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4/20/06 FCST: TX

Jason A.C. Brock

Thought id open this up due to the fact it looks as if a decent chase day could be possible for parts of West and Southwest Texas. Abiliene over towards Lubbock and then South to Midland/Odessa area then SE towards Fort Stockton Texas. I could see a good setup for a dryline and Warm Front intersection in this area along with possible outflow boundaries from any storms that fire this evening and overnight.
These boundaries and the dryline added with some OK dewpoints and a little surface heating could prove to even set the stage for a couple tornadic cells. The activity will likely congeal into an elevated MCS and Move accross Central and North Central Texas over night but become more elevated producing a marginally severe hail threat but provide some lightning photography chances for areas such as Austin up towards Wichita Falls and over towards Dallas.
I actually hope this setup occurs a tad further North than forecast because this area needs the rain badly and id also like to get some chaseable storms in this area for maybe only the second time this year. Not tryin to be greedy guys but WE HAVE TO HAVE SOME RAIN DOWN HERE BEFORE SUMMER. If not we will be in SERIOUS trouble. We are already 3 inches below normal for rainfall for the year and we usually see 4.5 inches in April and over 5 in May. After that our rainfall stops until October for the most part.
Below is a part of the afternoon AFD out of Midland/Odessa on 4/18/06


KINEMATIC AND THERMODYNAMIC PARAMETERS APPEAR TO FAVOR
SUPERCELLS...AND WHILE IT`S A BIT PREMATURE TO ASSESS
TORNADOGENIC POTENTIAL...THE FORECAST OF A LOW LEVEL BOUNDARY
MORE OR LESS PARALLEL TO THE MEAN SR FLOW AUGMENTED BY COLD POOLS
LEFT OVER FROM EARLIER CONVECTION WOULD INCREASE THIS POTENTIAL.
SURFACE TEMPERATURE/DEWPOINT SPREADS LOOK A LITTLE HIGH AT THIS
TIME...HOWEVER...AND WE`LL NEED TO WAIT AND SEE ABOUT THE QUALITY
OF LOW LEVEL MOISTURE RETURN.


Any thoughts?

BTW there are some impressive dewpoints just South and SE of the mentioned area. Of course it depends where when if and how far the front will move northward.
 
I am lukewarm about tomorrow, but that will quickly turn to a "I like it!" if we can get the warm front to move farther north (north of I20). As it stands now, flow aloft will strengthen through the day as a shortwave approaches from New Mexico. Surface pressures will fall ahead of this shortwave, which may help draw the moisture and warmth northward into northern TX. As it stands now, stratiform / pre-WF precip may keep temperatures (and resultant instability) on the low side north of the front (north of I20 essentiall). However, winds will be very backed ahead of that warm front (easterly for most of N TX), with 20-25kt SE 850mb winds, 25-40kts SW 700mb winds, 45-55kt SW 500mb flow, and 65-75kt SW 250mb flow. In other words, deep-layer (60-70kts) and low-level shear (250-450m2/s2 0-3km SRH, peaking over 600 m2/s2 NNW of Fort Worth TX) will be quite supportive of supercells and tornadoes. I think if we can keep clouds away from the pre-WF area and let that area bake during the afternoon, enough instability may develop to suppot a tornadic supercell threat. Of course, if clouds and precip sock that area in, CAPE and supercell potential will be quite low.

So, I'll be keeping an eye on the forecast and crossing my fingers that we can bake along and just north of that frontal zone.

EDIT: Changed I30 to I20 (doh!)
 
Well, the forecast trend appears to be the exact opposite of what I was wishing for... The latest 0z runs of the NAM and RUC indicate that the warm front (currently from just east of Del Rio to near Waco to Texarkana) will move only very slowly northward overnight. With persistent convection and cloudcover on the cool side, it doesn't look like we'll destabilize enough for a tornadic supercell threat in northern TX. In absense of strong pressure falls in western TX to help bring the front northward, it appears that the main target zone will like along and south of I20, where significant directional shear in the low-levels will be colocated with 55-70kts deep-layer shear and ~2000 CAPE by late afternoon. Now, IF convection north of the warm front can stay more sparse overnight, there is a chance that the warm front will slide farther north. However, that doesn't appear to be very likely, and I see that the DFW / FWD office just issue a flash flood watch for northern TX in light of the likely probability of peristent convection. Since I don't want to drive down to San Angelo, I'll sit this one out unless (a) significant diabatic heating can occur on the cool side of the WF (across northern TX) or (B) the WF can surge northward to near or north of I20 (from the DFW area on westward). The forecast sounding for ABI tomorrow at 0z doesn't look too shabby, however --> http://www.wxcaster.com/etaskewts.php3?mod...&STATIONID=KABI

I guess I can keep my fingers crossed for a nice-looking setup on Monday... Too bad it's the 132hr GFS forecast, but at least it looks like a relatively classic sfc low setup for western OK. But, that's for another thread as the threat nears...
 
Amazing how target areas can shift in 24 hours. Things aren't looking too bad between Del Rio & San Antonio. A shortwave will move through at region today. An outflow boundary, oriented generally east-west, sits just south of San Antonio, west to near Del Rio, and east through Victoria. Any descrete supercells that can injest vorticity along that boundary stands a decent shot of producing a tornado. I'm at work and trying to find a way to leave early if conditions continue to look good through the morning.
 
Looks like overnight storms have pushed the target area to the S towards Del Rio then over towards San Antonio. You may still want to head West or SW and the tornadp threat is not that bad. As for me ill save my gase for closer probabilities and better chase terrain. I will be keeping an eye on the Wichita Falls area but only can see the chance of large hail type elevated storms here today and this evening.

good luck to those going out

Jason

KE5HZA
 
Well....what had looked to be a basic dryline/warmfront setup has become quite complicated with all the overnight and early morning convection. My initial target last night was San Angelo, TX. This morning I made a run up to Junction City, TX where I am sitting now. After looking at the latest model data, especially the RUC which seems to be picking up on the outflow boundary W and S of San Antonio I am thinking a target west of San Antonio as Jim mentioned may be the best place to be if the RUC verifies. This sounding out of Hondo:

http://www.wxcaster.com/ruc2skewt.php3?mod...&STATIONID=khdo

at 00z shows incredible low level moisture and low level shear. Good luck to anyone out and about today.

Dan
 
Yeah, this is a rather complicated setup. One thing I'm not liking right now is the low level cloud deck that isn't mixing out. The southeasterly flow at 850mb will only increase this afternoon, so I'm not sure if that cloud deck will completely mix out. Plus the initial (and stronger, mind you ) vort max is currently upon that region, which will only aid in further cloud development.

Also, with all that upslope flow from the surface to 850mb bumping up agains the Mexican Plateua, it seems more likely storms will fire off of upslope near or south/southwest of Del Rio and track east or northeast. Storms could form along the outflow boundary, but it seems less likely - upslope flow is a much better lifting mechanism. Also the orientation of the outflow boundary seems to have slipped more northwest/southeast south of San Antonio, which isn't as good as east/west.

If enough CAPE can become established once storms fire, then an interaction with that outflow boundary could prove to be rewording to a chaser! Watch that cloud deck! Southwest of San Antonio & Southeast of Del Rio appears to be the most favorable target region.
 
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