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FXUS64 KEWX 300445 AFDEWX

Area Forecast Discussion National Weather Service Austin/San Antonio TX 1045 PM CST Wed Nov 29 2023

New AVIATION

SHORT TERM
(Tonight through Thursday night)
Issued at 155 PM CST Wed Nov 29 2023

KEY MESSAGES

* On Thursday there is a risk for a few, short-lived tornadoes near and east of the I-35 and I-37 corridors. The greatest risk is forecast to be along and east of the U.S. 77 corridor.
* The primary time window for any severe storms Thursday will be between 8am and 2pm.

An upper level trough along the California coast is forecast to dig through southern Arizona and New Mexico tonight and into Thursday morning, then into northwest Texas Thursday afternoon. Ahead of this, isentropic ascent will strengthen considerably across South Central Texas tonight into Thursday morning as a 45-50KT low level jet develops.

Drizzle and fog will develop tonight, along with an expansion in coverage of showers into the Hill Country, I-35 corridor, and Coastal Plains. Height falls ahead of the shortwave trough will result in steepening H7-H5 lapse rates through the night and into Thursday morning, and there is a low chance of isolated, elevated thunderstorms to develop overnight into the early morning hours.

There will be a potential for some severe storms capable of producing tornadoes during the day Thursday. Very strong vertical wind shear will develop along with low to moderate CAPE. The risk is conditional on where and to what degree the instability plume sets up across eastern areas of the CWA and the ability for any storms to actually tap into it. The most likely overlap of high shear and CAPE will be near the U.S. 77 corridor. Model soundings show an impressive 200-300+ m2/s2 of effective SRH in place in the morning through early afternoon. If storms form in this environment they will likely develop into supercells capable of producing tornadoes.
The primary time frame for any short-lived tornadoes will be between 8am and 2pm Thursday. SPC's Day 2 Outlook has a Slight (Level 2 out of 5) risk for severe storms Thursday into portions of Lee, Lavaca, and Fayette counties (near the U.S. 77 corridor mentioned) and a Marginal (Level 1 out of 5) risk for severe storms to the west into portions of the I-35 corridor including the Austin metro area.

A pre-frontal trough is forecast to move west to east across the region Thursday afternoon, with precipitation chances gradually shifting away from the I-35 corridor early afternoon and eventually east of the U.S. 77 corridor by late afternoon and evening.

A cold front will move through the CWA Thursday night bringing in cooler, drier air. Winds will become northerly to northwesterly. By Friday morning the new airmass will reach I-35 and there will be a good range of low temperatures with near 60 over the Coastal Plains and middle 40s over the Hill Country.

LONG TERM
(Friday through Wednesday)
Issued at 155 PM CST Wed Nov 29 2023

The short version: Despite a cold front passing through just before the start of the long term, near to slightly above normal daytime high temperatures are forecast Friday through early next week. No rainfall is expected, with the exception of a very low chance for a shower on Friday evening across mainly Lavaca County.

A few more details: Friday morning, an H5 trough over the SW US and NW Mexico will allow for SW flow aloft over TX. This will remain the case through much of the weekend, though troughing will eventually shift over our region on Sunday and quickly exit to the east Sunday night. Morning cloud cover will be expected over much of the region, and the Coastal Plains may remain mostly cloudy during the daytime Friday through Sunday. Slightly drier air will be ushered in as the trough exits, which should allow for cooler overnight lows potentially into the upper 30s by Tuesday and Wednesday mornings. A rather notable ridge will develop over the western CONUS by Tuesday and Wednesday, and so we expect no precipitation at least through this time next week.

AVIATION
(06Z TAFS)
Issued at 1022 PM CST Wed Nov 29 2023

Light winds and persistent drizzle overnight will probably lead to some LIFR and potentially VLIFR conditions toward daybreak. Will show a trend of the lower VSBYs impacting DRT mostly before daybreak and progressing east to I-35 sites around daybreak. As more sites crater, we may end up with prevailing 1/2SM or less VSBYs over a good part of the area. Precip areas will keep certainties low on timing. Once the subsidence side of the shortwave arrives toward midday, CIGs should pick up to perhaps above 1000 ft as winds become SWly at over 10 knots. VFR skies are expected by early Thursday evening for most areas and by mid afternoon for DRT.

PRELIMINARY POINT TEMPS/POPS
Austin Camp Mabry 56 74 51 69 / 60 60 0 0 Austin Bergstrom Intl Airport 57 74 51 69 / 60 60 0 0 New Braunfels Muni Airport 58 73 53 72 / 60 50 0 0 Burnet Muni Airport 55 73 48 67 / 40 40 0 0 Del Rio Intl Airport 53 74 50 75 / 10 0 0 0 Georgetown Muni Airport 56 73 49 67 / 60 60 0 0 Hondo Muni Airport 55 71 51 74 / 60 30 0 0 San Marcos Muni Airport 57 72 52 70 / 60 50 0 0 La Grange - Fayette Regional 59 73 56 67 / 70 80 20 0 San Antonio Intl Airport 57 71 53 72 / 60 40 0 0 Stinson Muni Airport 59 72 54 74 / 60 40 0 0

EWX WATCHES/WARNINGS/ADVISORIES
None.

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