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:
