Friday, July 27, 2012

Lightning article featuring Tim Samaras in August National Geographic

As I wrote in this blog a month ago, I'm taking a break this summer from case study posts.  However, I do want to mention that National Geographic is running an excellent article on my severe weather researcher friend Tim Samaras and his lightning photography quest. 

The article and accompanying images are in the August 2012 issue of National Geographic magazine.  Here's the cover:

credit: National Geographic

And here are some images from the article, shown with National Geographic permission:

© Carsten Peter

© Carsten Peter

© Carsten Peter

Here's an online link to other photos:

A portion of Nat Geo's press release:

Using the world's fastest high-resolution camera housed in a mobile trailer, Tim Samaras hopes to be the first to photograph the micro-second event (not visible to the naked eye) that triggers a lightning strike. Through this, Samaras hopes to discover clues to some of lightning's biggest mysteries: Why will a lightning bolt sometimes strike a low tree when right beside it is a tall metal tower? And why, for that matter, does lightning strike at all?

He is used to having people tell him that what he’s trying can’t be done. But before he became obsessed with lightning, Samaras spent several years chasing after tornadoes to deploy electronic probes, mounted with video cameras and other instruments, to record what it looks and feels like from inside.  People were dubious about that too, but he managed to gather some of the most accurate readings ever of wind speed, barometric pressure, temperature, humidity inside a tornado vortex.

Congratulations, Tim...  As always, great work!

Jon Davies - 7/27/12

Saturday, June 30, 2012

Taking a break...

Wow... June has gone by and no blog posts.  I've had a lot going on personally the last month, and there's a bunch of stuff for me to work through the rest of the summer.

I'm going to continue to take a break to sort some things out.  Sorry about that.  I know I have a small loyal following of weather enthusiasts who like to read and learn about severe weather and forecasting.  I'll see if I can get back to posting some occasional case studies this fall.
For those who read my stuff, thanks so much for your patience.

Jon  6-30-12

Sunday, May 20, 2012

Prolific non-supercell tornado outbreak in Kansas 5/19/12 !!!

Yesterday (May 19) in south-central Kansas was a great reminder that potentially strong tornadoes (see images above near Rago KS in the 6:30-6:45 pm CDT / 2330-2345 UTC time frame) can occur once in awhile without the typical supercell processes that involve large low-level wind shear or storm-relative helicity.  I've written peer-reviewed papers on this subject for NWA Electronic Journal (2005, see here) and Weather and Forecasting (2006, see here).  In particular, the setting shown in the 2005 NWA paper with Jim Caruso matched what happened yesterday (which was largely unexpected) quite well.

Non-supercell tornadoes that we tend to call "landspouts" (because of their seeming similarity to waterspouts, but over land) generally occur on sharp boundaries and get their "spin" from stretching of vorticity associated with the sharp wind shift, often seen as a fine line on radar or even satellite (see the frontal boundary in south-central KS on the satellite image above).  While the boundary is the most important ingredient, the environment usually includes steep low-level lapse rates (a rapid drop in temperature above ground) in the lowest 1 or 2 km due to strong surface heating and no temperature inversion (little or no CIN or convective inhibition), along with well-mixed low-level moisture.  Such tornadoes can occur even if the spread between temperature and dewpoint is large and cloud bases (LCLs or lifting condensation levels) are quite high, unlike supercell tornadoes. Notice that the Rapid Refresh sounding above, 30-40 minutes before yesterday's first tornadoes, had all these characteristics.  Such a profile would promote rapid low-level upward stretching under storm updrafts, and if the stretching with thunderstorm updrafts were to occur directly over a wind shift boundary with vertical vorticity or "spin" along it, that would increase the chance of tornadoes.

