toward us (see 1st image above), we cleared the path of the meso and RFD winds to the south, and pulled over just north of Medford. Looking back to our north, the tornado(es) were no longer visible, as rain and hazy sunlight obscured our view (chasers farther east reported seeing only a rain-wrapped meso at this point). Looking to our west, we noticed an anti-cyclonic wall cloud and circulation on the trailing gust front (a feature not that uncommon), whch produced a very brief spin up beneath a small condensation funnel aloft (not shown). With the incredibly fast storm motion, our chase was over in only minutes, and Shawna's son Zach had videotaped his first tornado(es).

The last graphic above is a schematic and approximated path of this large fast-moving mesocyclone (several miles across), one of the largest and fastest I've ever seen. Despite the damage path from near Wakita OK to east of Arkansas City KS, it was great to hear that there were no deaths or serious injuries from this dangerous supercell.

For those on Facebook, additional video captures are under Shawna Davies' photo folder titled "5-10-10 Medford OK meso /tornadoes".

- Jon Davies 5/15/10

Dick McGowan's photos of 4/6/10 Wakeeney KS tornadoes

2010-04-07T20:11:00.000-07:00

Dick McGowan (www.tornadolive.com) was kind enough to send me a few images from his Wakeeney KS chase yesterday, to compliment my earlier post about the meteorological setting for these unusual tornadoes (surface temperature mid 60s F, dew points mid-upper 40s F).

The first image shows the first tornado north of the interstate, with a condensation funnel well aloft and dust circulation at the ground. Dick says this tornado formed rapidly from a bowl-like high-based mesocyclone circulation and lasted maybe 2-3 minutes. The last image shows this tornado dissipating (right) with a 2nd tornado at left in what appears to be an occluded area. Dick says this 2nd tornado lasted about 3 minutes, and even hit a small farm structure, lifting pieces of debris into the air.

Looking back at the Hays RUC profile in my previous post, the high cloud bases and steep low-level lapse rate suggest to me that these tornadoes may have been a "hybrid" type of event, combining supercell and non-supercell processes, with significant heating at the surface (possibly upper 60s F) and very cold temperatures not far aloft (0 deg C around 700 mb). Dick says that he had the visual impression of updrafts that were shrinking horizontally and stretching very rapidly in the vertical as the tornadoes occurred. At any rate, these weak tornadoes occurred in an odd location relative to the surface pattern, away from the deeper moisture, and were the only ones I know of that were photographed over the past 4 days of severe weather in the Plains.

Dick, thanks for sharing these images.

- Jon Davies 4/7/10

Update 4/8/10 AM - I looked back at the surface analysis I did in the previous post, comparing it to Dodge City radar base reflectivity just before 2100 UTC on 4/6/10, and found I missed a boundary (Dick McGowan also mentioned this). I've drawn this in on the updated surface map (with radar) above, suggesting that the Wakeeney tornadoes occurred at or near a pretty decent boundary intersection, which may have added some nice vorticity ("spin").

Surprise tornadoes near Wakeeney KS 4/6/10?

2010-04-07T14:18:00.000-07:00

Although not in yesterday's NWS storm reports for 4/6/10, storm chaser Dick McGowan (on his way to Oklahoma from Denver) happened to be in the right place at the right time, apparently photographing a couple tornadoes near Wakeeney, Kansas, just north of I-70. I haven't seen any pictures posted yet. but this was well northwest of the true warm sector, and in the vicinity of a secondary front moving across northwest Kansas. This wasn't a forecastable event, but it is worth looking at because it was certainly unusual.

The first graphic above is a SPC mesoanalysis estimation of 0-3 km MLCAPE and surface vorticity at 2100 UTC (4 pm CDT), with radar reflectivity overlaid. Notice the pronounced low-level CAPE maximum in the Wakeeney/Hays KS area. By itself, this doesn't mean much, but given its location far away from the warm sector over eastern Kansas, it suggests an area of cold air aloft combined with surface heating. The surface analysis just before 2100 UTC (2nd graphic above) shows an east-west frontal boundary in the area, with surface temperatures in the mid 60s F along this front (70s F further south) and dew points in the mid-upper 40s F. The RUC midlevel map analyses at 2100 UTC (3rd graphic above) definitely show cold air coming in aloft at 700 mb (0 deg C over northwest Kansas) and a closed 500 mb low over northern Colorado. So there was warmth at the surface, cold air aloft at 700 mb, and a frontal zone with just enough moisture in the local area. One probably wouldn't call this a real "cold-core" setting given the odd surface pattern and the distance from the midlevel low, but the cold air aloft with this system certainly played a role.

Visible satellitie and radar (4th graphic above) show the location of a small cell (possibly a mini-supercell) near Wakeeney, moving east, with plenty of clear skies (heating) to its south and east. This is near the time the tornadoes were reported. A RUC analysis sounding at Hays Kansas at 2100 UTC (east of Wakeeney, last graphic above), modified for more heating than the raw RUC file indicated, yields 200-300 J/kg of CAPE, all bunched below 500 mb, with decent wind shear, fairly steep low-level lapse rates, and small CIN. This is another one of those small CAPE soundings I've discussed recently, and the type of environment that would likely generate rapid low-level stretching within local updrafts. Given all the above ingredients, it's not too much of a "stretch" to see how the setting might support some weak tornadoes with the isolated cell over northwest Kansas. But it was certainly not an event that could really be anticipated.

What an oddball case! And as I write this, more cold air aloft from the same system is now generating a small late pm severe cell over north Kansas City, just behind a secondary surface cold front.

- Jon Davies 4/7/10

Another small CAPE/large shear tornado setting: 3/28/10 in North Carolina

2010-04-01T06:42:00.000-07:00

Last Sunday afternoon and evening (3/28/10) in central North Carolina was a great example of a small CAPE setting (300-500 J/kg) that had very large low-level and deep layer shear and was able to support a strong tornadic supercell (see photos above), including an EF3 tornado at High Point, just southwest of Greensboro.

Lowest elevation base reflectivity from radar and a surface map just before 2300 UTC (7 p.m. EDT, see 2nd graphic above) showed this supercell moving northeast near a southwest-northeast stationary front with a well-defined moisture axis (dew points low to mid 50s F) impinging on it from the south. The SPC mesoanalysis at 2200 UTC (3rd graphic above) showed very large storm-relative helicity (SRH) over central NC but only weak/marginal CAPE, with larger CAPE indicated back to the southwest. But as suggested by the moisture axis on the surface map, strong moist advection was definitely taking place across North Carolina.

This case highlights how important it is to update and modify model soundings with actual surface data when estimating environments. The raw RUC sounding at Asheboro (HBI, about 20 miles southeast of the tornadic supercell track, see 4th graphic above) showed only 61/55 F as temperature and dew point at 2300 UTC, but observed surface data indicated at least 63/57 F, which can make a considerable difference in CAPE computation. Modifying this sounding with the observed data (see last graphic above) and using a surface-based lifted parcel (the low-levels were nearly saturated) changed the CAPE from barely over 100 J/kg to well over 400 J/kg, a nearly four-fold increase! Combined with the very large 0-1 km SRH (> 500 m2/s2) and deep layer shear (near 70 kts), this was more than enough to support a significant tornado that caused injuries.

When using model soundings to estimate a severe weather environment, it's vitally important to watch how well the model is performing by checking actual observations, and to make adjustments when necessary... no April fooling!

- Jon Davies 4/1/10

The Alabaster AL tornado on 3/25/10 - a small CAPE setting

2010-03-28T17:07:00.000-07:00

The Alabaster, Alabama tornado a few days ago (Thursday 3/25/10) was another reminder that tornadoes can and do occur in small CAPE environments, sometimes with only 200-300 J/kg of CAPE. Such tornadoes typically aren't very strong (the well-photographed Alabaster tornado was rated only low-end EF-1). A photo of the tornado showing the rear-flank-downdraft and a little structure is seen above. Alabama storm chaser Brett Adair also captured the tornado on video shown on The Weather Channel.

The setting had a sharp short wave at 500 mb (see 2nd graphic above) moving across Tennessee and Alabama, with only low to mid 50's F dew points at the surface ahead of a Pacific type cool front (see 2nd graphic above). Because online model forecasts typically are presented showing only areas of CAPE 500 J/kg and above, plan-view model forecasts and analyses didn't highlight the CAPE present over Alabama (see the 2nd graphic above). But with an NWS office located at Alabaster (the Birmingham area office) that is also a RAOB sounding site, and the tornado occurring just to the west at sounding time, the Alabaster tornado was one of those rare instances where an actual observed sounding was available in close proximity to the tornado-producing storm (see 3rd graphic above). This sounding shows the CAPE all bunched down below 600 mb (about 4 km in the vertical), very low in the profile. Given that this was a discrete cell in an environment with 250-300 m2/s2 of storm-relative helicity (SRH) and the CAPE was squeezed low in the sounding, low-level stretching and tilting probably facilitated the tornado. An interesting low-topped tornadic supercell case to study, and not associated with a closed cold-core 500 mb low.

As I write this, tornadoes with damage have been occurring over the Charlotte-Greensboro area of North Carolina, in another setting with small CAPE (< 500 J/kg) but very large low-level shear.

As I mentioned earlier this month, I had hoped to get a page up showing some interesting pics and graphics of the 1990 Hesston KS tornado 20 years ago. Unfortunately, things have been busy on my end, so that will have to wait awhile :-(.

- Jon Davies 3/28/10

"Cold Core" discussion and comments 3/8-3/10/10

2010-03-12T12:53:00.000-08:00

I've gotten lots of requests to discuss the two "cold core" systems that came through the central U.S. this week. Was the Hammon OK tornadic storm a "true cold-core-type" supercell? Why did the Monday 3/8 system generate tornadoes in western OK, but no severe weather near Kansas City the next day (3/9)? Why didn't the next system on Wednesday 3/10 produce tornadoes in Oklahoma or Kansas? There are not easy, concrete answers to any of these questions. It goes without saying that the atmosphere is enormously complex and something we'll continue to struggle with understanding. I'll try to offer a few thoughts and opinions here in this rather long discussion.

First, labels like "cold core" (coming from Ernest Goetsch's 1988 SLS conference paper, and Mike McDonald's 2000 Canadian paper) are clearly problematic. Labels may help get us in the general "ball park" so that we can begin discussing settings and issues without having to go into long preliminary descriptions each time we mention them. But labels mean different things to different people, and come with very different assumptions depending on the person and their experience. Certainly, the atmosphere doesn't recognize labels or behave according to them.

