3/2/08 FCST: TX / OK / AR / LA / MO / IA

[Bob Schafer]

18Z WRF came in a bit weird, IMO. Nice 999mb sfc L in E NM, and then SW sfc winds from around E of LBB up to OUN? I like the 18Z GFS solution better. We'll see. I'm somewhat concerned about the CF undercutting storms, but if the sfc L is deep enough that might be prevented.

 

[Darrin Rasberry]

SPC (hopefully not stepping too far out of boundary, but in a somewhat messy report IMO) has moved the target area toward the central/south central plains of Texas. I initially was skeptical of this report, but conferring with Craig Maire I've come to believe it a bit more - the gulf moisture might light a match that could ignite Central Texas a bit more than the North Texas region.

Also of concern: I wonder how fast the cold front is moving now. I don't have access to all of the non SPC models, so I'm currently unaware on whether the projected low is enough to put the breaks on the front - a very present possibility that could push all the possible supercell setups into a squall line soup, as well as the SPC's stated potential mitigation from cloud cover sapping heat from the area on this day.

 

[Genaro Estrada]

I'm putting my money on SE to Central Texas, and SE Oklahoma. This is where the moist tongue and dewpts in the 60s will be in place, and this area will be just ahead of that digging trough, along with the right entrance region of the jet stream, and associated divergance. Severe Wx will then push eastward to over Lousianna, Southern Arkansas, and Georgia by Tuesday.

 

[Bob Hartig]

WRF shows a decent area of 1,000 CAPE south of DFW and dewpoints from the mid-fifties to sixty. Southerly surface and 850mb flow. But while there's progressive veering with height, there's nothing in the way of 1-k helicity, and I don't see much mid- and upper-level support. If I lived in Dallas, I'd be keeping tabs on things, but when it comes to making the drive from Michigan, I think I'll save my shekels for something more compelling.

 

[Michael O'Keeffe]

Just saw the latest models, the WRF looks pretty bad, but the GFS looks really good. The LLJ looks great as well as the 500mbs across C Texas, the dryline looks very sharp with 55F tds dropping to the 30s very quickly across NW down into SW TX. A 997mb low is in place in NW Texas just W of Wichita Falls. As of now I am hoping the GFS verifies because we could surely see some tornadoes if that verifies. I'd target the dryline from the double point near the Red River south to I20.

 

[Chris Wilburn]

I agree that the NAM/ETA looks like a mess, but the GFS looks really good. I like the fact that the GFS tightens up the dryline much more than the NAM. Dewpoints near 60 and SBCAPE of 1,000-1,500 should be in place along with really nice shear profiles and a deep low of 997mb in the NW TX vicinity. I did notice that by 00z there is still some CINH left to be eroded in NW TX so that may be an issue. If the GFS verifies this could be a really nice chase day with some tornadoes. The key will be a manageable CAP and getting storms to fire off the dryline and get far enough ahead of the cold front to keep from getting undercut. I guess it is just a matter of which model is more reliable at this point. It will be interesting if over the next 24 hours or so if the GFS and NAM/ETA can come into agreement. Right now I would target anywhere from Wichita Falls down to I-20 with further south being more of a prime area.

 

[Simon Brewer]

Well, made a quick forecast for Sunday looking at 0z- 3/1/08 UPA data from tonight and 0z WRF and GFS forecast runs and TX sfc map:

Looks like the possibility of supercells across TX on Sunday is totally determined by the compact closed-low/short-wave currently off the coast of Southern Cal., which is forecast to be 'kicked' into the westerlies by a larger shortwave digging into the west coast of Oregon and Washington.

If the WRF and GFS UPA forecasts verify, then I would expect supercells to develop along the dryline in West TX between Abilene and Sonora late afternoon on Sunday. Modified gulf moisture under relatively steep lapse rates along with significant daytime heating ahead of the dryline should provide adequate CAPE values in that region. CAP should be strong early in the day with southwesterly 850 and 700mb winds, but low and mid-level cooling associated with that compact shortwave (diff-vort-advection) should weaken and break CAP along the dryline by late afternoon/early evening. I don't really like further north in Oklahoma and Southern TX Panhandle, unless you want to guarantee seeing a t-storm as the cold front plows south and forces and elevated squall-line. The pressure falls along and ahead of the cold front should weaken convergence along the dryline north of I-20, so I would not expect storms to develop along the dryline north or northwest of Abilene.
This is just my forecast using some data available on the night of Feb 29th, so WRF and GFS forecasts will likely change. Hopefully the southern compact shortwave does not slow down, which means the elevated cold front squall line will be the main show.