The morning NAM and HRRR forecast panels above for mid to late afternoon on Saturday suggested that these ingredients (boundary, steep lapse rates, low-level moisture with little CIN, and convection on the boundary) might be in place for a "mesoscale accident".  Short-term forecasting of such set ups is never easy and depends on everything coming together just right.  But certainly, with so many tornado reports in the Kingman/Harper County area of south-central Kansas during the 90 minute period 5:30-7:00 pm CDT (2230-0000 UTC), including one tornado that significantly damaged wind farm turbines, everything came together in spades.

The surface map and SPC mesoanalysis panels above show these same ingredients coming together in real-time on the 2200 UTC panels before the tornadoes.

In contrast, the next SPC panels above include 0-1 km storm-relative helicity (SRH) at 2200 UTC, showing how poor the low-level shear environment was yesterday in regard to supercell processes.  However, the surface vorticity panel by it shows how much vertical vorticity was focused and available with the boundary for non-supercell processes.

The 3 radar panels above also show some interesting mesoscale features. Along with the storms "back-building" to the south-southwest like a "zipper" on and directly over the boundary (common in prolific "landspout" events), notice the southwestward-moving outflow boundary (another radar fine line) visible behind the frontal boundary. As this intersected the frontal boundary progressively southward, it appeared to help in the generation of successive tornadoes, including the tornadoes near Rago KS tornado that occured in northern Harper County KS about 15 minutes after the last image above.  I've seen this before in prolific landspout events when the radar is close enough to see it, and it could be an important issue in the production of stronger "landspout-type" tornadoes.

One other issue I will mention is the Non-Supercell Tornado parameter (NST, not shown) found on SPC's mesoanalysis site.  It performed _horribly_ yesterday, showing no values at all during the outbreak.  I'll have to look back at the ingredients that go into the NST parameter, but my impression is that it depends too much on the presence of low-level (0-3 km) CAPE, which may or may not be part of the environment in "landspout" settings (see the earlier sounding).  What's probably more important is well-mixed moisture in the lowest 1-2 kilometers along with the steep low-level lapse rates, and a lack of CIN (convective inhibition) and absence of a temperature inversion that might otherwise slow stretching in low-levels.  If I were writing the papers now that I referenced earlier, I would modify my description of these ingredients.

At any rate, as I've heard Chuck Doswell say many times, there are many ways to get a tornado.  Mother Nature doesn't care if the vorticity to be stretched is from SRH (tilted horizontal vorticity) or a sharp wind shift boundary (localized vorticity already oriented vertically).  A prolific non-supercell tornado setting like yesterday doesn't happen very often, but for tornado forecasters it is definitely one to get familiar with and watch for.

- Jon Davies  5/20/12

Update:  Wichita NWS (see here) has rated one of Saturday's tornadoes that struck a farm northwest of Harper as EF3 in intensity. That's pretty impressive for an event driven primarily by non-supercell tornado (NST) processes.  It seems that the more prolific an NST event and the longer it goes on, the more intense and "supercellular" in nature the tornadoes can become, particularly if deep layer wind shear is significant (around 35 knots in this setting).

Saturday, May 5, 2012

Strong cap eliminates Nebraska tornado potential on 5/5/12

Saturday 5/5/12 over Nebraska was a good example of a "cap" bust where the surface warm sector was overlain by warm temperatures aloft at around 10,000 ft MSL (the "cap", see 700 mb 9 deg C isotherm on SPC graphics above through the day) that kept warm sector storms from forming.  This effectively eliminated any tornado potential for a day that had looked much more threatening on computer models a couple days before.  My wife Shawna and I saw this looking at morning and early afternoon data, and were concerned that daytime storms would be limited to the elevated environment north of the surface front .  So we elected not to storm chase today.

The chart above is a rough seasonal guideline I use regarding 700 mb temperatures that estimate the "cap" during maximum heating in the Central Plains.  Notice that 9 deg C (give or take a degree) is a very rough estimate of the "cap" in early May, and that was a good indicator today using the earlier SPC graphics.

