4/28/06 FCST: TX

Aug 19, 2005
Atlanta, GA
Models now all agreeing with the ejection of the SoCal closed low into NM and west TX by Friday- details of course differ, but there should be enough oomph to this system to produce severe weather- best shot for supercells will probably be in central or south TX.

A brief review of this morning's 6z NAM tells me this:

System looks a little stacked, but maybe that will change in time. If it doesn't, there's a possible problem with upper flow around my potential target of somewhere around CDS to Snyder (for initiation). Yeah, it would be left-front exit region, but then what? Especially given the precip being progged at 0z all the way back into......hell, AZ. Scf low looks to be too weak (>1000mb), and it looks like a convective event too driven by a glancing blow from the cf. Reminds me of Monday, actually.


Time to sit and wait right now.
Still quite a few questions regarding this system. The current sat imagery shows the closed low may be starting its progged eastward turn into northern Baja- the models are still not totally on the same page regarding the exact track and speed of this feature- and this will have a huge effect on the prospects for chaseable supercells on Friday. Right now I have a feeling that this low will come out either too far south and/or too positively tilted to cause really strong surface cyclogenesis in TX during the daylight hours- and also there will be a large area of rain and cloudiness across the area of interest during the morning- which will limit the instability. My gut currently is telling me that this will be a difficult system to chase- with the best bet for discrete supercells fairly far south in west or central TX from MAF to SJT to AUS- or even south of there.
Still a lot of time for things to change- once the low gets into the radiosonde network perhaps the models will have a better handle on the situation.

I think the bulk of tomorrow's potential hinges on the degree of insolation and resultant destabilization by afternoon. If we see widespread cloudcover and precipitation across central and northern TX, like we saw last week, I don't think we'll ever realize enough CAPE to do anything with the nice shear profiles that will be in place across the area. However, if we can clear the clouds out east of the dryline (where that sets up) across Texas, I do think we could see a decent tornado potential develop. With strong flow aloft and backed low-level flow, deep-layer shear should be in the 45-65kt range. Low-level shear will also be strong across southern/central/northern TX, but the 12z NAM backs off on the degree of low-level shear along the dryline north of I20. While the maps show that, the forecast soundings do not -- For example, note that the 0z SPS sounding shows 1600 CAPE and ~240 0-1km SRH, and the 0z Abilene sounding indicates >250 0-1km SRH. Regardless, if cloud-cover doesn't clear, I don't think we'll care much about the 0-1km SRH since there'd be a significantly reduced probabilitiy of surface-based convection (with updraft source layers located above the cool, stable near-surface layer).

This morning's 12z runs (NAM, GFS, WRF/NMM) are coming into a little better agreement in the placement of the various features tomorrow, so we shall see... There's also the chance that the models are too aggresive in moisture recovery tonight and tomorrow, though the juice is just sitting in far southern TX, awaiting tonight's strong LLJ.
The 18Z MesoNAM (20 km) suggests the low pressure center to deepen into northern TX and increasing the 850 mb flow from the SW into northern and central TX from 10 knots initially to on up to 30 knots. Dryline becomes very well defined from 15-21Z at the time of convection. CAPE is shown to increase anywhere from 1000-2000 J/kg from northern TX southward along the dryline. 0-6 km bulk shear is at 75 knots ahead of the dryline in central TX (but much weaker in northern TX). 0-1 km SRH is anywhere from 50 to 100 m2/s2 while BLH is along the lines of 150-300 m2/s2 (higher values further east). I am almost somewhat concerned that the best helicities will be too far east of the dryline.

Nevertheless, the overall the precipitation pattern is for early morning forecasted convection to move off SE as a wedge of drier air entrains around the developing low by 21Z. The model suggests that clouds dissipate ahead of the developing dryline, strong bulk layer shear moves into central TX to suggest any storms will sure be spinning, strong SE flow at 15 to 20 knots places 60 to 65F dewpoints ahead of the dryline. This almost seems like the other day where a MCS was moving into SW Missouri while multiple OU people were chasing the dryline further west where it cleared out and a tornado developed at El Reno (sp?).

Anyways, anywhere from Abilene to Acuna looks really good for the development of supercells and being sustained. Later precipitation runs suggest some discreetness and then an entire squall line.

