Texas Tornadoes of May 15, 2013

 Posted by at 3:50 pm on May 16, 2013  Storm Review  No Responses »
May 162013

Supercells Wednesday Evening Over Northern Texas

Supercells Wednesday Evening Over Northern Texas

We are all hearing about the devastation which occurred last night in northern Texas as several supercell thunderstorms produced multiple tornadoes.

At last count, six people have been killed. The communities of Granbury and Cleburne were particularly hard hit.

The Granbury-Cleburne storm was tracking to the southeast.  A thunderstorm in general will move along a path dictated by the summation of winds it experiences at all levels of the atmosphere.  Supercell storms possess internal dynamics which allow them to turn away from the prevailing winds, most often tracking slightly to the right of the path taken by other weaker storms.

What this essentially did was massively increase the low-level inflow of this storm to favor violent tornado development.

Another bizarre (but not without  precedence) development with this supercell storm was the nearly ninety degree turn to the left of the tornado toward the end of its life.   Even weather-savvy folks and those meteorologists tasked with the job of warning for this storm had to quickly correct for this movement, which ended up being a beeline for the city  of Cleburne!  If I were living in Cleburne with radar on my desktop, tracking the storm, conventional wisdom would have caused me to breathe a sigh of relief as I watched the storm track south of town on what had been a very consistent heading.

The movement of tornadoes to the left toward the end of their life was documented in the 1960’s by Dr. Fujita (F-scale tornado rating, now enhanced) and others.  Generally, it occurs as the tornado within a larger circulation called the mesocyclone begins to be guided more by that circulation and ends up hooking in front of it to the left.  This is often referred to as an occlusion of the mesocyclone. In the Ozarks, the Pierce City-Battlefield tornado of May 4, 2003 took a slight turn toward the end of its life and sealed the fate of Battlefield.

Greensburg Tornado Curled Back to the Northwest. New Tornado Just East of Town

Greensburg, KS (2007) Tornado Curled Back to the Northwest. New Tornado Just East of Town

An occlusion can mean that a new mesocyclone and tornado will form soon somewhere to the east of the old circulation.  That’s assuming the supercell is still in a favorable environment.  I chased such a multiple occlusion in Kansas in 2004, the video of that chase is included below.

It is generally true that this turn to the left is the stage before the tornado dissipates but it can certainly continue to be a powerful twister while this is happening!

Greensburg, KS had a very similar tornado “hook”, the only difference was these storms were tracking northeast. The tornado took out just about the entire town (read more) Just shift the diagram clockwise 90° and you get the same result as Cleburne, TX.

For storms like Cleburne and Greensburg, the tornadoes are so powerful that their relationship with the mesocyclone becomes a bit more fuzzy.

I included a short radar loop I recorded Wednesday evening showing the sharp left turn to the north of the tornado. In retrospect, Cleburne was lucky that the tornado dissipated as quickly as it did!

Multiple Mesocyclone Chase:

Cleburne TX Sharp Left Turn on Radar

May 092013

Outflow Area in Oklahoma at 6:30 a.m.

Outflow Area in Oklahoma at 6:30 a.m.

Lots of unstable air, an outflow boundary, a cool front and enough upper level shear should provide a stage for severe storm development over portions of Oklahoma and Texas today.

The upper air data from this morning confirms the necessary ingredients for the set-up.   There will be several possible start-up areas for storms today.

I am always wary of early development (noon-3 p.m.) and today this is possible in connection with a outflow boundary now easing into southern Oklahoma. I’d watch areas between Oklahoma City and Ardmore, OK first.

I’ll also be ready to head west quickly today to catch some storms along the dry line in southwest Oklahoma southward into Texas.

Interaction with outflows and fronts will be important for tornado potential today.  Also, patches of higher instability and careful tracking of upper level features will be necessary (if known!)

The”Lock and Load” tour leaves between 9:30 and 10:00 a.m. this morning.  We’ll be back sometime Friday afternoon.

As always, contact me if you would like to go, it is always an adventure!


May 082013

CAPE Forecast From 18z NAM Model

CAPE Forecast From 18z NAM Model

I’d say I’m about 70% in for the “Lock and Load” tour for Thursday, April 9th.

A “Lock and Load” tour is your chance to ride along with me and see some severe storms in active.

Since I’m considering southern Oklahoma and northern Texas as the chase zone, an overnight stay is required. “Lock and Load” tours leave on the day of the chase, stay overnight and then come back to Springfield the next day.

In this case, we’d leave Springfield in the 9:30-10:00 a.m. hour Thursday and come back Friday afternoon.

O.K., why the uncertainty? Well, I think we’ll have plenty of unstable air to work with but there are a few things I’d like to have “final eyes” on before I definitely decide to chase.

I have suspected all along that the computer models are not forecasting enough upper level wind with this set-up. The afternoon runs of at least one model seem to be supporting this idea. With regard to these winds, I would need to see the “truth” tomorrow morning which means what are the actual upper air wind measurements over this area tomorrow morning?  These would be widely available sometime after 8 a.m.

Then, I’m real curious about what happens with traveling areas of showers and storms tonight, many of which will likely form on the dry line in western Oklahoma. Depending on how these track, the mesoscale (small scale) could either be enhanced or diminished in some areas especially with regard to the low level wind field needed for tornadoes.

One possible target area is the dry line over Texas, say between Abilene and Childress.

There is also a weak cool front slowly sagging south through Oklahoma but here again, its position and strength will be regulated somewhat by what happens to storm and rain areas overnight and early on Thursday.

Dew Point/Wind Late on Wednesday Afternoon

Dew Point/Wind Late on Wednesday Afternoon

If you would like to go on the tour tomorrow, Thursday, May 9th, get in touch with me either on social media or by e-mailing me at: ted@tedwkeller.com

I can apply discounts the more guests I get to talk amongst yourselves!