The SW-NE stationary surface boundary over Nebraska (see map above) was "covered" by this cap through most of the day, which kept storms from initiating over central and northeast Nebraska in the warm sector.  It can also be seen on the SPC SBCAPE and EHI graphics above that the first cell to form in the evening was well north of this surface boundary in South Dakota and far away from a truly surface-based environment.  Storms did form in a line around and after dark behind the front (not shown) as the cap eroded from the west with the approach of an upper short wave of energy.  But the warm sector tornado threat was eliminated by the cap.

Yesterday, it came to my attention that someone was passing around Facebook a version of the SRH-CAPE chart I posted last year to suggest environment potential (low-level wind shear and instability) for significant tornadoes, using that to show how 5/5/12 would be a big tornado day in Nebraska.   Well... What actually happened on 5/5/12 is major reminder that tornado forecasting is about a lot more than just environment...  It involves assessing the surface pattern and warm sector orientation relative to where storms initiate (see my last post about April 27), as well the positioning and evolution of any "capped" areas that can keep storms from developing.  Severe weather forecasting is not simple stuff.

- Jon Davies 5/5/12

Monday, April 30, 2012

April 27 and April 21, 2012: Examples of boundaries hurting & helping tornado potential

Last Friday's (4/27) SPC outlook with a moderate risk and strong tornadoes expected in central and eastern KS did not really verify (there were only 2 or 3 very brief EF0 tornado reports with no damage). Looking back, this case was a good example of a narrow warm sector where, although ingredients (CAPE and wind shear) looked very supportive of supercell tornadoes, storms persistently formed too close to a surface stationary frontal boundary.  They moved across it and into a cooler surface environment where they rapidly became elevated supercells (not surface-based), with the only lifted parcels that could produce CAPE/instability coming from well above ground, which worked against tornadoes.

To illustrate this, the first graphic above shows surface-based (SB)CAPE and storm-relative helicity (SRH, low-level wind shear) from the SPC mesoanalysis at 7 pm CDT when a tornado-warned storm was moving into Topeka KS from the southwest.  Notice how far north of the surface warm sector (indicated by SBCAPE) this cell was located.  As seen from the Topeka Rapid Refresh sounding at the same time (2nd graphic above; no observed sounding was done due to ongoing severe weather), this environment was clearly elevated, with no CAPE from lifted parcels near the ground.  Even though SRH was quite large, it is difficult for tornadoes to develop in such an elevated setting north of a stationary surface boundary, and any tornadoes that could manage to develop here would be weak and very brief.   Because supercell storms could not spend much time in the surface-based warm sector before crossing the stationary boundary into much cooler surface air, the supercell tornado threat as originally anticipated could not materialize.

The Saturday before (4/21) in the northern plains saw another type of boundary generate a surprise round of weak (EF0-EF1, see storm report map and photo above) tornadoes in western Minnesota that were not expected.  These were non-supercell tornadoes that developed from enhanced stretching processes along a sharp north-south surface wind-shift boundary that provided vorticity for spin.  With very cold air aloft, a vertically compact area of CAPE (see the sounding above) developed from surface heating accompanied by very steep low-level lapse rates.  Both of these factors increased the potential for strong low-level stretching as storms formed along the surface boundary, which resulted in several tornadoes that did some damage to farmsteads.  Notice on the SPC graphics above that the overlapping of steep low-level lapse rates with low-level CAPE suggested very well the enhanced stretching environment along and just west of the boundary (see my paper with Jim Caruso here).  This was also indicated by the SPC Non-supercell Tornado parameter (also shown above), which incorporates these same ingredients.

So, 4/21 was an example of a different type of boundary that helped rather than hurt tornado potential.  Fortunately, difficult-to-forecast events like these usually produce generaly weak tornadoes and don't happen that often.  One certainly would not expect tornadoes in April with northwest flow aloft and surface dew points only in the 40's F (quite unusual!!!).  But a look back shows that some required ingredients for non-supercell tornadoes were there.