Honestly I'm just telling you what I see and I encourage any debate ... I could be too optimistic. I would simply anticipate where the moist and dry axes come together because I believe anywhere you go the helicity will be there.
Anyways, anywhere from Abilene to Acuna looks really good for the development of supercells and being sustained. Later precipitation runs suggest some discreetness and then an entire squall line.

With the dryline looking to be back in the vicinity of the caprock by firing time, Abilene will be WELL WELL east of there, the the tune of over 100 miles. I would expect to see a triple point somewhere from Plainview to Childress with a SW oriented trailing dryline, back across the south plains. The biggest concern...what will happen tonight and how much convective crap will still be around tomorrow to get in the way of heating.
With the dryline looking to be back in the vicinity of the caprock by firing time, Abilene will be WELL WELL east of there, the the tune of over 100 miles. I would expect to see a triple point somewhere from Plainview to Childress with a SW oriented trailing dryline, back across the south plains. The biggest concern...what will happen tonight and how much convective crap will still be around tomorrow to get in the way of heating.

The mesoNAM has the low pressure developed further south than Childress/Plainview. As a result of both the more southerly position of the low and the fact that the 0-6 km bulk shear is stretched more across central TX (there's a huge void across northern TX where Childress/Plainview is) I chose those places to be more supportive of sustained supercells.

Things could change, and anything is possible!

Still ... the 0-6 km bulk shear and 0-1 km helicity seems far ahead of the dryline and the concern over morning convection


EDIT: by 18Z the dryline is in the vicinity of Childress/Plainview ... but by 21Z when convection is progged the dryline seems east of that location and the greater severe threat is further south.
I'm encouraged greatly by the 18z Eta. What earlier appeared as a fairly marginal setup is showing hints of bigtime potential. The factors that grabbed my attention on the latest run are as follows:
  • Eta is hinting at a break in the action during the daylight hours (presumably) as a result of subsidence in the wake of an exiting shortwave trough. This would help increase the cap and clear out junk storms that would inhibit surface heating.
  • CAPE is progged to be somewhat higher than in past runs (CAPE ~2000 j/kg). I had a discussion with Jeff Snyder earlier today, and he pointed out that the lack of CAPE is probably due to the convective paramaterization being turned on (and the use of the MALR instead of the ELR). If convectiion were to clear out, CAPE >2500 j/kg could be realized.
  • Shear profiles continue to look awesome. Forecast hodographs are near ideal, so assuming an isolated supercell can develop with sufficient surface based instability (which, granted, is a big assumption), tornadoes would be a good bet.
Overall, this setup is looking a lot better than earlier. I've been keeping an eye on it for a while since my bro is in town from CA, so he's hoping to get in on the action. Hopefully the atmosphere wil cooperate.

I have parked for the night at Midland.

From what I have checked on the 18Z GFS run, I am thinking the region near San Angelo and perhaps further south would be ideal. Like Gabe, I too am enlightned by the latest model run with increasing moisture/CAPE.

This evening, we had stratus racing NW in the low level jet. Awesome!


Jimmy Deguara
Well, there is pretty good potential for supercell develop from far southwestern OK, southwestward into western/central Texas, as a strong upper-level low moves out of the southern NM / northwestern Mexico area. A strong low-level jet (~50-60kts on area VWPs) is currently in place across much of central Texas, which is helping to advect Gulf moisture northwestward. Convection has developed and persisted across the panhandles and eastern NM this evening.

As the low moves east-northeastward tomorrow, strong flow aloft will overspread the expanding warm sector. Widespread, isentropically-developed precipitation will likely be ongoing across much of northern TX and OK by mid-morning. Tonights 0z NAM run does indicate that there will be a break in the precipitation through 21z, after which time the model breaks out convection along the dryline. As it stands, my primary concern regarding the chase prospect tomorrow is the potential for persisten cloud-cover and precipitation across the target area, limiting destabilization and leading to poor CAPE. If this occurs, I will probably stay home, but I'll have to anticipate in the morning whether such things will persist through the afternoon. The 0z NAM does show some significant CAPE developing from near CDS southward at 21z (with SBCAPE to 3000 j/kg), but said CAPE diminishes by 0z as the model turns on convective parameterization. RH progs at 250mb and 500mb indicate that the CDS-SPS area may see some sun by afternoon, but 850mb RH remains high across much of the warm sector, indicating potential cloud-cover.

