2/1/2006 FCST: South/South East Texas

Not really a daytime chase opportunity, but thought I'd point out there is slight potential this Wednesday evening / night in south and southeast Tx primarily as NAM forecasts a short wave passing far south into Tx overnight. It should be pointed out GFS shows this feature further north and faster than the NAM. Additionally this wave should be supported with small low down in Mexico and return flow moisture with dewpoints in south Tx and along the Gulf of 55F to 60F. Other winds are supportive of supercell potential and maybe a tornado if enough instability can be generated. Right now doesn't look to be a lot of instability, but NAM does show precip breakout overnight in/near these areas.

Might be good for some nighttime lightning photography.
 
This setup looks like it could certainly produce a few severe weather events across the near-Gulf region of Texas and Louisiana through 06Z Thursday. First...of note is an SPC Slight Risk over this area with a small region of 25% combined probability of severe weather.

Potent vorticity maximum (35-37 units) will track from near the Big Bend/Edwards Plateau region of Southwest Texas in the early morning into Southeast Texas by the evening hours. As the shortwave progresses east, it should begin to exhibit a transition from positive to negative tilt. Strong upper level flow will wrap cyclonically around the shortwave and this should enhance difluent flow out ahead of the vorticity maximum. In addition a surface low should develop in response to the upper level dynamics and track through South Texas. All factors point to excellent vertical motion to trigger thunderstorm development, particularly after 2PM to 4PM CST when CINH should be mostly eroded.

Moisture, always a concern in the early months of a season, appears as though it should be abundant in the severe weather risk area close to the Gulf of Mexico. A tongue of low to mid 60s dewpoints should extend north from the Gulf into Southeast Texas and Western and Southern Louisiana by afternoon. The GFS remains relatively cloud free for the morning hours of destabilization but the NAM generates a fairly deep cloud layer over much of Texas, most likely in response to the more organized low pressure system approaching. Could see some fair amounts of cloud cover and convective contamination across portions of Eastern Texas through the morning and early afternoon hours, although both models exhibit fairly dry air in place. I am going to operate under the assumption that Texas should see at least some cloud cover while Louisiana should remain relatively cloud free. In any event, even if full destabilization isn't realized, I'm thinking MLCAPE values of 700-1100 j/kg are still reasonably plausible across Texas and 800-1400 j/kg in Louisiana.

The thermodynamic environment should be marginally favorable for severe weather at best, but this will be augmented by favorable dynamics including strong bulk wind shear on the order of 45-60 knots. Expecting storms in the early to mid afternoon to initiate with the approach of stronger upper level support from the Big Bend/Hill Country of Texas eastward to the Louisiana border and then continue to intensify through the afternoon as diurnal heating maximizes instability in conjunction with the shortwave transition to negative tilt. Shear profiles over the Hill Country will be weaker with the upper level low directly overhead. Northwesterly winds could advect in drier air and induce a bit of an inversion which would make storms a bit more elevated in Central Texas. However given the strong upper level support and marginal instability, could not rule out a few severe hailers. Experimental hail prediction chart that we use at WiscWx (with solid results) yields hail mainly in the penny to quarter (0.75 to 1.00 inch) range.

More of a concern out to the east across Southeast Texas and into Louisiana with increased instability and storms more likely to be rooted from the near-surface layers. NAM 0-3km AGL layer SRH is about 150-250 m**2/s**2 with the bulk of this in the 0-1km layer. As the low deepens, surface wind vectors should back with time lending for more richly curved hodographs across extreme Eastern Texas and Louisiana by evening. Thus, prind that we could see some rotating supercells across East Texas and West Louisiana before the deepening low pressure system saturates the area with hefty vertical motion fields and cell mergers take place...lending for more of an MCC structure. Best shot for chasers IMO is to setup in Eastern Texas somewhere between Lufkin and Bryan TX where timing will tend to be on your side (concerning both nightfall and storm evolution). Hail prediction chart favors up to 1.25 inch diameter hail, but this could be augmented up to 1.75 inch diameter hail by stronger mesocyclones. BLEP equation gives max surface gusts around 65 MPH and max rotational winds around 90 MPH or an EF-1 tornado.