- Jon Davies  4/30/12

Sunday, April 22, 2012

Tornadoes after dark most dangerous during April 14 outbreak

Much has been written and many photos posted from last week's major outbreak of tornadoes on Saturday April 14, 2012.   The most damaging and deadly tornadoes turned out to be after dark, including the EF3 tornado that hit the southeast side of Wichita KS ($140 million damage), and the EF3 tornado that struck the Woodward OK area around midnight killing 6 people.

Above, grabs from video by my wife Shawna near and after dark in the Moundridge-Goessel and Marion areas of central KS show tornadoes visible only by lightning, including a large one near Marion Lake.  Associated maps and radar images above also show the tornado paths from that supercell, as well as the more prolific supercell that struck Wichita around 10:20 pm and produced other tornadoes before and after, also after dark.

Tornadoes after dark are particularly dangerous because they are difficult to see, and many people are asleep and not aware of what's approaching.  My paper with Andy Fischer about nighttime tornado environments (see here) shows that tornadoes after dark in the Plains occur when both CAPE and especially low-level shear are large after sunset.  Just as important, storms after dark need to remain relatively "surface-based" (lifted parcels of air near the ground that feed updrafts are able to move upward with little resistance).  This occurs when surface temperatures don't cool much and surface dew points remain steady or even increase, keeping convective inhibition (CIN) relatively small, rather than the more typical scenario where storms become "elevated" above a cool stable layer near the ground when surface temperatures cool significantly after sunset.

CAPE below 3 km  (CAPE closer to the ground) can also be an indicator of a more surface-based environment.  Notice that in the 2 graphics immediately above, along with large CAPE-shear combinations (suggested by both the Sig Tor parameter and the energy-helicity index), there were significant amounts of low-level CAPE indicated after dark on both the SPC mesoscale analysis in real-time, and on model forecasts in advance.  This suggested a continuation of the April 14 tornado event well after dark, which was the case, particularly with the Wichita KS and Woodward OK tornadoes.

Obviously, with this big an outbreak, it is very fortunate that more people weren't killed.  I can't emphasize enough the excellent forecasts and outlooks several days in advance, as well as pin-point warnings and media coverage during the event.

When I get time this coming week, I'll do a post about the setting that generated tornadoes in Minnesota yesterday (4/21/12) with early spring northwest flow aloft and 40's F dew points at the surface (very unusual!).

- Jon Davies  4/22/12

Wednesday, April 11, 2012

"Surviving the Storm: What Storm Chasers Want You to Know" DVD now available!

As I announced at ChaserCon 2012 in Denver, my wife Shawna Davies has spent much of the past year putting together a 30-minute severe weather safety/preparedness program working with several other storm chasers, including James Skivers, Stephen Locke, and Bill and Anna Stromberg. It's now available on DVD for $13.95 at:
************** **************

With this project, Shawna wanted to use storm chaser knowledge and experience to do something good, apart from the usual storm chasing videos. Here's some excerpts from the Press Release:

With death and injury tolls from tornadoes in 2011 that were staggering, a group of professional storm chasers decided to use their considerable experience with violent weather to make an instructive and entertaining DVD to help people save their own lives when severe weather strikes. This DVD is titled “Surviving the Storm: What Storm Chasers Want You to Know”.

This 30 minute program provides life-saving tips and strategies for individuals and families to protect themselves against all types of severe weather... Safety segments show how to increase survival chances when violent weather strikes both indoors and out, including on the road. In addition, on-the-street interviews quiz people about severe weather knowledge with humor and wit, and a heart-pounding finale shows a mother and daughter acting to save their lives as a tornado strikes their home. Through use of exciting storm chaser footage and re-enactments of life threatening situations, this DVD offers an abundance of knowledge to survive deadly storms and severe weather.

