10/31/05 FCST: TX/OK/LA region

[nickgrillo]

A deepening trough at 500mb will move into the southern US during Sunday and Monday... Extending along an axis from the deep south into the great lakes area. The system will begin to induce significant return flow beginning on Sunday, as flow shifts south/southwest in response to the approaching trough. The trough will deepen and progress into eastern TX/AR/LA on Monday. Surface dewpoints should climb into the low-mid 60s... Combined with surface temperatures in the low 70s, ahead of a shortwave and associated mid-level circulation should provide for some decent surface-based instability. Mid-level flow is pretty meager at best across the area (<30knts)... Though decent veering height through a deep layer and moderate low-level flow should contribute to favorable vertical shear profiles supportive of some organized severe thunderstorms across eastern TX/northern LA/AR.

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[nickgrillo]

I'm just quickly glancing at the 84hr NAM for Monday afternoon, and it could be a marginal event... Now, sbCAPE is currently progged to be pretty crappy across most of TX/OK in the warm sector (1000-1500). However, wind fields do look somewhat decent, with 850mb SW at 20kts over a widespread area. A surface low develops in northwest TX at 12z MON, before progressing east into northcentral/northeast TX by mid-afternoon and evening. There does appear to be a cold front that develops across central KS/OK and then curving back into western TX. In the warm sector, surface dewpoints should rise into the low 60s in eastern TX/OK with temperatures into the 70s. Additionally, mostly backed surface flow, beneath 20-30kt SW 850mb flow creates a favorable veering profile - with SRH progged to be in the 150-250m2/s2 range across central/eastern TX/OK. There should be enough forcing along the cold front to get stuff going shortly after 21z -- with a squall line likely setting off and pushing east.

I would have to say, overall, there appears to be a decent threat for a line of thunderstorms -- some severe -- from eastern OK stretching down along the cold front into central TX.

 

[Brett Adair]

Current GFS indicates a positively tilted mid/upper level wave across ERN OK/WRN AR by the 84 hour time period with SFC low placement in the Ark-La-Tex. General analysis overall indicates, some return PBL moisture flow that would be sufficient given frontal forcing for some linear activity in the form of a few severe storms with wind damage being the greatest threat.

84 HR GFS PRECIP/500MB VORT

On the other hand, the ETA indicates the main upper level support will remain well to the north with the greatest height falls remaing over the Great Lakes region as well as southern TX with a small piece of a broken wave diving into the GoM. The 18z ETA solution is a bit slower than the GFS lagging back with a line of storms into Central/East TX during the period.

MESO-NAM 500MB HEIGHT FALLS

This run indicates a limited severe weather threat if any at all with 0-6 KM shear values AOB 40kts. CAPE/LI is also limited as dirurnal decoupling would be ongoing if the front moved in at 06z so SFC energy will be hard to come by.

MSLP/LI MESO-NAM

MESO-ETA 0-3 KM CAPE

Mid level dry advection will push linear organization and continue some threat of isolated damaging wind gusts throughout the period.

MESO-NAM 700MB RH

I will go in between solutions and forecast isolated wind damage right along the frontal boundary in E TX/WRN LA/AR. Limited hail production is possible given cooler temperatures aloft passing to the north of the region. Limited shear and LCL heights will not support tornadic activity.

 

[nickgrillo]

The latest NAM run brings in the trough in a bit more neutrally-tilted and shows a much broader area of surface-based instability (AOA 2500J/KG). Given the low-level moisture/instability to coinside with moderate flow at all levels... And a cold front to set things off... The threat for a damaging squall line across northern/eastern TX is pretty likely -- and given reasonable vertical shear a isolated supercell could also occur. I would expect initiation pretty early in the afternoon... As a the cold front pushes through central/northern TX.

 

[Brett Adair]

Pretty good vertical shear here indicated early on by the RUC40 across TX where LI's are progged in the -4C range by 6 am.



Hourly QPF and Lapse rates show isentrophic ascent present across OK early along a warm frontal axis. As 700-500mb temperatures falls and lapse rates steepen, expect a nice flareup in the form of a convective line later in the period