2014-11-22 FCST: South-Central Texas

[James Gustina]

12Z NAM for this morning is still rolling in but this day is finally within a reasonable range to make a forecast thread about. Right now, it's looking like the quasi-stationary front kind of wobbling southward will begin rocketing north Friday night into Saturday through N Texas in advance of really strong moisture advection out of the GOM. Mid-upper 60s dews are being progged from the Gulf Coast all the way up to north of Dallas along the Red River in advance of a very compact, neutral shortwave ejecting out ahead of the main longwave energy. South-central Texas is looking like it'll be directly under the best upper-level diffluence as the trough shoots out over the Rio Grande towards the MS River Valley.

The shear environment has been looking great, with ~25 knots 0-1km shear and strong deep-layer shear around 45 knots coupled with decent storm-relative anvil level winds around 30 knots. The issue is due southerly H5 winds could spell issues for ventilation down the road but I feel like storms will be more affected by the saturated profiles the day of than the winds aloft. The biggest pitfall is not surprisingly instability, with the main instability axis being somewhat displaced from the best shear. MLCAPE values around 1000 j/kg and a bit higher are still being progged south of Waco near the best shear but further north it looks like contamination from the previous day's convection will temper surface temps and prevent meaningful diabatic heating from occurring.

Semi-discrete supercells near Austin looks like a possibility if everything above goes to plan with a window for some tornadoes but I'm also still concerned that the skinny profiles being shown are gonna really limit this event.

 

[Bob Schafer]

This caught me by surprise. Thanks for the heads up, James. I don't monitor the convective outlooks or the models this time of year, but I could chase this if I wanted.

That said, the first thing I always do when evaluating a forecast is to look for "problems", and there's one glaring problem here, which is the lack of inhibition. If you look at the 18Z run from this afternoon you'll see a pretty-much total lack of any cap going back to early in the day, and in fact widespread precip throughout the whole risk area all day long. In other words, garbage. Oh, well. Good luck to anyone who does chase it.

 

[James Gustina]

That's been a huge monkey wrench thrown in since it popped up. If the day before actually goes off then this day is doomed before it gets started. If the cap holds the day before I feel a bit more confident about it.

 

[Marcus Diaz]

Although, this setup does have a wide open cap most of the day, the NAM seems to be clearing out the precip somewhat early enough to get some atmosphere recovery. Looks as though if you're going to chase Saturday, you better be way south...definitely south of I-10. The forcing is getting in a little later than I'd like to see, but it's coming in hot. 0z NAM is breaking isolated pockets of heavy precip during the mid afternoon, which may be some isolated supercells near SAT (San Antonio). Looks like the messy line will fire roughly around 0z out west of SAT/AUS. Some of the high res precip models are showing healthy blips in and around SAT at 21z. Relatively large clockwise hodographs can be found around the I-35 corridor north and south of SAT. This looks like a solid enough reason to make a weekend trip down south. Probably leaving after work tomorrow and staying the night around SAT and going from there. To be honest the tornado chances are somewhat slim. But hey, what can I say? I'm a sucker for reasonable Fall setups. At least I can calm my SDS for a little bit.

 

[James Gustina]

I'm very much on the not going side of the fence. I'm not up for a drive to SA this late in the season when I'm running low on funds and just have had terrible luck this entire year. I'd still guess that semi-discrete supercells will go up just west of SA and maybe put out a tube or two given how great the low-level winds are. Good luck to anyone that goes out.

 

[Kelton Halbert]

Yeah, I'm not planning on acting on this. This is not the sort of profile I want to be chasing.
The entire thing is essentially moist adiabatic so environmental lapse rates are crap. The wind profile might squeeze out spinups here and there, but nothing I want to spend a few tanks of gas on to see.

 

[Marcus Diaz]

Well I'm down here in Junction, TX for the night. I'm initially targeting the area between Uvalde and Laredo. I'm thinking this area might clear out in time to get some rapid destabilization around mid afternoon when the main chunk of energy comes out of Mexico. A better forecast later but for now, these are my thoughts.

 

[Marcus Diaz]

So the biggest concern is how this system slowed down. The main energy seems to be rounding just south of the border today. The HRRR does at least break storms out with robust updrafts in Mexico near Del Rio around 21z. This being on the exit region of the low might help out the day, especially with at least modest instibility and somewhat upslope flow might keep some supercells alive. The 850s are pitiful sadly. The big cell of the day looks to be south of the border. To everyone's surprise, this day is looking mediocre. Crazy I know. I'll work with what I have today, with the target looking like Uvalde, TX.