With what appears to be a several-day period of severe weather coming up for the Plains during April 12 through April 16, now seems an appropriate time to announce this DVD. Please buy a copy and let your friends know about it, too. After a deadly year of tornadoes and severe weather in 2011, we really want people to be aware and prepared in 2012!


- Jon Davies 4/11/12

Saturday, March 24, 2012

Cold-core tornado kills 1 person in southern IL, March 23, 2012

Sadly, one of yesterday's cold-core tornadoes at midday over southern Illinois killed a woman in a double-wide mobile home near the small town of Opdyke (see photos above). It's rare that someone dies in a tornado related to a nearby cold-core mid-level low, as such tornadoes are usually weak and short-lived. This tornado did not appear particularly strong or long-lived, but hit in the wrong place at the wrong time, and will probably be rated either EF1 or low-end EF2. (As I write this, there's no information yet regarding tornado intensity from the NWS).

The same system produced many cold air funnels over Oklahoma on Wednesday March 21, and again over Kansas on March 22 (not shown). The main reason there were no actual tornadoes on those days had to do with the Pacific cool front surging far eastward into the Mississippi Valley, taking the potential surface boundary focus and true surface warm sector well east of the mid-level low spinning over the OK/KS area.

However, on Friday March 23, the mid-level low (see the NAM model 500 mb panel and satellite image above) was moving east again, moving closer to the surface Pacific front that had stalled near the Mississippi River with a surge/spoke of energy aloft. As a result, a new surface low was forming over the mid-Mississippi Valley (see surface map above), providing a surface boundary focus for vorticity and convergence where thunderstorms were building at midday over southern Illinois just ahead of the closed low and cold pool aloft.

One cell generated intermittent tornadoes from near Cape Girardeau MO to north of Carbondale IL. Another cell developed rapidly north of Marion IL and produced the killer tornado near Opdyke shortly before 1:30 pm CDT (1830 UTC). An estimated sounding from the new Rapid Refresh model (set to replace the current RUC model in April 2012) showed sizable CAPE at Marion IL over an hour before the Opdyke tornado, with nearly all instability located below 26000 ft (see the sounding diagram above).

While such a CAPE environment by itself won't support tornadoes with thunderstorms, when coupled with a good surface boundary focus that mazimizes available vorticity as on Friday in southern IL, CAPE "squeezed" into the lower part of the atmosphere can accelerate air parcels upward in storm updrafts to provide rapid stretching needed for tornadoes. There doesn't need to be a bunch of storm-relative helicity or SRH (notice that SRH on the sounding above wasn't large in yesterday's environment); the enhanced stretching with the cold air aloft over the northwest edge of the surface warm sector often seems to be able to do the trick with what otherwise looks like relatively weak SRH/low-level shear. (Note: When both SRH and CAPE are strong in cold-core settings, a somewhat rare occurrence, the associated tornadoes can be stronger and larger as well; see this blog post from last year.)

So, again, the surface boundary focus and proximity of the mid-level low (as well as surface heating from the sun) appear to be very important in producing tornadoes at the ground with cold-core systems. (For additional information, my peer-reviewed paper about "cold-core" tornadoes is here.)

- Jon Davies 3/24/12

Monday, March 5, 2012

Harveyville KS tornado article in Wichita Eagle misses some facts

An article here by Stan Finger in the Wichita Eagle yesterday about the recent Harveyville KS tornado (see my previous blog post last Thursday 3/1/12) claiming that there was "no warning" was not totally factual. There was indeed a severe thunderstorm warning issued that mentioned a tornado watch was in effect, as well as the possibility of tornadoes that could form quickly (see above). In my opinion, the way the article was edited (after talking by phone, I found out that the "no warning" headline was not Mr. Finger's responsibility) put the focus on the wrong issues, and was NOT helpful in improving public weather safety response and perceptions.

