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

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?

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

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

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