So weak tornadoes, modest hail and some marginally severe winds from supercells transitioning to MCC is the main story. Overall surface low doesn't seem strong enough for any major severe weather outbreak but it could get interesting and someone could bag a nader. Wow...that got a lot longer than I thought it would. :lol:
 
Interesting how we have the dance of the models once again. So now it is supposedly no longer a night event, but instead the sfc low is forming in south central Tx and the area of mid level vort is cutting right through south Tx - per NAM. There appears to actually be potential synchronization between the low level and mid level features. NAM claims 55 to 60F dewpoints will make it up off the coast and somewhat into central and southeast Tx though probably most decent air will remain near the coast. I'm not even sure how much I believe that since the current dewpoints are only in the 40's along the coast and 30's further inland into central Tx. That's pretty low. Will there be enough saturation for decent storms? Assuming some moisture - for some reason Wharton comes to mind for a target near 18z tomorrow.

If NAM verifies and sync of mid and low systems and enough moisture (55 to 60 in spots) winds seem reasonable to support some rotating storms. Perhaps near the coast a tornado is a possibility. The area between Port Lavaca and Houston has my interest along with the area just northwest toward SAT and also inland north of there perhaps 4 or 5 counties.
 
1/31 12Z ETA valid 2/1 18Z shows a LI bullseye of over -7 just southwest of the Houston area, with CAPE aoa 1500 for the same area. I'm guessing there will be alot of WAA grunge along the warm front thats progged to be just north of the area at 18Z. If that's the case, it may be areas farther east towards Beaumont that end up being far enough south of the grunge by late in the afternoon/early evening to be in some sunlight.

Updated 9:20pm EST 2/1: 00Z ETA output for 18Z Wednesday is almost identical to that of the 12Z run, still predicting 1000-1500 J/kg CAPE and LI's under -4 southwest of Houston. The same area is also just NE of the surface low. I agree with Bill, Wharton looks like a good target.
 
I would head a little north and east of Wharton...for the following reasons. I think that if I were chasing I would want to stay pretty close to the LA border to hang out of any potential cloud cover. I also think winds will back more severely up in that neck of the woods, and by late afternoon the bulk of the strongest shear will be concentrated here. This should also bear the brunt of the PVA as the vort becomes negatively tilted and begins to lift out. IDK about chase territory, but I would still tend to favor an area triangulated by Houston, Beaumont and Lufkin...more on the western edge to catch the late afternoon storms and ride em east.
 
After reviewing 0Z run my conclusions and area are similar to before; however note the following changes.

Previous it appeared the low / cold front & warm front would sync well. Now, it appears that the midlevel short wave is a little slower.

Basically I think this means a later in the day event because of the delay in the wave and possibly a weakening of the scenario as well. However I still see the vortmax influencing the Victoria / Port Arthur area by 0Z and possibly as far east as Houston by then as well.

I still believe the best moisture and instability will be nearest the coast and the warm frontal boundary should just be a county or so north of there. For severe during the day mid to late afternoon - perhaps Victoria or even slightly north or northwest of there - like Cuero. Houston has a pretty decent forecast sounding for a tornado, but it may be after dark. For consistency I'll still stick with Wharton as the primary by perhaps 21z to 0z. But like I say the area west and north of there toward Victoria / Port Arthur should be primed.

I certainly see potential for supercells in this area, but tornadoes maybe limited simply because of weak surface winds. Along the coast expect LI's from -3 to -6 and pockets of perhaps 1000+ sbcape in a small area briefly. EHI values are not too great and mostly close to 1 or lower, and drop significantly as you move north of the coast. Indeed a lot of the best instability and lower level winds may remain offshore.

Edit: One thing I'll add is this scenario has climatology going for it. It is fairly common this time of year or toward March to get some severe storms along the coast and into the Houston area. Tornadoes are no stranger to the area either. For some reason I don't tend to chase the coast - not sure why. Perhaps it's the flooding potential and inability to maneuver very far south (Gulf). Good seafood though. I'll monitor tomorrow and make my decision about going. I would expect this to be a low visibility situation which is also common in these areas along the coast - another thing I'm not too crazy about.
 
