2/16/08 FCST: TX/LA

[Bill Schintler]

Chase Target for Saturday, February 16

Chase target:
Canton, TX (I-20 mile marker 526)

Timing and storm mode:
Renewed development of surface-based storms will occur by 2 PM CST. A full spectrum of severe weather is likely over a large portion of eastern TX south of I-20, including violent and long-track tornadoes.

Synopsis:
ULVL low was sinking SW towards SRN AZ, and a lead wave has rounded the trough base with stronger H5 flow now spreading towards TX. Locally, A CF had pushed S to a Shreveport to Austin to San Antonio line, while a H9-H8 SRLY LLJ was increasing NWRD WAA and moisture transport aloft. Convection was ongoing, owing to isentropic upglide along the 290-305K SFCS and MUCAPEs of 500-1000J/kg. FWD, AMA, and MAF soundings indicated a deep moist layer and steep lapse rates above a cold and shallow post-frontal air mass.

Discussion:
Elevated convection will likely be ongoing along and N of I-20 early in the period.
Widespread ST and mid-level cloudiness will blanket most of ERN TX through the mid-morning hours. Later, an area of partial clearing of the low-clouds will take place through the noon hour, allowing for a period of destabilization S of I-20 and E of the Dallas area. The most favorable location for discrete storms and supercells will be along the WF just E of the SFC low. Linear development will also occur along the CF as it pushes E into the axis of instability.

Modest instability will couple with very impressive shear, hodograph curvatures, very strong flow just above the SFC, and low LCL levels to create an environment supportive of rotating updrafts and tornadoes. Dewpoints in the 60-65F range beneath mid-level lapse rates of 8-8.5C will contribute to MLCAPEs in excess of 1000J/kg. A SFC WF will intensify along I-20 on Saturday. LLVL shear will be enhanced along and just N of the boundary. A 60kt SRLY LLJ surging over backed SFC flow will contribute to large hodograph curvatures with (SFC-2km) SRH in excess of 500m2/s2. Deep-layer shear (SFC-6kg) will easily exceed 60 kts in the exit region of an 80kt H5 streak.

- bill
[FONT=&quot]10:00 PM, Friday, February 15, 2008[/FONT]

 

[Matt Grantham]

Myself and 2 other meteorology students from the University of South Alabama in Mobile are targetting the area near La Grange, TX tomorrow. This area looks like it will have the best combination of instability and potential for discrete storms.

Good luck to everyone tomorrow.

 

[Bill Tabor]

I agree La Grange is probably a reasonable target, perhaps also the area se of San Marcus 18zish near Seguin. I was expecting the breakout from 18z to 21z and some of the things I looked at seem to indicate and concur with that; however http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/cent4km/v2/tcolc_f24.gif seems to show that a squall / wave begins to develop on the south end as the vortmax approaches then boom supercells extend down the line closer to 23z or 0z (i.e. dark). It then continues in the dark. That seems odd to me as the dynamic forces will be out in force starting 12z likely with intense overhead 850mb jet by 18z over central Tx. If this convective precip forecast is true that could be real tough for chasers trying to see things, and worse for public in the path. As intense as the lower and upper jets are I'm surprised to see many of the composite indices not showing off the scale. Not sure why that is - certainly it will be cold aloft with mucho instability. My inclination is this will be one of those days with fairly poor visibility and numerous storms early on. The upper level disturbance, and low level jets will coincide to produce fairly fast moving, possibly intense / destructive tornadoes. Time will tell, but I will try and be watching it early, if not off and on all night as the battle begins and the front lines approach. The truck is ready and the powder is dry.

 

[Darrin Rasberry]

My dice were originally on Giddings earlier today, but the current garbage around and east of the I-35 corridor in the Austin/San Antonio area might suck the blood out of the early afternoon if they last too long.

Should I have chased this event, I might have decided to move south down the road to Victoria, possibly east a little bit to El Campo or maybe even Palacios should storms have a slower track; the roads and viewing around that area are remarkable all the way to Lake Jackson if the oceanfront area ends up at least slightly better than a bathroom at the end of a hot shower.

 

[Mitchell Daszewski]

Cold front has pushed pretty far south and east overnight but has now slowed up to near Brenham. Surface low taking shape near Cotulla Texas. RUC depicts a good caping inversion over southeast Texas this afternoon with a saturated layer below that. Question is whether any of the low level clouds break up for sun to peak through to provide added heating and instability. If not, then I think chances for prefrontal surface based storms will be low near the Houston area, so we'll watch an intense squall line develop.

I will drive west of Houston down I-10 and watch how things play out...should be fun either way.

 

[Bill Tabor]

Looking at this morning's data and models it appears to me that the front has gone a bit further south and east than one (such as myself in AUS) would like to see for local chasing in decent terrain and road networks. For tornadoes I'd have to say I pretty well concur with SPC's moderate area. Both RUC and NAM seem to show limited recovery of warm sector closer to AUS during the day. By 18z or 19z dewpoints are shown to begin eroding in western parts of south Tx as the approaching jets move into the area and interact with the area ne of the low in south Tx. The low appears to elongate N/S some and much activity seems to move east and somewhat north as is typical this time of year with this type of system. I still see an area of interest se of AUS say 70 to 100 miles or so that is northeast of the low by 18z or 19z and should begin to see some interaction with the low level jet and the 700mb jet. It appears the area of upper level lift is still to the west of a n/s line thru AUS and is approching. It may be a few hours though before that moves in. So, perhaps by 21z the upper level dynamics may begin interacting with the boundary and warmer air.

Likely there will be a few tornadoes some, strong. Many will be further east and southeast than I care to go. HOU locale may find some interest nearer 0z. However overall I'd say the threat is less for daytime good terrain tornado chasing in Tx than I appeared to be the case on previous days / earlier runs. Probably still a decent chance for some torns further south near coastal plains and towards east TX/LA into the pine woods, with concerns after dark for public obviously particularly along maximized area of instability interacting with upper level system.

I may sit this one out. I'll be monitoring for now, but it just doesn't look too good chase wise to me given what I'm seeing.

 

[Jim Bishop]

Well I think Bill pretty much covered it - nice discussion. Seems the cold pool pushed further south and east than forecast. Over the last couple hours it has finally retreated a couple counties west and north. But this has aided in more warm air advection precip and cloud cover over Southeast Texas. In addition the cap is much stronger than forecast.

There's still a chance for some discrete cells to form off of warm air advection and become surface based in the warm sector basically in the region west of houston and east of La Grange. Any that do form have tornado potential. But the more likely scenario seems to be a squall line forming along the front late this afternoon/evening.

If things look more promising in the next few hours I"ll head west on I-10 and see what happens.

 

[Mikey Gribble]

If I were chasing I would be setting up by Victoria for now. I think the area between Victoria and La Grange will be the best shot for tornadoes this afternoon. I just got home and started my forecasting though. I really don't like all the crap over the warm sector. Aside from this being a convective mess (as expected) it doesn't look too bad for February. I don't remember a whole lot of days that were this sloppy and still came through with a good tornado outbreak.