In my work on the subject (e.g., this 2004 paper with SPC's Jared Guyer, and this 2006 paper), I've stuck with "cold core" as a loose way to refer to tornado activity near 500 mb closed lows where surface dew points may look deceptively small for tornadoes to occur. People can argue what's "near" and what's "not near" 500 mb closed lows (Jared and I used roughly 200 miles as a subjective but practical range for most of the cases we examined, including several "missed" tornado forecasts), and they can argue whether a particular case is a "true cold core case" (whatever that is). But I do think that misses the point. Significant tornadoes with surface dew points below 60 deg F are rather rare (in my database of 2001-2005 events, only 17 of 255 significant tornado occurred with a dew point below that!). The EF2 Hammon OK tornado occurred in an area where surface dew points were 52 deg F at best (see 3/8/10 surface map above), near the northwest edge/tip of the warm sector. It's clear that the associated cold air advection aloft (see -20 C 500 mb isotherm drawn over 3/8/10 surface map above) was a key component in generating the instability needed for that tornadic storm. So, if the "cold core" label does nothing more than serve as a flag or reminder for forecasters to at least consider the possibility for tornadoes within roughly 200 miles of closed upper lows when surface dew points appear "marginal" (e.g., upper 40s-low 50s F), avoiding a "surprise" when reports initially come in, then it has done it's job. If others want to do studies and papers to better define what a "true cold-core" tornado event is, I encourage that. But beware getting caught up in labels and definitions at the expense of practical meteorological assessment and experience.

Several people have asked me why the Hammon supercell appeared so much larger horizontally with more "typical" structure (e.g., large RFD etc., see Charles Edward's excellent photo above) than many low-topped supercells near 500 mb lows. It's important to note that the western Oklahoma late afternoon environment on 3/8/10 had plenty of clockwise curvature to the wind profiles, with 0-1 km storm-relative helicity (SRH) at least around 200 m2/s2 (not shown). Add to that around 1000 J/kg of surface-based CAPE (not shown), and the atmosphere doesn't care whether the storm has a "cold core" look to it (whatever that is). The shear/CAPE combinations were certainly large enough to support a significant tornadic supercell oer western OK in this situation. For what it is worth, cells occurring much closer to the midlevel low will tend to look "smaller", both vertically and horizontally, but there are certainly no hard and fast rules.

Why didn't the same system produce severe weather and tornadoes/funnels in the Kansas City area the next day? No one can say for sure, but there was almost a complete absence of sunlight with clouds surrounding both the surface and broadening/distancing midlevel low (see 3/9/10 satellite image above). This lack of heating for instability, along with with less focus and definition to both the surface and upper systems, might account for the lack of severe reports. There was one possible funnel report near Cameron MO, and the southern cloud base of a cell passing over my house north of Kansas City had some good motion in it. But the lack of sun and a well-defined dryline/clear slot kept Shawna and me from chasing that day. I will observe that, if "cold core" systems are tornadic near the 500 mb low on day 1, day 2 rarely results in tornadoes within roughly 200 miles of the midlevel low. This probably has to do with how difficult it is for such systems to maintain a favorable focus, juxtaposition, and organization near the midlevel low as they evolve over a couple days time.

Finally, several people have asked me why there weren't tornadoes in northern OK and southeast KS on Wednesday 3/10/10, (the Arkansas tornadoes after dark were deep in the warm sector away from the 500 mb low and Pacific front/dryline, in a good shear/CAPE environment with surface dew points around 60 F). Shawna and I chased that day (see my blog on 3/11/10), and noted several things seeming to go wrong as the day evolved. First, the surface moisture was having trouble returning, which resulted in initial warm advection storms at early afternoon being very high-based over southeast KS way out ahead of the surface low. Enhanced evaporative cooling below these high cloud bases generated outflow and westerly winds in the Coffeyville KS area (see 3/10/10 surface map above), where one would have otherwise expected a broad fetch of east or east-southeast winds spiraling into the northeastward-moving surface low over northern OK and then southern KS. This reduced SRH and low-level shear, retarded surface heating and surface moisture, and just generally "messed up" what might have been a well-organized "spiraling" surface pattern. This midlevel system was so strong that it still generated a photogenic arc of low-topped convection with sunshine behind it (see 3/10/10 satellite photo above) that moved into Chautauqua and Cowley counties of KS, producing several brief funnels from the cold air aloft and lots of pea-sized hail. But the outflow air from these cells (we measured 38 deg F!) seemed far too cold for supporting tornadoes.

As I mentioned in a talk at Denver a few weeks ago, there's much more that can go wrong than can go right with so-called "cold-core" systems and their ability to produce tornadoes. At best during spring or fall, maybe 1 in 10 will produce tornadoes within 200 miles of the midlevel low, and one often won't understand very well what's evolving in real time. I guess that's what makes these systems so interesting and such a challenge to forecast.

- Jon Davies 3/12/10

March 10, 2010 "cold core" chase near Sedan, KS

2010-03-11T11:25:00.000-08:00

I haven't had much luck chasing "cold core" setups (see this link) in recent years. My move to Missouri has tended to put me farther away from some of the more photogenic events in western Kansas and Nebraska, and I've also been reminded that there are many things can go wrong in trying to chase these type of events.

Yesterday's "cold core" event with a tight 500 mb closed low moving from central OK into southeast KS didn't produce any tornadoes -- the outflow air behind the cells we chased was 38 deg F (brrr!) according to our car thermometer! The tornadoes after dark (one deadly) in central Arkansas were deep in the warm sector well southeast of the upper low. But the "cluster" of cells that moved north-northeastward into Kansas west of Sedan (see arrow on satellite photo above), associated directly with the low aloft, was very photogenic. The late afternoon low-angle March sunlight brought out browns and blues (see 3rd pic above) very similar to my first "cold-core" chase near Pratt, Kansas on March 11, 1990 (ironically, 20 years ago today).

A few pics are posted above. The first is approaching the low-topped cell cluster near Sedan, KS, looking west-southwest along Highway 166. The second shows some brief funnels along the rain-free base looking southwest from west of Sedan. The third shows the gorgeous near-dusk lighting looking northeast as our cell of interest passes to the northwest of Sedan. The last shows another small cell developing to our east, and how the vertically-sheared updraft was stretched out horizontally, typical of early season low-topped convection associated with "cold-core" settings.

My wife Shawna posted some more of our pics with captions on Facebook, under Shawna Davies' photo album entitled "3/10/10 SE KS Cold Core album".

- Jon Davies 3/11/10

This week: 20 year anniversary of the Hesston tornado

2010-03-07T08:29:00.001-08:00

It was 20 years ago this week that an outbreak of tornadoes on March 13 1990, including the Hesston Kansas tornado, shook the central plains out of a several-year lull in significant tornado activity.

The Wichita Eagle has an excellent article by Stan Finger on the Hesston tornado at:
http://www.kansas.com/2010/03/07/1213543/1990-tornadoes-increased-awareness.html

Stan also has some photos and discussion on his blog at:
http://blogs.kansas.com/weather/

Later this week, I'll see if I can get some other review info about this event up on my web site. The Hesston tornado day was certainly one of the big turning points in my meteorological life.

- Jon Davies 3/7/10

"Cold Core" type setting produces dangerous snow squalls in Kansas City area on 2/14/10

2010-02-15T17:15:00.000-08:00

Just got back from ChaserCon in Denver -- great to meet and talk with many storm chasers there. Of course, while I was gone, a rather unusual weather event took place near home... Some convective snow squalls generated sudden white-out conditions in the KC area, causing trafffic accident pile ups at a couple locations on the Kansas side just after lunch on 2/14/10. Thankfully, no one was seriously injured. With as many as 40 cars piled up on I-70 near Bonner Springs (see KC Star photo above), it could have been much worse.

Believe it or not, these convective snow squalls were caused by an intense "cold-core" type closed low in midlevels moving southeast (see the NAM 500 mb analyses in 2nd graphic above). A strong vorticity maximum, or center of atmospheric "spin", was assciated with the midlevel low and moved right over the KC area around midday (see the "X" and red coloring on the NAM 500 mb maps above), providing a strong focus of forcing/lifting. A tight area of very cold temperatures just above the ground (-14 deg C, see the SPC 850 mb map at midday, 3rd graphic above) moved also across KC with this system. Combined with sun's heating (there was some sunshine just ahead of this system), low-level lapse rates increased rapidly (see orange area near Kansas City on the SPC 3-hr lapse rate change image, 3rd graphic above). All these ingredients working together generated a local area of CAPE and instability over the KC area (see RUC analysis sounding at KCI airport at 1:00 p.m. CST, 4th graphic above). Yes, there can be CAPE on days with surface temperature below freezing; this combined with the intense lifting/forcing system aloft undoubtedly contributed to the intensity and suddeness of the snow squalls.

The final graphic above shows a regional composite of radar reflectivity in low-levels around 12:00 pm and 1:00 pm as the "twisted" or curved area of snow squalls (see white arrow) associated with the vorticity center aloft approached the west side of Kansas City. The upper system was so intense and focused that an associated subtle trough in the surface wind field could be seen on the surface map at the same time moving southeast over the KC area (see blue dashed line on surface map in final graphic), even though the surface cold front was 400 miles to the south and east.

The Kansas City area National Weather Service at Pleasant Hill MO has posted a good page about this weather event setting at http://test.crh.noaa.gov/eax/?n=winter-0214201 0.

This event is a reminder that the contribution of low-level CAPE with some "cold core" midlevel lows to extreme weather isn't limited to just the warm season and thunderstorms!

- Jon Davies 2/15/10

ChaserCon talks, and 1/21/10 Huntsville tornado

2010-02-08T22:08:00.000-08:00

FWIW, I'll be in Denver this weekend to do a couple talks at Chaser Con. The first on Saturday 2/13 will focus on the June 7 2009 supercell (essentially non-tornadic) in NW Missouri that was followed by what seemed like thousands of storm chasers. The second on Sunday 2/14 will look at some short term chase targeting issues as well as some tornado forecasting stuff in somewhat potpourri fashion.

A couple talks I'm looking forward to are Erik Rasmussen's about what's left to learn about tornadoes, and Chris Novy's talk about chaser responsibility and safety. Chris in particular is smart, entertaining, and cutting edge, and his talk should not be missed by anyone who takes storm chasing seriously.