To be clear, the Harveyville tornado was light years away from the Joplin tornado in its brevity and weaker intensity, and it is ridiculous to focus on that isolated event compared to all the other tornadoes that occurred on Feb 29th and March 2nd when the National Weather Service did an exemplary job regarding watches, warnings, and public awareness. The article also came off, courtesy of quotes by Mike Smith, as a free advertisement for Accuweather's "superiorty" in detection and warning. In serving utility clients like Westar Energy, this corporate for-profit entity has none of the public responsibility and pressure that the National Weather Service has in an era where the general public wants to be warned about everything that affects them directly (an impossibility, even with our technology), but also thinks there are too many false alarms.

Here is an e-mail letter I sent to Stan Finger this morning:

Your article yesterday about the Harveyville KS tornado was disappointing, and really missed some facts.

First, there _was_ indeed a warning in effect for Harveyville when the tornado hit... a severe thunderstorm warning that specifically mentioned Harveyville and the possibility of strong winds (see attached). It also mentioned that a tornado watch was in effect and that tornadoes can develop quickly from severe thundertorms. So, your headline "Harveyville tornado struck without warning" is misleading and incorrect.

The brief and narrow Harveyville tornado lasted only 4 minutes and happened to go right down through town. Had it occurred a couple miles north or south of where it did, we might not have even heard about it. The small tight rotational signal that appeared on radar was truly visible for only one scan as it was upon Harveyville, with no time for an advance specific tornado warning.

The quotes you gave from Mike Smith were not at all in proper context, and were like comparing walnuts with oranges when talking about what Accuweather does relative to the National Weather Service. "Warnings" given by Accuweather are mainly for utility and transportation clients, who don't generally object to overwarning issues... they just want to be prepared and alert for power line breaks and transportation interruptions in specific locations, whether from strong straight-line winds or tornadoes.

So, Accuweather can issue tornado warnings continuously and indiscriminately along a long-track supercell's 3-4 hour path without public complaints and repercussions, regardless of whether verified damage is from winds or tornadoes. It's no big deal that Accuweather supposedly issued a so-called "tornado warning" for Westar and the Kansas Turnpike Authority some "4 minutes" before Harveyville... they were doing similar warnings along the entire supercell's path when _no_ tornadoes had been occuring for over 2 hours, even with what Mike Smith referred to as "persistent tornadic signatures" (actually a parent mesocyclone with _potential_ to produce tornadoes). Many storms show persistent strong rotation without producing tornadoes.

The larger issue here is the public perception of "overwarning" that came out of the Joplin tornado NWS assessment. Many people at Joplin (including some I talked to) complained that sirens are run too often, fostering a public perception that they are hard to take seriously. The NWS is attempting to address that perception this spring, and that puts them in a difficult position on events like Harveyville. Mike Smith and Accuweather have none of that pressure... they can warn every location in a storm's path for their corporate clients whether reports verify or not and claim they did a better job than NWS, even when they have no responsibility for actual public warnings and overwarning perceptions.

The reality is, even with radars that have faster scans and better technology, the National Weather Service (and Accuweather) cannot in real-time discriminate between tornadoes and other severe phenomena in many situations. Some tornadoes are just too brief. The public needs to understand this and not expect someone to come "knocking on their door" to personally warn them for every potentially severe event. There _was_ a severe thunderstorm warning for Harveyville at the time of the tornado, and also a tornado watch in effect.

People should be prepared and responsible for their own safety by taking all warnings and watches seriously. They can then monitor cell phone alerts, radar, television, and/or weather radios for additional information to assess their risk rather than expecting sirens to warn them specifically for _everything_. If a strong supercell on radar with a severe thunderstorm warning is approaching and your town is directly in its path, you should be prepared to take cover _fast_, regardless of whether or not a tornado warning is in effect or the sirens are blaring.

Besides missing some important facts, the general tone of the article you wrote yesterday did not help in this regard, and comes off as promoting private for-profit corporatations like Accuweather that have none of the public resposibilities and pressures of the National Weather Service. The National Weather Service did a superior job with watches, warnings, and advance public awareness on the March 2nd tornado outbreak 3 days ago, and many lives were saved. You didn't mention that in your article, and instead focused on NWS performance in a single isolated weather event.