Simon

 

[Shane Young]

My 2 cents

Looks like the earlier shortwave will be out into Texas by morning...

I actually think that's beneficial, as the residual subsidence could hold down convection during mid afternoon under a weakening cap... so that you could then see some very spectacular development just before dark along the dryline in Texas.

Or it could hold things off until it's too dark.
I'm not seeing the big concern, though, with undercutting, except perhaps in the TX Panhandle at the triple point. Perhaps it looked worse in earlier model runs.
Looks like the interest is the dryline mostly tomorrow where there'll be better moisture and far removed from the cold front. If I had any options, I'd want to be setting up between Childress and San Angelo/Sonora by tomorrow afternoon.

I'd be most worried whether the storms could really erupt before sunset... and whether the winds aloft would make it in enough to provide better helicity.


But that's just me

 

[Simon Brewer]

Whoa! Just caught a look at tonights (3.1.08) 0z WRF forecast and man does it look drastically different from previous forecast runs. Like Shane said, the smaller compact shortwave rapidly ejects across TX and OK early Sunday and then the big shortwave closes off, slows down, and sets up two nice looking days; sunday across NW TX/OK and then Eastern AR on Monday!

Concerned UPA support along dryline for Sunday, but if a nice clear slot situation unfolds across NW TX and SW OK then it could be big with the surging cold front being a 'big gorilla' that could mess up the whole setup.

Monday won't be pretty, but tornado chances are incredible across AR and Western TN.

Simon

 

[Matt Chatelain]

Looking at the new 0z wrf shows an interesting setup for tomorrow. Seems that the models continue to show the cold front not making as much of a push south as it is just coming into nw oklahoma by 0z. The dryline is well defined with a nice bulge near the front. Surface low now forecast to be at 993mb at 0z, which is nicely backing the winds near the low (from clinton to altus). Only questions remain is instability and convergence near the dryline. But if a surface based storm can fire off the boundary it could be fascinating. At 850mb there seems to be nearly pure convergence at the front. Can't wait to chase near home. Would love to see a system like this in May, hope this is a sign of things to come.

Also of note... a lot of snow possible tomorrow night for some.

 

[Bill Schintler]

Chase Target for Sunday, 3/02/08

Chase target:
Snyder, OK (between Altus and Lawton).

Timing and summary:
Storms will develop rapidly between 3 and 4 PM CST. A few supercell storms will be likely early in the convective evolution before a transition one or more multicell clusters and/or lines takes place with the approach of the cold front. Large hail to golf-ball size will be the primary severe threat with the discrete storms.

Synopsis:
ULVL charts and WV imagery showed a number of compact disturbances embedded within the SRN stream of the WRN CONUS trough, the most significant of which was a potent vort max in SCNTRL AZ. At the SFC, a diffuse trough axis extended from low pressure centered near DEN SWRD S to CDS. In TX and OK, winds were backed E of this feature, and this will set the stage for moisture return overnight. Dewpoints AOA 50F remained E of an SRB to ABI line in TX, and deeper moisture will push slowly WWRD overnight. Taking a look at soundings, steep lapse rates from the SFC through 600mb were noted over AZ and NM.

Discussion:
There will be two regions of consideration for convection on Sunday. Storms are certain along a strong CF by early afternoon in NWRN OK into the NRN TX panhandle. Moisture and SFC-based instability will be limited with these storms, most of which will be post-frontal and undercut by cool air. Furthermore, wind fields will be veered, uniform, and unidirectional and no further consideration will be given to this area as a viable chase target.