Originally posted by Bill Tabor
After reviewing 0Z run my conclusions and area are similar to before; however note the following changes.

Previous it appeared the low / cold front & warm front would sync well. Now, it appears that the midlevel short wave is a little slower.

Basically I think this means a later in the day event because of the delay in the wave and possibly a weakening of the scenario as well. However I still see the vortmax influencing the Victoria / Port Arthur area by 0Z and possibly as far east as Houston by then as well.

I still believe the best moisture and instability will be nearest the coast and the warm frontal boundary should just be a county or so north of there. For severe during the day mid to late afternoon - perhaps Victoria or even slightly north or northwest of there - like Cuero. Houston has a pretty decent forecast sounding for a tornado, but it may be after dark. For consistency I'll still stick with Wharton as the primary by perhaps 21z to 0z. But like I say the area west and north of there toward Victoria / Port Arthur should be primed.

I certainly see potential for supercells in this area, but tornadoes maybe limited simply because of weak surface winds. Along the coast expect LI's from -3 to -6 and pockets of perhaps 1000+ sbcape in a small area briefly. EHI values are not too great and mostly close to 1 or lower, and drop significantly as you move north of the coast. Indeed a lot of the best instability and lower level winds may remain offshore.

Edit: One thing I'll add is this scenario has climatology going for it. It is fairly common this time of year or toward March to get some severe storms along the coast and into the Houston area. Tornadoes are no stranger to the area either. For some reason I don't tend to chase the coast - not sure why. Perhaps it's the flooding potential and inability to maneuver very far south (Gulf). Good seafood though. I'll monitor tomorrow and make my decision about going. I would expect this to be a low visibility situation which is also common in these areas along the coast - another thing I'm not too crazy about.

Things are coming together better than I anticipated. Under heavy cloud cover this morning and wondering if this may inhibit the initiation of storms this afternoon. That has been the party pooper so far this season down here it seems. My mom services are required from 3:30-6 today and I fear that is when I need to be out by El Campo to enjoy the possibilities today. Much closer and you just can't really chase, Houston goes out to Katy now and it makes it impossible to get anywhere in a short amount of time. DP is already 60, was 46 when I went to bed at midnight. Moisture is there and while I am a total fan of chasing, I really need a good rain event to make up for the foot that we were shorted last year. Problem is that if this goes into a squall line (like is the usual for us), everything will be rainwrapped and then it is game over. I will just stay home and watch, like I normally end up doing.

Totally agree with Bill on the March thing for SE Texas. I have experienced the BEST convection and tornadic storms in March. I anticipate it like y'all drool over May in OK. :lol:

If you end up over here Bill, enjoy your seafood. I am having a seafood fest for SuperBowl. I do know where you can get a killer burger IN Houston if you get stuck there.

Got a new met on my preferred TV station. He is poo pooing the severe event for us and saying it is slated for NE of us. He is all about the umbrella forecast :roll: so is not saying much about the convective outlook for our area.
 
Update: Taking my sweet time at looking at all the models, soundings, parameters, etc. But looks like the game is still on to me. There is a concern with the strong cap, but theta e advection and diurnal weakening and UVV with short wave should overcome later this afternoon / evening. SPC just release an MSD on the situation:
http://www.spc.noaa.gov/products/md/md0093.html

RUC and NAM seem in general agreement with my previous mentioned areas and progression of event. I particularly have my eye on the area near Victoria.

Severe forecast parameters also like the region from Vct to HOU. I'm concerned with late arrival of the wave though.

Mesoscaleanalysis products showing increasing moisture convergence, LI's -4, SCP 6 onshore near CRP and Sig Tor of 1 onshore near CRP. Addtionally EHI 2 near this area and expected to increase as day wears on some.

I note the low circulation center and possible sfc cyclogenesis just sw of the AUS area with trailing trough / cold front extending south into S Tx to just west of VCT and CRP. This feature should continue eastward slowly and eventually be overtaken by mid level wave somewhere between 21z and 0z IMO.

Good luck if you head out. I am considering it.
 
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