On another subject, Andy Fischer has written an excellent analysis of the recent 1/21/10 tornadic mini supercell setting at Huntsville AL (associated with a "cold core" midlevel low). In this case, the tornado occurred with a cell well south of the surface low along the trailing front, which is somewhat different than the "typical" cold core setup. Andy's post is on his blog at: http://tornadoheadblog.blogspot.com

Hope to talk with some storm chaser colleagues in Denver!

- Jon Davies 2/7/10

Tornado setting in Los Angeles area 1/19/10

2010-01-20T12:07:00.000-08:00

I haven't done a case study for awhile... Before today's tornadoes (Jan. 20) in Texas and Louisiana, it's been a quiet winter regarding severe weather in the southern states. But yesterday's little tornado episode on Jan. 19 (see 1st graphic above, a capture from video at Sunset Beach CA) near Los Angeles caught my eye, with some minor damage in the Huntington Beach area. Fortunately, the tornadoes/waterspouts around 2100 UTC (1 p.m. PST) were weak, as most California tornadoes are.

The 500 mb WRF model analysis showed a strong short wave of energy aloft with an intense vorticity max (atmospheric forcing and "spin") crossing southern California yesterday afternoon (see "X" and "orange" vorticity area on 2nd graphic above). At the surface (3rd graphic above), a small low pressure area (mesolow) was approaching the Los Angeles area from the southwest before 2100 UTC with an east-west boundary along the coast just south of L.A. (Huntington Beach is located by the black square in the same graphic). Dew points were in the low 50's F south of this boundary, and the tornado activity seemed to be focused along it where low-level shear and vorticity ("spin") were probably concentrated.

On radar from Santa Ana/SOX (4th graphic above), a "circular" pattern of small cells with red reflectivity was visible over the ocean to the southwest of the L.A. basin around 2000 UTC, moving northeastward (see black motion arrow in same graphic). This pattern of cells was associated with the mesolow mentioned above, and came onshore producing waterspouts and at least one tornado between 2030 UTC and 2100 UTC in the Huntington Beach area (black square in same graphic).

A modified RUC model sounding for 2100 UTC at Santa Ana (see last graphic above; just east/northeast of Huntington Beach) suggested that instability/CAPE was certainly not large (only around 200 J/kg). But the available CAPE was located extremely close to the ground, probably inducing strong stretching for storm updrafts in low-levels near the surface focus of the mesolow and boundary. In addition to CAPE, the wind profile on the same graphic suggested large low-level shear (storm-relative helicity, SRH > 300 m2/s2) available for tilting and stretching contributing to tornado formation near the focusing boundary.

In many ways, even without a closed 500mb low aloft, this setting has some common features with "cold-core" tornado settings in spring and fall in the Plains (e.g., strong forcing and sharp vorticity max aloft, surface low and boundary extending east of the low, surface dew points only low 50's F, but CAPE located very close to the ground). In fact, most California tornado settings, whether in the L.A. area or farther northward in the central valley of California, are some variation on this type of setting, with total CAPE often less than 500-1000 J/kg.

- Jon Davies 1/20/10

Update: 2/19/10 (1 month later) - L.A. area storm chaser Will Wilkens has called to my attention that photos from this tornadic event that I originaly posted here (and have now deleted) were "phonies". One was from the 5/22/08 Riverside CA landspout event, and another was a generic waterspout image. I've replaced those with a video capture above of the real tornado that Will pointed me to (Thanks!). I'll have to be more careful in the future... Various websites of TV or news viewer photos are increasingly posting stuff that's labeled wrong these days just to appear current, it seems. Thanks for the information, Will.

Final thoughts for 2009

2009-12-31T08:13:00.000-08:00

I haven't been much into blog posting or blog reading lately. That's expecially true for me about storm chasing, which seems to have evolved into a largely clickish, competitive, petty, and fame-seeking "activity" recently. Where has the wonder of nature aspect gone? Where is the true interest in learning how nature and weather works?

As people who know me understand, I've always been interested in severe weather forecasting research. But now I'm even a little down on that, too. I don't see forecasting and warnings getting significantly better in the near future with the data density and observational equipment we have currently available, and the increased reliance on computer models. Honestly, warnings for big weather events are already pretty good. All the talk about in TV storm chasing shows about saving lives with more weather research seems moot and more than a little silly when people don't respond to warnings, or even seem to hear them through all the noise of our 24/7 media these days.

Events with excellent warnings like Hurricanes Katrina and Ike (Tim Marshall gave an excellent November talk in KC about Ike and how poorly many people in the Galveston area reacted to the intensely-worded warnings), and the Super Tuesday tornado outbreak in 2008, underline that saving lives these days in extreme weather events is more a sociological issue (getting people to hear and respond) than a meteorological one. These thoughts aren't new or ground-breaking, and are certainly being recognized and studied in programs like UCAR's WAS*IS (see http://www.sip.ucar.edu/wasis), which is a good thing to see.

Anyway, I feel that I'm in transition with my focus and goals at this point in my life, and it will be
interesting to see where that leads in 2010.

- Jon Davies 12/31/09

Jon to serve as Associate Editor for Weather & Forecasting

2009-11-24T09:29:00.000-08:00

I've been asked to be an Associate Editor for the AMS journal Weather & Forecasting (WAF) in 2010. I'll be reviewing papers in a more "official" capacity than in the past (I reviewed 3 papers for WAF in 2009), and I appreciate editor Bill Gallus asking me to serve.

In other news (it's been a busy month for me, so no new case studies to post), I've been asked to speak again at the National Storm Chaser Convention (now known as ChaserCon) Feb, 12-14, 2010. I've been taking time off from talks lately, but Shawna and I always enjoy the Chaser Convention, and are looking forward to going this year. Roger Hill and Tim Samaras always do a great job putting ChaserCon together, which is not an easy job!

Finally, I've had a few people ask me when Tornado Road will be shown again. All 6 episodes of the show will be re-aired on The Weather Channel on Thanksgiving evening 11/26/09. FWIW, Shawna and I are in episodes 1 and 2 (6:00pm-8:00pm), and episodes 4 and 5 (9:00pm-11:00pm).

- Jon Davies 11/24/09

Comments about "Tornado Road" on TWC

2009-10-25T09:35:00.000-07:00

I've finally had a chance to watch all 6 episodes of Tornado Road on TWC, and felt I should post a few comments.

Some people are saying that the show was somewhat repetitive, depicting chasers driving in lots of rain cores (there were many HP storms during filming) and waiting for things to happen. But, in many respects, that's what real chasing is about. The show was intended to be, in a way, like "Deadliest Catch" to show what typical storm chasers (like crab fishermen) go through during a typical season. In that sense, I think the show succeeds.

However, I was very disappointed that extensive interviews filmed with NWS Omaha personel such as Daniel Neitfeld and Brian Smith regarding the June 11 '08 Boy Scout camp tornado were discarded. I want to emphasize that the NWS did a great job with warnings that day, and also with the ground survey. My work was informal and only supplemental to their work, but that wasn't shown or clarified. I very much wanted to see the NWS material included in the program. But on "reality" shows like this, unfortunately, one has no control of the editing and what will and won't be shown.

We also allowed a camera crew to film Shawna and me in a short "storm chase" wedding with friends in the Flint Hills in late June '08. Just to be clear, we chose a garden-variety thunderstorm day with minimal threats. Please rest assured that Shawna and I would never make light of a severe weather situation with potential to hurt or injure people.

All that said, Shawna and I enjoyed taking part in the show, and the production crew from Original Productions was fantastic and fun to work with.

- Jon Davies 10/25/09

"Tornado Road" air times on The Weather Channel

2009-10-15T21:43:00.000-07:00

The Weather Channel has confirmed (finally) through a press release and on-air/online advertising that the short series "Tornado Road" will indeed air beginning Sunday October 18. The first three episodes (Shawna and me included) will be at 7 pm, 8 pm, and 9 pm CDT (see EDT listings here).

Additional air dates through October 30 (these are tentative!) are listed below:
Times EDT, not CDT !

October 18
TR1 8p and 2a
TR2 9p and 3a
TR3 10p

October 19
TR1 2p
TR2 3p

October 20
TR3 2p
TR4 3p

October 21
TR5 2p
TR6 3p

October 24
TR1 8p
TR2 9p and 2a
TR3 10p and 3a

October 26
TR1 3p

October 27
TR2 3p

October 28
TR3 3p

October 29
TR4 3p

October 30
TR5 3p

I'm sure we'll all be portrayed as "thrill seekers" (oh boy), but if you choose to watch, Enjoy!

- Jon Davies 10/16/09

Paper in Weather & Forecasting August 2009

2009-09-20T15:34:00.000-07:00

FWIW, a "Reply" paper (in full PDF form here) I wrote in response to comments by Roger Edwards and Rich Thompson was published in the latest issue of Weather & Forecasting journal (Aug 2009). The case study concerns a violent tornado (see photos above) in North Dakota on July 18, 2004, with the original paper published here in 2007.

The discussion focuses on mixed-layer LCL heights that appeared "relatively high" for a violent tornado, near 1500 m AGL, compared to means and medians that were 900-1000 m AGL from a database of RUC soundings 2001-2008 that I put together associated with violent tornadoes (F4-F5 or EF4-EF5). What's "relatively high" and what isn't is pretty subjective, but the North Dakota case did fall at the far upper end of MLLCL height distributions I've seen for violent tornadoes, and I felt the case was worth documenting. Forecast-wise, given CAPE-shear combinations that appear supportive of supercell tornadoes over a fairly large area, it's sometimes easy to get focused on areas where the MLLCL heights are lower, say less than 1000-1200 m. The North Dakota case examined and others, such as 7/11/08 in west central Minnesota, are a reminder to keep and eye on areas farther west and southwest where MLLCL heights on the SPC mesoanalysis (see graphic above) appear to push values at the upper end of published tornadic database distributions (e.g., near 1600-1800 m AGL).

Researcher Dr. Paul Markowski recently suggested to me by e-mail that such MLLCL heights aren't really that "high", which may be true. Certainly, when MLLCL heights get up above 2000 m AGL, that appears prohibitive for strong or violent tornadoes due to subcloud mixing and the potential for evaporative cooling and cold pooling in low levels. Going back to Dr. Markowski's 2002 paper (here) about rear-flank downdraft observations, he suggests that, statistically, the spread between surface temperature and dewpoint may be a more reliable limiting factor than LCL height when assessing potential for supercell tornadoes. This is because we have denser and more reliable surface observations, while model-based mixed-layer parcel lifted computations (e.g., from the RUC, which includes "ML" products from the SPC mesoanalysis) are highly affected by model forecast moisture depth and accuracy issues.