A second area of interest exists further S for conditional discrete convection. A sharp DL should provide the focus for convection as the left-exit region of a compact H5 vort max and 70kt jetlet rounds the base of the trough. A N/S axis of CI associated with this feature will push E through the TX panhandle in the morning and reach the WRN OK border by 17Z. This lead wave will push E during the mid-afternoon hours and will be followed by a second, stronger 95kt jet that will round the trough base and approach the area, providing for a broad region of UVM along the Red River by late afternoon. Capping is a concern; however localized dynamic forcing along with mid-level cooling of several degrees will erode the CIN by mid afternoon. A ST shield along and E of a Clinton, OK to Wichita Falls, TX line will also begin to move E, allowing a narrow axis of insolation in the most sector. SFC low pressure will strengthen and sink S towards CDS during the afternoon in response to differential heating and CAA behind the CF, and SFC flow will back in response in SWRN OK. Forcing and UVV’s will increase rapidly and the DL will mix out and surge E/NE. E of this feature, SFC dewpoints of 55-60F beneath steep mid-level lapse rates of 8C/km will contribute towards MLCAPEs of 1000J/kg within a narrow instability axis. Deep-layer sheer vectors of 50kts (SFC-6km) and moderate SFC-3km hodographs will aid in storm organization.

- bill
[FONT=&quot]10:00 PM, 03/01/08[/FONT]

 

[Jeff Piotrowski]

Sunday & Monday

I would expect nice storms based on the new 0Z ETAKF for SW OK on Sunday afternoon ahead of dryline and surface low and backed winds.

The upper low moves across North Texas on Monday setting the stage for heavy snow potential for eastern Oklahoma/NW Arkansas/SW Missouri. The new data suggest thunder snow likely with totals in excess of 12"+ near the I-44 corridor.

I would also expect a severe weather in LA,AR,TN,,AL, on Monday!

 

[Jason Montano]

I am really liking the setup for tomorrow after looking the the 0z model runs. The ETA and GFS are nearly in agreeance except for some slight differentiation on the lows position. I think the triple/double point that will be around NW TX / SW OK will be a great area. The ETA has the Cap holding until late afternoon in that area allowing CAPE to build to 1000-1500. There is also nice upper level support. I am going to see what the soundings look like in the morning and make a chase/no chase decision then. However, as of now I think NW TX could be the place to be tomorrow.

 

[Jason Boggs]

ETA looks to be slowing the cold front down. It puts it along the central TX panhandle by late afternoon. I don't think I will waste my time playing with the cold front, even though storms are pretty much guaranteed to fire on the convergence along the front.

Therefore, I think I'm going to play a little further south away from the cold front along the dryline and near the shortwave that will be approaching. The area that I'm interested it at this time is the area in SW OK near the Altus or Lawton area. My reasoning for picking this area is to stay away from all the mess along the front and hope a few isolated storms fire further south along the dryline and approaching shortwave energy. I'm also hoping that this south target may be in the clearing, so hopefully a little more daytime heating may ensue.

I think cloud cover due to the approaching shortwave may inhibit daytime heating somewhat, especially the further north you are. Daytime temps in SW OK should be near 70, and I think dewpoints should approach the mid 50's. With these factors at hand, I think the instability will be descent for this time of year with CAPE around 1,000 j/kg. Shear will be pretty favorable for supercells, especially later in the period, around 3-6Z. Finally, backed surface winds will enhance helicity values NE of the low in SW Oklahoma. Good luck to all who venture out tomorrow. If you happen to be in SW Oklahoma and see a yellow Nissan Frontier, stop and say hi.

 

[Chris Wilburn]

I just looked at the 00z ETA as well and agree mostly with what has been previously said. Things are looking very nice for SW OK/NW TX. Very nice deep low and nicely backed winds forecasted for extreme SW OK into NW TX. Helicity values are also very impressive along with 1,000-1,500 forecasted CAPE and dewpoints near 60. I think further into NW TX may be a bit better than SW OK as it should be a bit longer before the cold front undercuts storms down there as opposed to SW OK, but it will be a narrow window. Any storm that can fire off the dryline and become surface based and stay ahead just enough of the cold front has a chance to be a really nice storm. Tornado potential is there for sure along with large hail. As the cold front quickly moves through it should be a nice MCS plowing through OK the remainder of the evening into overnight. I am thinking about heading towards SW OK tomorrow morning. This will give me time to make it back to where I live (NE OK) to catch the snow event. I just looked at the snowfall amounts predicted that Jeff mentioned and it looks like portions of NE OK into eastern OK could get a significant amount of snow anywhere from 6"-12". This is just a model projection so take it what it's worth, but the potential is there. As of right now I would target a line ahead of the dryline from extreme SW OK into NW TX. Snyder, OK looks like a nice spots that was previously mentioned in this thread down to say Wichita Falls, TX and points south. It will be interesting to see what the RUC has to say in the morning and go from there.