With 40+kt flow at 850mb and 700mb, 50-70kt flow at 500mb, and 110-120kt flow at 250mb, deep-layer shear profiles will be quite favorable for long-lived supercells. The 0z NAM indicated a surface low near CDS by 0z, with favorably-backed surface flow across much of the warm sector. This creates strong low-level shear, increasing to the east as one moves away from the dryline. There does appear to be a little gap between the dryline and the western edge of the strong low-level shear (0-1km SRH ~150+ m2/s2), but we'll see if that actually verifies. The backed low-level flow also helps keep storm motion in the 'favorable' range, with 25-35kt forecast motions for right-moving supercells per the Bunkers method.

I will assess the situation tomorrow morning, obviously. Right now, I'd put my chase probability at 60%. The main reason why I would not chase tomorrow would involve the anticipation of cloud-cover and precip hanging around much of the day. If this does not occur, I'll likely head southwest towards western north Texas. The NAM progs one rather significant vort max to be approaching the western north Texas area by 21z, with the leading edge of the vort max near I35 by 0z. This adds a little more complexity, since DPVA and associated upward motion would be over western north Texas in the 18-21z period, before shifting more towards I35 in the 21-23z timeframe.

I'm awaiting some 0z WRF output... All graphics are from wxcaster.com, but I moved some onto my server so I don't waste his bandwidth. Oh yeah, I do think the potential increases southward, and the area between I20 and I10 looks the hottest. However, that is likely out of range tomorrow, so I'm limiting most of my attention to the area north of I20.
Looking at the profilers this morning, the RUC's idea of more meridional flow aloft (compared to last night's NAM/eta) looks good, as does the more northward position of the surface low. So I think the shear profiles will be better this afternoon over southwestern Oklahoma, where there is the advantage of backed surface winds nearer the surface low, than in areas farther south.

The developing convection this morning appears to be in a band from Pampa to Altus to Mineral Wells, and lifting northeast, suggesting it may be forced by an approaching shortwave trough. The water vapor loop shows a traveling bulge in the upper cloud band over Texas, which hints at this. So I suspect this will get out of the way and we may even get some subsidence over SW OK/NW TX at midday, allowing some recovery. But this will be a close call, and the corridor of instability may be too narrow in the end. Deep shear vector will have a rather small angle to the dryline also complicating that target.

So ABI/SJT and southward looks like a safe bet for supercell storms, but I'm not too thrilled with the wind profiles and significant tornado potential there. The southwestern Oklahoma target is riskier with possibly higher payoff...very good wind profiles but storms that may suffer from insufficient time in the unstable air and/or destructive interference with other thunderstorms.
The 0Z sounding over Amarillo showed significant dry air intrusion aloft moreso than the models had forecasted ... morning atmospheric conditions are looking good and the dryline is setting up earlier than model anticipation. Low 60's reaching up into west/central TX.

Might be a good time to turn off pessimistic attitudes and give this scenario a look-see.
TARGET: SWEETWATER, TX TIME OF DEPARTURE: 10 AM. I expect the dryline to move east a bit today to at least the caprock. Surface moisture has rebounded nicely from yesterday. I am glad to see no convection this morning. Right now, I am looking at between SJT to Dickens with Sweetwater in the middle. Carson and I will head out I-20. Another concern is the 70 KT 500 mb flow. Too much shear and fast moving storms make for a difficult chase situation. Also, the road network is not that great just off the caprock. But we have to chase this one. Good Luck everyone. TM
My thinking is pretty similar to what I posted last night, and I'm planning on heading to CDS with a likelihood of dropping a bit south of there. I am a little concerned about the cut-off low to our west-southwest... A loop of watervapor (like this loop) seems to show that the low is re-digging, with my eyes telling me it's been moving southeast the past several hours. This may result in backed mid-upper level flow over much of the area, which would be bad. There also looks to be some agitated Cu just east of LBB right now, so elevated crap-vection may be on the increase the next couple of hours N of I20. Perhaps this will lay down an OFB, or peerhaps it'll have the same effect as the convection in nc OK on Monday or the persistent convection in N TX last Thursday (that is, re-stabilize the area and prohibit any sufficiently high surface temps).
HOPEFULY I'll get out and about today if work doesn't interfere as always. Target will be Childress. Reasoning: it's close and I like how the dryline is progged to nose into the area in the later afternoon. I won't know if I even can go until 1-1:30, but will keep fingers crossed. Everybody be careful and happy hunting today!