Although not in the August 2009 paper, observed surface temperature and dew point spreads from my 2001-2008 tornado environment database suggest that spreads of 5-15 degrees F appear most optimum for strong or violent tornadoes, which agrees with Dr. Markowski's observational field work from VORTEX1. When those spreads get near 20 degrees F and higher, that's when support for stronger supercell tornadoes seems to really break down. But please don't use that as a hard and fast "threshold", because nature doesn't recognize "thresholds"! FYI, the North Dakota violent tornado case in my "Reply" paper had temperature to dew point spreads that were around 18 degrees F.

- Jon Davies 9/20/09

Surprise tornado in Minneapolis on Wednesday 8/19/09!

2009-08-22T10:19:00.000-07:00

People close to me know that I love studying "surprise" situations that are very difficult as forecasts. Wednesday's tornado near downtown Minneapolis around 2 p.m. (see photos above) was indeed a surprise, as the area was socked in by clouds, and the small cell that produced the tornado was embedded in a larger complex of rain (see 2nd graphic above) where total CAPE appeared small. There were no watches or warnings prior to the tornado. At first glance, it appears that the small tornadic supercell was an odd random incident. But, though difficult if not impossible to forecast, a closer look reveals some clues that point to why the tornado occurred in the area where it did. These might help to heighten short-term situational awareness in future situations of a similar nature.

The 3rd graphic above shows the midday surface map, with a small low and convergence focus visible in the wind flow fields near Minneapolis. The low appeared to be right at the intersection of some subtle wind shift boundaries, organized not unlike the surface pattern in some cold core events, although this setup was not associated directly with a 500 mb cold core low. Instead, a sharp negatively-tilted 500 and 700 mb trough (see SPC mesoanalysis, 4th graphic above) was moving northeast across southern Minnesota, with a comma cloud and vorticity center visible with the wave moving northeast in satellite imagery (see the inset enhanced IR image on the surface map graphic). This vorticity center was trackable from near Omaha after daybreak to the Minneapolis area at early afternoon, with the comma cloud expanding and becoming better defined in the enhanced satellite imagery. The surface low and boundaries over Minnesota were organizing ahead of and in response to this upper feature and forcing, even within the large complex of rain and embedded thunderstorms.

Going back to the radar image (2nd graphic), if one looks closely, there was a pattern to the precipitation echoes, with a flat "S" shape (indicated by heavy white dashed line) formed by the stronger reflectivity returns corresponding to the N-S boundary roughed in on the surface map. The surface low position was likely located near the middle of this "S" (marked by a red "L" in the radar image), and the small tornadic supercell was located immediately east or northeast of this focus where increased shear and convergence would be expected, consistent with the surface analysis (3rd graphic). The SPC mesoanalysis graphics (4th graphic) also suggested increased 0-1 km storm-relative helicity (SRH) pointing into the area from the southeast, with maximized low-level CAPE in the Minneapolis-St. Paul area, even within the large convective complex.

The RUC analysis sounding at MSP (Minneapolis International Airport, southeast of downtown) at about the time of the tornado also suggests that large low-level shear and SRH were present (see hoodograph on last graphic above). The same sounding confirms that large low-level CAPE bunched close to the ground was present in a nearly saturated environment (little or no mixing for near-surface air parcels), even though total CAPE was small (at best, around 400 J/kg). This vertical arrangement of CAPE and SRH co-located in low-levels probably helped to optimize tilting and stretching of horizontal low-level vorticity near the boundaries and surface low focus to generate the tornado.

Thankfully, with the marginal total CAPE, nothing more than a weak tornado (EF-0) could get going, but not without leaving a south to north trail of damage across south Minneapolis to near the downtown. A later tornado east-southeast of Minneapolis near Cottage Grove (not shown) was rated EF-1, and occurred with a cell on the bulging boundary south and southeast of Minneapolis as it "curled" and "wrapped" northeastward during the next 45 minutes in response to the evolving wave and energy passing aloft.

This case suggests that evolving and expanding comma clouds in IR imagery indicative of a strong vorticity center and wave aloft be watched carefully as they move northeastward. Even with rain and only small total CAPE, if there is focused surface congergence (e.g., a mesolow with boundaries) in response to the wave and vorticity aloft, and at least some CAPE (e.g. 300-500 J/kg low in the vertical profile with little or no CIN), look out! A surprise may be in store with that energy focusing into a relatively small area.

Additional information and graphics for this event are on the NWS Minneapolis web site here.

- Jon Davies 8/22/09

Updated material on 700 mb temperatures and estimating the "cap"

2009-08-17T10:35:00.000-07:00

I put together a new case study (10 July 2009) showing how 700 mb temperatures can be helpful in estimating the location of an inhibiting capping inversion:
10 July 2009 "cap" case study in the central plains

I've also updated my original material that is an informal reference about using 700 mb temperatures as a first guess estimate of the "cap":
Using 700 mb temperatures as an estimation of the "cap" in the central plains

There are several caveats given, including the fact that the 700 mb temperature values often don't work well in the High Plains and westward due to surface heating over elevated terrain in the warm season, and also upslope situations. Although only a very rough guide, the table and information with this material can be useful in raising awareness about possible "cap busts" when forecasting. Hope some find these useful.

- Jon Davies 8/17/09

A surprise tornado in a very subtle setting - northeast Kansas on July 28, 2009.

2009-08-02T15:59:00.000-07:00

Weak tornadoes probably occur more often than we think. If there's no one to see a tornado and it doesn't hit anything over open country, it doesn't get reported. A weak, brief, but interesting tornado was photographed in northeast Kansas near Centralia KS last Tuesday 7/28/09. The Topeka NWS office has a story about it on their web page here.

Veteran storm chaser Doug Nelson of Seneca KS happened to notice the tornado form from a rapidly rotating cloud base under a developing "shower" southwest of his shop at Centralia, and took the photos above around 1:20 pm CDT (1820 UTC). The tornado was brief and probably wouldn't have been noticed if not for Doug's observations.

In and of itself, this tornado isn't important... it was weak and no damage reported. But such tornadoes in subtle settings can help meteorologists study and become aware of ingredients that, when more pronounced, might lead to other more significant tornadoes in atypical settings.

Above, the first of two low-level radar base reflectivity images (about 1830 UTC) showed a subtle boundary as a hard-to-see ragged "fine line" oriented WSW to ENE (indicated by dashed white line). The tornado occurred with a small unimpressive echo (indicated by the white arrow) on this boundary. In the 2nd radar image above, the boundary was more evident as a line of storms fired along it, but this was well after the tornado occurred. Even at 1845 UTC on satellite (3rd graphic above), it was hard to see either the boundary or the "shower" (arrow), although local clearing was evident behind the morning storms over Missouri and extreme northeast Kansas, providing a little heat and air mass recovery.

The boundary was also hard to pick out on the 18 UTC surface map (see heavy dashed line on 4th graphic above), apart from the ESE wind at Manhattan KS and southwest wind at St. Joseph, with winds northerly at stations to the north. But, in fact, the boundary was probably a weak cool front moving slowly southeastward under an unseasonably deep trough at 500 mb (shown in the same graphic), obscured by the morning clusters of storms and outflows well in advance.

The NAM/WRF analysis sounding at Holton KS, located north of Topeka and southeast of Centralia KS, is shown in the last graphic above. This local environment estimate showed not a lot of CAPE (400-500 J/kg), but notice that a well defined "fat" area of CAPE was evident between 700 and 600 mb (about 3.5 km above ground). With this CAPE low to the ground (typical spring/summer thunderstorm soundings have the "fattest" CAPE much higher, around 6-7 km above ground), this suggests potential for rapid acceleration of air parcels in developing local updrafts, resulting in strong stretching. With the boundary, vertical CAPE distribution, and the shower right over the boundary with stretching, those ingredients are what probably came together as a local "mesoscale accident" to spin up a brief surprise tornado. Certainly not an event that could be forecast or even nowcast... a very subtle setting.

Nature never ceases to surprise!

- Jon Davies 8/3/09

Waterspout and separate tornado near Daytona Beach on 7/24/09 - a similar setting to some landspouts setups in the Plains?

2009-07-26T11:03:00.000-07:00

Friday 7/24/09 saw a photogenic waterspout in Florida off Ormond Beach (see 1st photo above) just north of Daytona Beach, followed by a tornado inland at Port Orange (see 2nd photo above, south of Daytona Beach) that damaged or destroyed many manufactured homes. The setting for Friday's waterspout and tornado appeared similar in some respects to some landspout tornado settings in the Plains.

The second set of graphics above shows lowest elevation angle radar reflectivity images from around 2100 UTC to 2230 UTC on Friday, with some key features labeled. The white dashed line and arrows in the first 2 images indicate the position of a sea breeze boundary inland over eastern Florida, seen by a fine line on Melbourne's radar. Notice how the sea breeze boundary extended back out over the Atlantic near Daytona Beach (DAB) at 2106 UTC, with thunderstorms having formed in a separate convergence zone to the northwest of DAB. By 2141 UTC, these storms had moved east and encountered/converged with the sea breeze boundary near DAB. At this time the waterspout was in progress off Ormand Beach (OMN) and lasted until around 2155 UTC. It moved slightly onshore at one point and did minor damage as a tornado. By 2230 UTC, the storms had back built along the boundary onshore to the south and southwest of DAB. Around 2220 UTC to 2230 UTC, a tornado developed inland over Port Orange, and did the aformentioned damage to many homes.

The boundary seen on radar (and also satellite, see 3rd graphic above) was of critical importance in generating the waterspout and later tornado. It is common knowledge that most waterspouts in Florida occur along land/sea breeze boundaries. What made this case interesting was that a tornado eventually formed inland from the same boundary, similar to how some non-supercell landspout tornadoes develop southwestward along stationary northeast-southwest boundaries in the Plains. A paper by Caruso and Davies discusses some of these Plains settings.

In addition to the boundary, SPC mesoanalysis graphics (last set of graphics above) from 2100 UTC on 7/24/09 indicated some environment characteristics that were somewhat similar to the Plains settings mentioned above. Low-level lapse rates (0-3 km) were steep and maximized just southwest of DAB (heavy black dot in the graphics), and 0-3 km CAPE was maximized as well. The combination of these ingredients with a stationary or slow-moving boundary over which thunderstorms are developing can increase stretching in updrafts to create non-supercell tornadoes using vertical vorticity along the boundary. Although the setting and orientation of the boundary did have some similarities to Plains landspout settings, it should be emphasized that such storms in the Plains are typically much higher based, and the low-level lapse rates tend to be much steeper (around 9 deg C per km) due to the higher elevation. Florida tornado settings don't require such steep lapse rates, low-level environments are much more moist, and land/sea breeze fronts provide plentiful boundaries.

