Thursday, December 31, 2009
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
Tuesday, November 24, 2009
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
Sunday, October 25, 2009
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
Thursday, October 15, 2009
Additional air dates through October 30 (these are tentative!) are listed below:
Times EDT, not CDT !
TR1 8p and 2a
TR2 9p and 3a
TR2 9p and 2a
TR3 10p and 3a
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
Sunday, September 20, 2009
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
Saturday, August 22, 2009
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
Monday, August 17, 2009
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
Sunday, August 2, 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
Sunday, July 26, 2009
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
Sunday, July 12, 2009
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
Sunday, June 21, 2009
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
Monday, May 18, 2009
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
Thursday, April 30, 2009
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
Sunday, April 19, 2009
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
Sunday, March 29, 2009
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
Thursday, March 19, 2009
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
Tuesday, February 17, 2009
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:
- Jon Davies 2/17/09
Wednesday, February 11, 2009
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
Saturday, January 31, 2009
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
Monday, January 12, 2009
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