In the future, please consider writing articles that constructively deal with important issues such as:
- The reality that no weather organization or corporation can warn or alert the public on every severe event, particularly brief or isolated ones!
- The public perception of overwarning vs. the public desire and expectation to be properly warned on everything that affects them directly. How does one even approach a solution to this? These are huge social issues!
- What can we do about the public ignoring severe thunderstorm warnings?
- As discussed above, the National Weather Service has some category of watch or warning issued to alert the public on the vast majority of weather events. This was certainly true with the Harveyville tornado. If people want to stay safe, they need to take some degree of responsibility for themselves by monitoring available weather information and taking appropriate action instead of relying completely on sirens and/or specific warning "categories".

Rather than write attention-grabbing headlines ("there was no warning"), let's get the facts straight and not mislead the public about difficult-to-detect events. Instead, let's educate and encourage the public to monitor the available weather information we have (which is of good quality) and take some responsibility for themselves.

Enough said...

- Jon Davies 3/5/12

Thursday, March 1, 2012

Harveyville KS February 28, 2012 - a difficult tornado warning situation

The tornado outbreak this past Tuesday evening into early Wednesday morning took several lives in Kansas, Missouri, and Illinois, and was an early reminder that spring is nearly here in the central U.S. Hardest hit was Harrisburg IL with an EF4 tornado killing 6 people around 5 am Wednesday morning. The first killer tornado (EF2, see damage photo above) hit around 9:00 pm the evening before, southwest of Topeka KS at Harveyville, claiming the life of one man who died later on Wednesday night.

This was a very difficult warning situation. The tornado only lasted about 4 minutes, but happened to go right down through the small town. Had the path been displaced a few miles north or south, we wouldn't have heard much about it. The parent supercell (see arrows on radar composite above) developed near Pratt KS more than 3 hours earlier, producing a brief tornado southwest of Hutchinson, but hadn't produced any other reported tornadoes for over 2 hours since that time. The rotational signature on radar at the time the tornado hit Harveyville was brief and small (see Topeka NWS radar images here). The Harveyville area had been under a severe thundertorm warning for about 30 minutes prior to the tornado.

A look at the meteorological setting shows that, even though CAPE was relatively "small" over east central and northeast KS (< 500-800 J/kg, see RUC soundings above), strong warm advection was occurring from the southwest. A comparison of NAM model temperature & moisture profiles from 6 to 9 pm near Emporia (see 4th graphic above) showed that warming and moistening was occurring in the lowest 1.5 km above ground, with cooling ongoing above that. This reduced a sharp temperature inversion that was present earlier, and changed the thermodynamic environment from "quasi-elevated" (most instability coming from air parcels originating well above ground) to one that was becoming more surface-based.

While never strongly surface-based as seen by the Emporia RUC soundings above (probably one reason the tornado was short-lived), enough low-level stability was being removed by the low-level warm advection in combination with very large low-level wind shear (storm-relative helicity over 600 m2/s2!) to sustain marginally surface-based updrafts that could briefly support a strong tornado. The fact that the parent supercell had been established for so long (3 hours) in flow of more than 80 kts aloft also likely helped the storm produce the tornado in a marginally surface-based setting. This is a reminder that long-lived supercells within a zone of strong warm advection and low-level shear should be watched carefully regarding tornado potential, even if the initial environment ahead of the warm advection looks rather "elevated" in nature.

The last graphic above shows the evolution of the surface pattern and the tornado environment (as suggested by the SPC significant tornado parameter) during the night. Tornadoes occurred in southern Missouri near Buffalo (1 death) and at Branson, and also in southern Illinois with the deadly EF4 tornado at Harrisburg before dawn. Farther north from Kansas City eastward, storms finally outran the warm advection zone and moved into a more stable environment, eventually losing their severity.