WInds at 500 mb (see last SPC graphic above) were only around 20-25 kts over northeast Florida on Friday, so while one or two of the storms along the boundary may have had some brief/marginal supercell characteristics, it appears that the primary contributors to the waterspout and separate tornado were non-supercell/non-mesocyclone processes along the boundary.

- Jon Davies 7/26/09

New papers about nighttime tornadoes by Davies & Fischer

2009-07-12T21:28:00.000-07:00

Two new peer-reviewed papers about nighttime tornado environments written by Andy Fischer (AWC in Kansas City) and me have just been published online in National Weather Association Electronic Journal of Operation Meteorology (NWA EJOM):

Environmental Characteristics Associated with Nighttime Tornadoes
By: Jonathan M. Davies and Anthony Fischer

Significant Nighttime Tornadoes in the Plains Associated with Relatively Stable Low-Level Conditions
By: Anthony Fischer and Jonathan M. Davies

There's some interesting things we found with nighttime tornado environments, including much larger storm-relative helicity (SRH), and significant differences in CAPE and CIN between the Plains and the southeastern United States. In the second paper, we looked specifically at a couple of significant nighttime tornado events in Kansas in 2008 that were associated with unusually large CIN and low-level stability.

I hope that meteorologists and students find these useful!

- Jon Davies 7-12-09

"Surprise" supercells & tornadoes in Kansas on 6/20/09

2009-06-21T10:00:00.000-07:00

Severe weather events the past couple weeks have incuded a highly visible tornado along the Palmer Divide in Colorado, and strong tornadoes near Macksville KS, Aurora NE, and Austin MN. Tornadoes in Kansas yesterday (5-10 reports on Saturday 6/20/09) weren't anywhere near as strong, but were more of a surprise within a subtle and somewhat unusual environment. Pics above from a supercell in Franklin County of eastern Kansas show one of the brief tornadoes, courtesy Rick Schmidt and Randy Cooper.

The surface map (2nd graphic above) at late afternoon confirmed an east-west warm front moving north through Kansas, with easterly winds and dew points in the 70s F. The RUC model at 500mb (3rd graphic above) showed upper energy in the form of a wind max moving across Kansas from the southwest, and CAPE-SRH combinations (EHI) and CAPE in low-levels (also in 3rd graphic above) forecast to be maximized across central and eastern Kansas. For any thunderstorms forming along and north of the front, this suggests that supercells were possible, and maybe some tornadoes. Radar above (4th graphic above) shows storms shortly after 7 p.m. CDT over Kansas, with arrows indicating tornadic storms at that time (the complex near Hutchinson KS became tornadic later).

The RUC analysis sounding over eastern Kansas at Topeka at 7 p.m. CDT (last graphic above) matched the observed Topeka RAOB very well. To my mind, the most interesting feature was the area of fattest CAPE located at 600 mb (about 4 km or 13,000 ft above ground). Compare that with the RUC analysis associated with the Aurora NE tornado (also shown in last graphic above), where wind shear/SRH and total CAPE were much larger, but the fattest area of CAPE was located much higher (near 300 mb, or roughly 9 km/30,000 ft above ground). On the Topeka profile from yesterday, the fattest area of CAPE was at least _3 miles_ lower in the vertical than in Wednesday's Nebraska tornado environment. Although Saturday's storms weren't anywhere near as strong or severe, they produced a number of tornadoes (9 reports on the SPC log). The fat area of CAPE near 600 mb (relatively low in the profile, associated with cold air at that level) was evident on RUC profiles across much of Kansas, and was probably a notable contributor to the number of weak tornado and funnel reports from western to central and eastern Kansas on 6/20/09. What probably happens in such settings is that "fat" CAPE closer to the ground produces more rapid upward accelerations in updrafts, translating to more vertical stretching which can cause tornadoes and funnels, even in a weaker shear environment, not unlike many tornado events associated with 500 mb cold core lows. The lack of large SRH and low-level shear on Saturday (compare the wind profiles on the 2 soundings shown above) probably kept Saturday's tornadoes brief and weak.

Sorry about no posts lately... been busy with non-weather stuff,

- Jon Davies 6/21/09

Kirksville, MO tornado environment on 5/13/09

2009-05-18T14:16:00.000-07:00

Sorry I haven't had time to post any case studies for awhile. But with 3 deaths from tornadoes in northern Missouri last Wedensday 5/13/09, I decided to make time for a short analysis of that event.

The tornadoes were rain-wrapped at times (see the photos above), and the most intense damage was rated EF-2 by the National Weather Service. A good environment for generating significant tornadoes aided the supercell that produced the 3 tornadoes in sequence from near Milan to Kirksville.

The surface map at late afternoon showed a low (see surface map above) moving eastward across northern Missouri, with south-southeast winds just east of the low and a retreating outflow boundary from morning storms that had moved across the area. Farther southwest, surface winds had a westerly component. Storms on radar began to build at mid afternoon near the low and then southwestward in advance of a surface front. But the tornadic storm (see arrow on radar images above) remained near a focal point just east of the surface low, and could take advantage of southeasterly low-level flow and increased storm-relative helicity (SRH).

RUC model analysis soundings at Chillicothe (CDJ) and Kirksville (IRK) highlighted the dramatic difference in low-level shear (see the sounding plots above). At CDJ, although MLCAPE was quite large (near 3000 J/kg) and deep layer shear was favorable for supercells (around 40 kts), southwest winds made for a small/straight/unidirectional hodograph in low-levels with small SRH. In contrast, at IRK east of the surface low and outflow boundary, low-level wind shear was quite large as a result of southeast surface winds and stronger flow just above ground, with a looping hodograph and big SRH (>400 m2/s2!). Even though MLCAPE was less than 2/3rds that on the CDJ model sounding, the combination of very strong low-level shear and strong deep layer (> 50 kts) in the Kirksville area really made a difference!

Saddled with an important mid-afternoon meeting, Shawna and I were only able to make it to a supercell east-northeast of Chillicothe (see the cell southwest of the Kirksville supercell near CDJ on the 5:02 pm radar image above), which was frustrating. Although the Chillicothe storm had a lowering and some decent supercell structure, the roughly 50 mile distance between supercell locations certainly made for distinctively different storms and tornado potential.

- Jon Davies 5/18/09

Talk for Kansas City AMS chapter Thurs., April 30

2009-04-30T10:34:00.001-07:00

Been really busy lately, so no posts or cases studies in the past couple weeks. If I get time, I'll see if I can do a post and quick study of the setting that spawned the tornado just west of Kansas City last Saturday (April 25), so stay tuned. Of course, I was in Oklahoma on my 2nd storm chase of the season that day. Ouch.

I'll be doing a talk this evening, "Busts, Thrills, and Things Learned from Storm Chasing" for the Kansas City AMS chapter at Cupini's restaurant in Westport around 7:30 p.m. Looking forward to seeing some fellow meteorologists and storm enthusiasts there.

- Jon Davies 4/30/09

Prolific cold core tornado event in southwest KS on 4/18/09

2009-04-19T09:47:00.000-07:00

Shawna and I have had quite a lot of difficult family stuff going on, so I haven't posted lately. But it has certainly been an early spring season of midlevel cut-off lows and cold core systems so far, most of which have failed to produce tornadoes.

For example, way back on 2/9/09, a large dynamic cold core system raced northeast through the plains, but overwhelmed any semblance of a surface pattern that might support tornadoes due to a dry slot that blasted northeast at 70 mph, a typical problem with very early season cold core systems. Then in early April, a fairly organized system on 4/4/09 lifted through Nebraska, but could only produce brief gustnado-like vortices with storms because of dew points only in the 40's F and rather high cloud bases (usually not supportive of cold core system tornadoes). A few days later on 4/9/09, a strong cold core system in northern Oklahoma and Kansas again was "too dynamic" when the surface low jumped and reformed farther east, destroying the surface pattern focus beneath and near the midlevel low. The resulting large area of convection that developed tended to overwhelm the surface pattern and effective boundary intersections that are often important for tornadic cells in cold core cases, though there were strong tornadoes later that night in Arkansas and Louisiana within the broader warm sector farther to the southeast.

Yesterday (Saturday 4/18/09) finally saw a cold core system that produced several tornadoes over a 90 minute period that were well photographed in southwest Kansas, northwest of Dodge City (see photos above). There was some damage east of the tiny town of Kalvesta, but thankfully no injuries. Being that this was a slow-moving system that was not overly "dynamic", surface features were able to focus near Dodge City, and an initial storm that developed was able to stay isolated for a long period near the midlevel low and cold air aloft and the surface boundary intersection, rather than being overwhelmed by a large area of convection.

I watched this event develop from Kansas City (I really miss living in central KS!), and noticed the surface pattern at late morning was focusing over southwest Kansas (see 2nd graphic above) near a surface low and boundary intersection west and south of Dodge City. The 500 mb closed low aloft was not far to the west-northwest, near the Colorado border (see positions marked on satellite image, 3rd image above), with plenty of cold air aloft and temperatures near -20 C at 500 mb, and -5 C at 700 mb. (See here for more on cold core tornado settings.) Put that cold air above surface dew points around 50 F advecting northwestward into the high plains, and you have a recipe for strong stretching in isolated storm updrafts below 10,000 ft or 3 km. The tight spin/vorticity/forcing of the nearby midlevel low probably helped as well.

Surface convergence at 1:00 p.m. CDT (see 18 UTC SPC maps, 4th graphic above) was maximized near the surface low and dryline/warm front intersection near Dodge City, Surface-based CAPE was also plentiful for a cold core setting (> 1000 J/kg, see SPC map). The supercell developed rapidly between Dodge City and Garden City between 12:30 p.m. and 1:00 p.m. CDT (not shown), and the first tornado developed barely 20 minutes into the storm's lifetime. Such rapid tornado development relative to storm initiation is not uncommon with cold core settings, probably due to the majority of CAPE being located below 500 mb (relatively close to the ground, see the final graphic above, a RUC analysis/estimation at Dodge City during the tornadoes).

It is interesting to note from the RUC profile above that there was very little if any low-level shear (storm-relative helicity or SRH) in the local environment, reiterating the fact that cold core tornado events near the midlevel low don't always require lots of helicity. Limited low-level shear and the surface focus near a reasonably well-defined boundary intersection seemed to suffice in this case.

