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

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

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

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

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

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

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

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