Tonight and tomorrow (March 2nd) will likely see a repeat performance of tornadoes over southern MO and northern AR into the Ohio Valley with yet another weather system. People in those areas should be on the alert!

- Jon Davies 3/1/12

Tuesday, February 21, 2012

Cold-core system on 2/20/12 - 1 dead but no tornadoes

Yesterday's cold-core system (President's Day 2/20/12) with an elongated 500 mb low crossing Nebraska didn't produce any tornadoes, but sadly caused 1 death as straight-line thunderstorm winds farther south toppled a mobile home near Ada, Oklahoma. Shawna and I, along with photographer Stephen Locke, traversed the system driving back to KC on I-70 after the Denver Storm Chaser convention, enjoying the sight of February cumulus towers and some low-intensity storms near the wind farms west of Salina, Kansas.

It's hard to get tornadoes in the Plains in February, even with cold-core systems, so our expectations were low. This system and one that produced several weak tornadoes in central Nebraska last May 12 make an interesting comparison regarding tornado potential.

From the visible satellite photos above that compare both systems at early to mid afternoon, the 2/20/12 system showed little visual evidence of a closed mid-level low (too elongated and linear), and low clouds were socked in around the south-central Nebraska surface low, limiting surface heating. In contrast, the 5/12/11 system showed easy-to-see spiraled cloud patterns around both the mid-level low and surface low, with several boundaries and plentiful sunshine evident over central and southeast Nebraska providing heating and boundary focus for storms and rotation just east of the Nebraska surface low. The elongated nature of the 2/20/12 mid-level and surface lows (compare those with the more circular patterns on the 5/12/11 SPC 500 mb & surface graphics above) could not properly bring into juxtaposition the necessary ingredients and focus for supporting tornadoes (sunshine, CAPE, well-defined boundaries, and low-level shear spiraling into the Nebraska surface low). The afternoon surface analysis above also showed a strong cold front yesterday catching up with the surface dryline over northern Kansas, squeezing off needed sunshine and surface heating over that area and southern Nebraska. Meanwhile, very cold air and energy aloft surging eastward at 700 mb around the bottom of the elongated mid-level trough over southern Kansas and Oklahoma (see last SPC image above), along with sunshine and surface heating in that same area, triggered moderate to occasionally strong linear storms over southern Kansas and central Oklahoma.

When considering tornado potential with cold-core systems, circular/spiraled mid-level and surface wind and pressure patterns win out just about every time when tornadoes do occur.

- Jon Davies 2/21/12

Thursday, February 2, 2012

Tornado forecasting classes at ChaserCon 2012

As was announced on the ChaserCon 2012 website last month, I'll be teaching 2 tornado forecasting classes on Friday evening , Feb. 17 at ChaserCon in Denver.

The first class deals with Basics (surface maps, upper air maps, and computer model forecasts, from 7:00 pm to 8:45 pm), and the 2nd class is Advanced material (including skew Ts and hodographs, from 9:00 pm to 10:45 pm). Enrollment in advance is required (you also need to be registered for ChaserCon to attend), and each class is $15.00 individually, or $25.00 for both (CASH only at the door, NO CHECKS!).

We're getting close time-wise, and class enrollments are filling up, so send an e-mail to Roger Hill at or to me directly at to enroll. Please specify which class you will be attending (Basics, Advanced, or both)

Tim Vasquez from Norman OK has taught the forecasting classes in the past. Even though he's not teaching this year, he will have a vendor table at ChaserCon to sell his forecasting books and materials, which are excellent storm chasing resources. Tim also continues to do chase forecasting classes in Norman, another great way to learn about severe weather forecasting! So if you are going to ChaserCon, stop by his vendor table and check out his stuff! Or, check out his web site at

See you at ChaserCon!

Jon Davies - 2/2/12

Monday, January 23, 2012

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

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