- Jon Davies 4/19/09

Unexpected tornadoes in North Carolina on 3/27/09, while snowstorm raged in the Plains

2009-03-29T12:20:00.000-07:00

It was a wild week of weather across the country, with flooding in North Dakota and a blizzard in Kansas (the town of Pratt where I grew up got 28 inches of snow!). Early in the week, there were tornadoes and injuries in Nebraska on Monday 3/23/09, and tornadoes again in Mississippi early Thursday morning with 20 injuries and many homes destroyed in the town of Magee. However, the event that really caught my attention was the tornadoes in North Carolina on Friday 3/27/09. It was unexpected (no severe outlook, watches, or even warnings early on), and involved several tornado reports over a 2 hour period with one tornado rated EF2 on the south and east side of Fayetteville, North Carolina (see photos above).

Unexpected events are always useful to look at to see if there are clues from which we can learn as forecasters. Looking back at Friday's case, there was a strong short wave and wind max aloft forecast to eject northeastward across the Carolinas (see 700 mb forecast map above), out ahead of the large blizzard-producing trough over the central plains. At the surface, there was a significant axis of dew points pointing northward into the Carolinas ahead of the shortwave (see circled area on the SPC dew point analysis, 3rd image above, at early to mid afternoon). On the same map, I've drawn in the estimated position of the freezing line at 700 mb. Notice how this colder air aloft was overlying the dew point axis over North Carolina. This would likely contribute to more significant instability in that area than one might detect on available total CAPE analyses (only around 250 J/kg, not shown).

In the 4th image above, I've drawn in the surface front on the 20 UTC SPC surface wind and pressure analysis, and also included the 20 UTC 850 mb map and 20 UTC analysis of estimated low-level CAPE below 3 km AGL. Notice how there was a low-level jet of 30-40 kts at 850 mb overrunning the surface front over northern South Carolina and southeast Nouth Carolina, ahead of the short wave aloft. This would provide lift and focus for storms near the warm front/stationary front, and probably increase the wind shear. The low-level CAPE map also indicates that there was a maximum of CAPE close to the ground in this same area, suggesting significant CAPE that might be missed when looking at relatively small values on corresponding total CAPE analyses.

The last image above shows a small supercell storm (see arrow) approaching Fayetteville (FAY) on radar at 2024 UTC and 2057 UTC, and a NAM/WRF model forecast profile for Fayetteville near the same time. Notice how the CAPE on the profile was bunched down low, with the fattest CAPE located near 700 mb (3 km above ground). A more typical tornado sounding in the Plains associated with supercells would have the CAPE distributed through a much deeper layer, with the fattest CAPE area located up around 400 mb (near 6-7 km above ground), more than twice as high as the 3/27/09 Fayetteville profile. Even though the low-level shear and storm-relative helicity (SRH) on this profile were not impressive (< 100 m2/s2, a value reinforced by RUC model profiles and SPC estimates, not shown), the rapid upward acceleration of updraft parcels due to CAPE residing so close to the ground may have facilitated tilting and stretching of the available low-level SRH near and north of the front. This could be a key issue regarding tornado potential in this case that involved tornadoes from very low-topped supercells.

Events and settings like this appear to reinforce the importance of detecting areas where CAPE is located atypically low in the atmosphere. This is particularly true when total CAPE looks marginal (say, < 500 J/kg), yet there are other favorable features present such as a short wave aloft, surface boundary, and surface dew point axis in place. Thankfully, tornadoes in most such events are not that strong (usually EF2 or less in intensity).

- Jon Davies 3/29/09

9th Annual Severe Symposium in Lawrence KS, and Storm Chasing Series Shelved

2009-03-19T09:43:00.000-07:00

Shawna and I will both be speaking at the 9th Annual Severe Weather Symposium in Lawrence, Kansas this Saturday 3/21/09. The Symposium will be held from 7:30a - 1:00p at the Lawrence Arts Center, 940 New Hampshire St. in Lawrence. Here's the web site.

Shawna's talk will be about how storm chasers can help with first response, and also educate those in their local communities about severe weather awareness. I'll be doing a talk about the tornadoes in Kansas and Iowa on June 11, 2008.

Some other news... The storm chasing series that was to be broadcast this spring has apparently been shelved or cancelled by network executives. Shawna and I were to be in a couple episodes, but it now looks like it won't be aired. Such is the uncertainty of TV :-(.

Hope to see some people at the Symposium on Saturday.

- Jon Davies 3/19/09

Storm chasers featured on The Weather Channel's web site

2009-02-17T21:10:00.000-08:00

FWIW, I'm being featured currently on The Weather Channel's web site along with several other prominent storm chasers. See:

http://www.weather.com/tv/programs/Storm-Chasers.html

There's some photos, video, and miscellaneous information about me there. Thanks to Tony Grohovsky at TWC for setting this up.

Shawna and I just got back from the Denver Chaser Convention. It was great talking with so many chasers there, including Reed Timmer, Tim Samaras, Roger Hill, Mike Umscheid, Matt Crowther and Betsy Abrams, Jim Leonard, Tony Laubach, Brandon Ivey, Kory Hartman and Kenny Allen, and I could on and on. The presentations by experts such as Rich Thompson, Dr. Greg Forbes, Tim Marshall and others were excellent. And Shawna's talk about chaser preparedness and first response was very well received.

Here's a good recap of the convention at examiner.com:

http://www.examiner.com/x-219-Denver-Weather-Examiner~topic86015-weather-events

- Jon Davies 2/17/09

Deadly tornado after dark in south-central Oklahoma on 2/11/09

2009-02-11T07:56:00.000-08:00

Sadly, 2009's first "tornado disaster" has come with a tornado after dark at Lone Grove (near Ardmore) in south central Oklahoma. With news reports of at least 8 dead, one has to wonder if darkness contributed to the death toll. In 2007, 2008, and now 2009, we continue to see damaging and deadly nighttime tornadoes in the Plains, something more commonly associated with the southeastern United States.

Above, two radar reflectivity images (see white arrows) show the deadly supercell at 0000 UTC, and again at 0135 UTC, just after the time the tornado was hitting Lone Grove. With a large line of storms to the west and north, this reaffirms that discrete supercells tend to produce the strongest tornadoes, removed from immediate interference by adjacent storms. As the line to the west overtook and engulfed the supercell after 0200 UTC, tornadoes ceased.

The environment was very primed for tornadoes after dark. Strong forcing was occuring with the upper system, seen in the 500 mb NAM/WRF forecast graphic above. The RUC model was forecasting strong combinations of CAPE and low-level shear (storm-relative helicity or SRH) well in advance of this event, seen in the first part of the forecast graphic above. The second half of the same graphic suggested a very moist, surface-based environment forecast in the same area, with large low-level CAPE.

A modified RUC analysis sounding at Ardmore (also seen above) as the tornadic cell was passing to the north and west, also suggests that an excellent setting for strong or violent tornadoes was present. Instability was large for after dark at this early time of year, with MLCAPE > 2500 J/kg, while 0-1 km SRH was also very large (> 500 m2/s2) for support of low-level rotation in storms. Deep layer shear was quite strong, approaching 60 kts to intensify updrafts, and low-level MLCAPE below 3 km (> 250 J/kg!) indicated a strongly surface-based setting with essentially no inhibition (MLCIN).

Excellent tornado warnings were issued for this storm by the National Weather Service. Better awareness and action by the public in response to such warnings and settings is what will save more lives with nighttime tornadoes.

My wife Shawna will be giving a talk at the Denver Chaser Convention this weekend (Feb 14-15) about how chasers can help with severe weather education, and be better prepared to assist in first response situations. This deadly early season Oklahoma event reminds me that it's an important talk.

- Jon Davies 2/11/09

Talks at Denver Storm Chaser Convention 2/14/09 and 2/15/09

2009-01-31T05:12:00.000-08:00

I will be doing 2 talks at the Denver convention this year: "Thoughts and Research on Nighttime Tornadoes and Rain-wrapped Tornadoes", and "A Review of Some Recent Tornado Settings from a Chase Forecast Perspective". There will several excellent speakers, including Rich Thompson of SPC talking about tornado forecasting, Dr. Howie Bluestein on VORTEX-II, and also Dr. Steve Lyons and Dr. Greg Forbes from The Weather Channel.

In addition, my wife Shawna will be doing what I think is a very important and down-to-earth talk for chasers, "Beyond the Storm - Chasers Helping with Communities and First Response". See: http://chaserconvention.com.

I understand there may be live online streaming of convention talks this year. So I hope you can make it to Denver, or at least watch online.

- Jon Davies 1/30/09

EF-1 tornado in Alabama on 1/10/09: a subtle small CAPE setting

2009-01-12T09:07:00.000-08:00

A weak tornado occurred shortly after 2300 UTC (5 pm CST) on Saturday, Jan. 10, about 30 miles north of Mobile in southwest Alabama. It wasn't very impressive (1-2 mile path, EF-1 winds around 100 mph), and thankfully no one was hurt, but it did do some damage (see NWS photos above, also click here). Given the subtle setting, it was kind of interesting from an environment standpoint.

Radar reflectivity at 2304 UTC from Mobile above shows the tornadic cell, and NWS Mobile did a good job with tornado warnings that were issued across southern Washington county for more than 45 minutes before the tornado struck the town of McIntosh.

The RUC analysis profile above for Mobile (MOB) at 2300 UTC is somewhat unusual, with small total CAPE (only around 400 J/kg!), and most of the CAPE below 600 mb, very low to the ground. Settings like this can enhance stretching near the ground, and with decent SRH (> 200 m2/s2 in the lowest 1 km), they can occasionally support tornadoes, even with small total CAPE.

The SPC graphics above show a large positive tilt 500 mb trough was heading southeastward, with a cold front (not shown) ahead over central Tennessee into central Mississippi. The Alabama tornadic cell occurred well in advance of this front in a moisture axis of 60s F dew points. In the parameter graphics, the SPC total MLCAPE field over southwest Alabama wasn't impressive (> 250 J/kg), but low-level CAPE was large (near 100 J/kg below 3 km) along with low-level SRH (200-300 m2/s2) overlapping the southwest Alabama moisture axis. These ingredients, combined with the low-to-the-ground vertical CAPE distribution in the RUC analysis above, were just enough to help generate a tornado with the cell north of Mobile.

This case is a reminder that storm environments with CAPE "squeezed" low to the ground certainly aren't limited to cold-core events (for example, see here).

- Jon Davies 1/12/09

Damaging thunderstorm winds in south Kansas City on 12/27/08

2008-12-28T08:03:00.000-08:00

It's unusual to get severe thunderstorms in the Kansas City (KC) area around Christmas, but it sure did happen yesterday morning (Saturday 12/27). The setting involved a very strong upper trough that brought unseasonably warm air northward ahead of it (record temps in the 60s F in KC on Friday), and an early morning bow echo type thunderstorm feature that interacted with a quasi-stationary outflow boundary in the south KC area.

The first graphic above shows the deep mid-level trough around midnight going into early morning on 12/27, along with SPC storm reports, and a WRF forecast of low-level CAPE suggesting an unstable surface-based environment extending northward into the KC area overnight. The 2nd graphic is a radar reflectivity image showing an ENE-WSW outflow boundary in place across the south KC metro area at 4:00 am, the result of thunderstorms that had moved across to the north of KC in the 2-3 hours prior. The bow echo thunderstorm feature is also visible approaching KC from the SW. Surface temperatures south of the ENE-WSW boundary were in the low-mid 60s F, while north of this same boundary, temperatures were at least 10-15 F colder as a result of storm outflow.

The 3rd graphic is a RUC analysis profile estimating the environment just south of the ENE-WSW boundary at Olathe KS (OJC) about 40 minutes before the damaging winds hit Johnson County (the SW side of the KC metro area). Although there was not a lot of CAPE (maybe about 200 J/kg), the profile was fairly surface-based with a deep low-level moist layer and around 50 J/kg of CAPE below 3 km. Also notice how strong the southerly low-level winds were at only 2000 ft above the surface (roughly 900 mb), with sustained speeds to 50 kts (nearly 60 mph)! It wouldn't take much storm downdraft to move these winds downward to the surface, particularly in a surface-based setting like that just south of the ENE-WSW boundary. In contrast, the 4th graphic above is a RUC profile at KC International Airport (MCI), roughly 20-25 miles north of the same boundary. Notice that with colder temps north of the boundary, this profile is "elevated", with no CAPE at all from lifted parcels in the lowest 100 mb. Even though the strongest part of the radar bow echo went across northward near the airport, the damaging winds were limited to the area along and just south of the ENE-WSW boundary. That's probably because that's where the warm surface-based environment was, where it was relatively easy to move strong winds downward from not far aloft, whereas farther north the cold near-surface setting probably kept damaging downdrafts from reaching the ground.

The last graphic above is both reflectivity and velocity showing the strongest winds coming into the south KC area around 4:40 am, reaching measured speeds around 80 mph. This was south of the strongest radar echo, but along the advancing outflow southeast of the bow echo feature. Again, that's where the warm surface-based setting was (south of the ENE-WSW boundary), better for allowing damaging winds to reach the surface.

What a weird week in the KC area... sub-zero (F) temperatures early on (Sun-Mon), then temps recovering to record high levels on Friday with thunderstorms, and back to ice and snow during the day on Saturday. On Friday evening, Shawna and I found ourselves driving in a heavy thunderstorm in north KC with sharp CG lighting, then getting up to ice covered trees on Saturday morning while more storms raged to our southeast. If you live in the Plains, just wait a few minutes... the weather will probably change :-).

- Jon Davies 12/28/08

Twin Horseshoe Vortices! (6-17-08 in Nebraska)

2008-11-23T10:01:00.000-08:00

Looking back at some photos my wife Shawna took on 6-17-08 while we were in northwest Nebraska waiting for storms to develop, I ran into these shots above that we had forgotten about. We've both seen plenty of "horseshoe vortices", but never a twin pair like this, south of Alliance. Shawna has a good eye for picking them out (I would have missed these).

There are probably several ways such vortices can form, but the most common idea is shown in the black and white explanation figure above. As a cumulus updraft builds, it may encounter rapid and strong vertical wind shear (differing wind speeds and/or directions within a short distance of height). This may cause the updraft to develop horizontal spin that, when stretched further by the small updraft, spins faster and is deformed into a "horseshoe" shape. Condensation within the cloud allows us to visually see the vortex. As dry air mixes into the cloud, it evaporates, except for the spinning horseshoe vortex, which resists dry air entrainment for a little while longer. In reality, horseshoe vortex formation is complex (otherwise they would happen all the time), but the diagram above summarizes some basics.

An estimated wind profile for Alliance is also shown above. Note the rapid and sharp wind shift from southeast to northwest at about 3000 ft above ground. This may help explain the horizontal spin that developed and stretched into "horseshoe" shapes with condensation as these cumulus updrafts on 6-17-08 encountered this sudden wind shear with height.

I don't think I've ever seen a photo of twin horseshoe vortices before. Thanks, Shawna, for catching these!

- Jon Davies 11/23/08

Southwest Kansas cold core setup on 11/10/08 - Mike Umscheid photographs large tornado

2008-11-11T04:33:00.000-08:00

Lead forecaster at NWS DDC and storm chaser/photographer extraordinaire Mike Umscheid documented a rare Kansas November wedge tornado, in the far southwest corner of the sunflower state yesterday. Wow! Go to: http://www.underthemeso.com/blog/ to see and read more.

The setting was a cold core setup (read paper here), with a 500 mb low attempting to cut-off over eastern Colorado within a strong upper wave lifting northeast (see SPC graphics above). An area of CAPE was over southwest Kansas, just east of the surface low where boundaries intersected (a fairly classic localized setup, see surface map above). The cell Mike chased looked to be pretty close to this key boundary intersection (see radar above), with sunny skies to the south on satellite (not shown), generating a good surface heat axis pointing into the area.

The RUC analysis sounding in the Johnson/Ulysses KS area at 21 UTC (see above), about 20-25 minutes before the tornado, showed good CAPE for a cold core setup (near 700 J/kg), all bunched below roughly 400 mb for a classic small supercell profile. With plenty of really cold air aloft (-10 C at 700 mb!), dew points in the 40s F and temps in the 50s F were all that was needed. Amazing!

A potential cold core setup in South Dakota last week (11/5/08) didn't pan out for tornadoes, as there appeared to be way too many low clouds for needed surface heating and instability near the boundary intersection with that system, unlike the one in southwest Kansas yesterday.

Excellent job, Mike!

- Jon Davies 11/11/08

New Severe Storms Conference paper online

2008-10-14T16:36:00.000-07:00

I won't be able to go to the 24th Conference on Severe Local Storms in Savannah, Georgia later this month. But I have submitted a paper for the online preprint, titled "Three Strong Tornadoes in 2008 associated with Boundary Intersections and Narrow Instability Axes near 700-mb Lows". The final version is now online HERE.

The paper focuses on 3 strong tornado events (see photos above) that were difficult to forecast in 2008:

- May 1 in northwest Iowa (F2 tornado near Rock Valley)
- May 22 in Colorado (the F3 Windsor tornado, with 1 death)
- June 6 in north-central Minnesota (F2 and F3 tornadoes near Park Rapids)

These had some features and ingredients that were similar to so-called "cold-core" events, but probably wouldn't be considered as such using a rigid definition. While the paper is not anything "earth-shattering", I hope some people find the case studies useful.

- Jon Davies (updated 10/22/08)

High Plains presentation now online

2008-10-05T08:41:00.000-07:00

Andy Fischer of NOAA/AWC Kansas City and I submitted a paper to the 12th Annual High Plains Conference (Hays, Kansas Sept. 4-5), "Significant Nighttime Tornadoes in 2008 Associated with Relatively Stable Low-level Conditions". I could not attend, so Andy presented the paper. Andy's presentation is now online in PDF format here.

The presentation focused on the setting and environment with the Beloit-Jewell-Belleville tornadic supercell in northern Kansas on 29 May 2008, and the Salina-Chapman-Manhattan supercell in central/northern Kansas on 11 June 2008. Both storms were associated with unusually large CIN for such intense tornadoes. MLCIN from lowest 100-mb mixed-layer lifted parcels was large for both events, probably between -120 and -170 J/kg, depending on the computer model used. This seems very large for significant tornadoes based on my database study from a 2004 paper in Weather and Forecasting.

What we found was that 0-1 km storm-relative helicity (SRH) was also unusually large (500-800 m2/s2) for these two supercell tornado events, particularly on 29 May. When combined with moderate total CAPE (at least 2000 J/kg) and strong deep shear (at least 55-60 kts), it appears that the environments for these events supported and enhanced intense mesocyclones to the extent that they were able to overcome the stable near-ground layer to generate tornadoes. Andy's presentation suggests that these combined ingredients (unusually large SRH, strong deep shear, at least moderate CAPE) can definitely support tornadoes in large CIN warm sector environments, and should be noted carefully by meteorologists, even when CIN suggests that an environment is not strongly surface-based. I'm hoping to post some addiitonal material on these events in the near future.

- Jon Davies 10/5/08

Tornadoes on 9/12/08 near Kansas City

2008-09-14T09:14:00.001-07:00

A somewhat rare September tornado episode occured on Friday 9/12/08 in the Kansas City area. While visually impressive (see photos above near Eudora & Desoto, Kansas), the tornadoes were weak, with damage only in the EF0-EF1 range (the National Weather Service has officially rated the tornadoes near DeSoto, Kansas and Sedalia, Missouri EF0 in intensity).

Shawna and I had a birthday celebration planned in north KC for her son Zach on Friday evening, so we missed alot of the excitement. When picking up Zach from school in Plattsburg, Missouri at mid-afternoon, Shawna and I noticed SE to NW bands of low dark clouds with rapid motion, suggesting strong low-level wind shear. With rain all day and a cool surface air mass north of a boundary to our south (see surface map above), I didn't give the setting much thought until Shawna saw what looked like a wispy funnel that lasted a few seconds under a cloud band in the distance. I looked at some maps online, and began to wonder a bit what might happen. SPC issued a tornado watch around 4:30 pm with tornado reports coming in to the southwest of Kansas City near the boundary, but we were committed to our celebration. Watching TV later at Shawna's parent's house, we saw how large the tornado near DeSoto was, and heard about reports of damage. Thankfully, the tornado warned cells that went over the KC metro area did not produce any damaging tornadoes.

The DeSoto, Kansas tornado was a classic case of a supercell crossing a boundary where wind shear increased rapidly, with easterly surface winds. The surface map above shows the stationary front in the Topeka-Olathe area, and the SPC maps above show the large increase in low-level wind shear (storm-relative helicity or SRH) along and north of the front, with CAPE near and south of the front. The best combination of CAPE-SRH was right along the front just south and southwest of the KC metro area. Deep-layer shear through 6 km above ground (not shown) was also on the order of 40 kts along and north of the front, suggesting good support for tornadic supercells. On radar images above, notice how the DeSoto cell (indicated by white arrow) crossed the boundary moving northeastward, which is about the time it produced a tornado. As this cell moved deeper into the cool surface air north of the front, it stopped producing tornadoes.

The RUC analysis profile at Olathe (OJC, also shown above) is interesting, showing a large veering wind profile in the lowest 1-2 km, and around 900 J/kg of CAPE. While the instability wasn't super-impressive, notice that it was bunched low in the profile, with the "fattest" CAPE roughly 13,000 ft above ground. Most warm-season tornadic thunderstorms average larger CAPE, with the "fattest" CAPE up around 24,000-30,000 ft above ground. With the CAPE in the Olathe profile "squeezed" down fairly low, that suggests more rapid movement of air accelerating upward, like a hot air balloon encountering cold air aloft and moving upward faster. This could help with upward stretching, and combined with the wind shear, might be another factor to help increase potential for a tornado in a "smaller CAPE" environment.

- Jon Davies 9-14-08

Denver area landspout setup on 8-24-08

2008-08-27T09:28:00.001-07:00

With the Democrats tooling up for their convention this past weekend in Denver, weather tried to steal the show for a bit with a long-lived landpout tornado (see picture sequence courtesy of KUSA above) just southeast of the Denver Metro area.

The setting was fairly typical for landspout tornadoes (a form of non-mesocyclone or non-supercell tornado) near Denver, with a boundary NE-SW across the metro area (see surface map above). Storms formed along this boundary just south of Denver between 4:00 pm and 5:00 pm MDT. Then another sharper southeastward-moving boundary moved off the foothills to the west (see radar image above), and collided with the storms over the southern metro area. These colliding boundaries and the storm updrafts stretching the vorticity ("spin") along them produced the long-lived landspout tornado over northeast Elbert County between 5:30 PM and 6:00 pm MDT, as well as a couple other briefer landspouts elsewhere along the line.

A sharp windshift boundary (or colliding boundaries in this case) is the most important component in landspout cases, providing the vertical "spin" to be stretched into a tornado. But the environment contributes as well, with strong surface heating and rapid temperature change (steep lapse rates) in the lowest 2 km or so, helping to accelerate air parcels upward in low-levels to augment stretching by storm updrafts along the boundary or boundaries (see Davies and Caruso 2005 at http://www.nwas.org/ej/cardav/). Such environments are similar to those that encourage dust devils on hot days.

Above, a RUC analysis profile in the southeast Denver metro area shows these very steep low-level lapse rates, and also the deep well-mixed moisture layer, even though cloud bases were high (MLLCL around 2500 m AGL). I used to think that some low-level CAPE (e.g., CAPE below 3 km AGL) was needed in these events, but I've seen several Colorado events in recent years where this just isn't the case. It seems that a deep well-mixed moist layer (to reduce parcel entrainment and drying) with little if any CIN (to let parcels rise rapidly) is what is really needed, along with the steep low-level lapse rates, and of course, the boundary or boundaries. These ingredients thrown together in the same area increase the chance of a mesoscale "accident" that might result in a landspout tornado. With the local topography around the Denver area that can help set up boundaries on days with steep lapse rates, such events are relatively common there.

- Jon Davies 8-26-08

Niagara Falls trip & photos

2008-08-17T08:14:00.000-07:00

This isn't directly related to weather, but Shawna and I went to Niagara Falls last weekend for a very pleasant trip. The sky was picturesque with lots of bubbly cumulus clouds against crisp blue, courtesy of an upper trough with cold air aloft moving through. With that as background, the falls were truly beautiful!

Above are some photos. The first is the American side of the falls, with the city of Niagara Falls, New York, visible. But I think the Canadian side of the falls is more magnificent, in the remaining shots. Shawna, as seen in the second image above, agrees. Enjoy!

- Jon Davies 8/17/08

6/11/08 Little Sioux-Moorhead, Iowa tornado path revisited - solving a "mystery"

2008-08-03T04:58:00.000-07:00

The Little Sioux campground EF3 tornado was one of the more publicized tornadoes in 2008 because of 4 boy scouts killed when it destroyed a bunk house where they had been drilled to take shelter (see my earlier post in June). Near the end of the 14 mile track (see first map shown above), this tornado struck storm chasers Kelly Martinson (also known as Kory Hartman) and Kenny Allen as it crossed Highway 183 a couple miles southwest of Moorhead, Iowa, yielding the most impressive up-close example I've ever seen of what it is like to encounter a rain-wrapped tornado. Contrary to some speculation by other chasers online, Kelly and Kenny did not intend to get that close, as the tornado was embedded in rain and the Omaha radar went down near the time of their encounter, making it difficult to judge where the tornado was as they waited for the mesocyclone to approach from the southwest. Also above are images of the same rain-wrapped supercell near Moorhead (observed by storm chasers from Iowa State), and later northwest of Dunlap (from the viewpoint of Shawna and myself).

The ground survey by NWS Omaha the day after the tornado suggested that the tornado did not cross highway 183 southwest of Moorhead, but Kelly and Kenny's video and their personal survey information indicated that it did (see the second map above, a Google maps closeup of the path end showing the discrepancy between the 2 survey tracks). To solve this mystery, Shawna and I revisited the area southwest of Moorhead on a trip to Iowa about a month after the tornado. Using a reference copy of Kelly and Kenny's video provided by Doug Kiesling (see video grab insets on second map above), Shawna and I located where the tornado crossed the highway (see third map above, my own survey of the tail end of the tornado track). From fence damage just west of highway 183 and south of 314th street (see photo above), it was clear that the most intense part of the tornado (50-100 yards wide) did indeed cross the highway where Kelly and Kenny's map indicated. We also found the two broken road signs that are seen being snapped off in Kelly and Kenny's video. Without the video the day after the tornado, it would have been easy to miss this damage, as the fence is located below and some distance west of highway 183 in a treeless area, and the broken signs were hidden in tall grass. Tree damage along and north of 314th street (what was shown as the center of the tornado path in the official survey) appears to have been a result of the north edge of the broader tornado circulation, or possibly inflow winds coming into the tornado from the north or northeast (see my close up map above). This example goes to show that surveying damage is difficult, and not always an exact science, particularly in rural areas.

Also, important to note: The intensity of the low-to-the-ground fence damage lined up with highway 183 strongly suggests that, had Kelly and Kenny been located another 50 yards southwest on highway 183, their vehicle would most likely have been rolled off the highway down a steep embankment, possibly resulting in injuries (the swirling condensation marking the most intense part of the tornado can be seen passing just south of their vehicle on the video). So, they are very lucky... as is the occupant of another vehicle (tail lights seen on the video) a few hundred yards farther down the highway (the most intense part of the tornado passed between the two vehicles). This is a graphic illustration of how dangerous it is to chase high-precipitation supercells with rain-wrapped tornadoes, as well as the potential problems of relying entirely on radar information when you can't see very well.

- Jon Davies 8/3/08

Nontornadic supercell in northeast Kansas - 7/24/08

2008-07-26T11:06:00.000-07:00

It's been awhile since I've posted... I've been enjoying (and getting adjusted to) married life!

Last Thursday evening (7/24/08), Shawna and I storm chased in northeast Kansas during what appeared to be a fairly promising tornado setup for July. SPC even issued a tornado watch extending southeastward across the Kansas City area (see the insets on surface map graphic above). But, apart from a supercell along the Nebraska/Kansas border that rapidly gusted out and moved southeast into a line (see our photo images above), not much happened, and there were certainly no tornadoes. Why?

One can only speculate. Here's some thoughts...

Thunderstorm outflow from morning storms over Missouri had reinforced a stationary front/boundary during the day over northeast Kansas that was quite evident at late afternoon and early evening (see the surface map above). Even though wind shear was strong with easterly winds north of this boundary, temperatures were 10-15 degrees F colder on the cool side of the boundary in extreme northeast Kansas and southeast Nebraska where the original supercell developed between 5 and 6 pm CDT. Radar images above show this storm at 6 and 7 pm CDT, respectively, and its location is also marked with a circled "S" on the surface map above.

At Falls CIty, Nebraska (FNB), located just east of where the supercell formed, a RUC analysis profile at 6 pm CDT (shown above) indicated a good wind profile for tornadoes (a clockwise looping hodograph) and good CAPE (instability). BUT, the low-levels were rather stable (blue area on the RUC profile) beneath the CAPE area (red area on the RUC profile). Because tornadoes are a surface-based phenomenon involving near-surface air parcels, this low-level stable area with the cooler surface air may have been a negative factor, particularly because the supercell stayed north of the boundary.

I've noticed (as have other researchers) that when supercells form and _stay_ on the cool side of a significant boundary, they are less likely to produce tornadoes than if they _cross_ the boundary from warm to cool, or develop and stay within the warm sector (if there is significant warm sector wind shear, too). It may be notable that a couple storms that produced surprise tornadoes in north-central Missouri on 7/21/08 (no, we weren't there) occurred on the warm side of a prominent boundary. So the location of the supercell relative to the cool side of the boundary may be one clue in this case as to why no tornadoes happened. In addition, the cooler, heavier surface air on the cool side of the boundary may have made it easier for the storm's outflow to gust out, undercutting the mesocyclone and setting up a more linear configuration. But that's also speculation.

Anyway, it made for an interesting storm chase not too far from home (N of Kansas City).

- Jon Davies 7/26/08

Our Storm Chase Wedding - Jon & Shawna Davies

2008-06-20T16:54:00.000-07:00

Shawna Helt and I were married at the end of a storm chase yesterday (Thursday June 19) in the Konza Prairie near Manhattan, Kansas. We had talked about doing this on a storm chase for a couple months, and hoped we could pull it off on our chase vacation. We did it!

I am so delighted now to have Shawna as my wife!

Thanks to Rick Schmidt, Dick McGowan, and Jim Reed for sharing their pictures above!

Thanks to Aaron Blaser (in blue Hawaiian shirt) for officiating the ceremony and coordinating things!

And thanks to all our chaser friends who could attend on very short notice after driving through several heavy rain cores to be with us:

Aaron and Wendy Blaser
Kyle Gerstner
Doug Nelson
Rick Schmidt
Dick McGowan
Darin Brunin
Evan Bookbinder
Katherine Bay
Jim Reed
Robin Lorenson
Mike Phelps

Many thanks, too, to all those who have sent us their congratulations!

- Jon Davies 6/20/08