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FXUS64 KEWX 291135 AFDEWX

Area Forecast Discussion National Weather Service Austin/San Antonio TX 535 AM CST Wed Nov 29 2023

New AVIATION

SHORT TERM
(Today through Thursday)
Issued at 137 AM 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.
* This forecast continues to evolve. Stay weather aware over the next 24 to 36 hours.

An upper level trough off the coast California is forecast to dig into southern California this afternoon, through southern Arizona and New Mexico tonight and into Thursday morning, then into northwest Texas Thursday afternoon. Ahead of this, isentropic ascent will gradually develop today, and then strengthen considerably across South Central Texas Wednesday night into Thursday morning as a 45-50KT low level jet develops. The stratus deck across southern areas early this morning will gradually expand through the remainder of the forecast area late morning, with ceilings gradually lowering southwest to northeast through the afternoon and evening.

A few showers will be possible by later this afternoon southwest of San Antonio. Drizzle and fog is forecast to 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.

The more concerning part of the forecast comes on Thursday with a potential for some severe storms capable of producing tornadoes in a highly sheared and low to moderate CAPE environment. 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. HRRR threshold probabilities greater than 60% of surface based CAPE >1000 J/kg do seem to surge quickly north mid to late morning east of I-35 and I-37, especially near the U.S. 77 corridor. This will be in a region overlapping an impressive 200- 300+ m2/s2 of effective SRH in place in the morning through early afternoon. Composite reflectivity forecasts from a few of the more bullish HRRR members (00Z HRRR and FV3) do show a few supercellular type structures while some other members never tap into the instability across our area. Should the conditional threat occur, the primary window to watch for any short-lived tornadoes will be between 8am and 2pm Thursday.

SPC's Day 2 Outlook has introduced a Level 3 out of 5 risk for severe storms Thursday into portions of Lee and Fayette counties (near the U.S. 77 corridor mentioned). The outlook for a Level 1 to 2 out of 5 risk for severe storms has been expanded slightly west into portions of the I-35 corridor near 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 late afternoon and evening.

LONG TERM
(Thursday night through Tuesday)
Issued at 137 AM CST Wed Nov 29 2023

After an active start to Thursday, we should be wrapping things up by Thursday night as showers and storms exit the region from west to east. After the initial wave of showers and storms in association with a negatively tilted 500mb trough swings through the region, we should see mainly dry conditions through the remainder of the long term period with perhaps the one exception being on Friday evening/early Saturday morning as a few showers attempt to sneak into the Coastal Plains from a weak disturbance sliding up the Gulf Coast.

Despite the passage of a cold front, Friday will probably be the warmest day of the long term period, with highs topping out in the upper 60s for most locations outside of the Rio Grande Plains and Southern Edwards Plateau. Yet another trough will dig over the central CONUS this weekend, but should remain well north of the region, limiting any sort of precipitation potential. As southwest flow aloft doesn't look to end anytime soon, expect continued mid- level moisture to result in, you guessed it, mid to upper level clouds. Temperatures won't be all that bad despite the cloud cover, with afternoons generally in the upper 60s to lower 70s and mornings in the 40s most days. Late Sunday into early Monday, another frontal boundary looks to swing through the CWA, but it is expected to be a dry one. Beyond the weekend, our sights will be set on our next shot at rain, which could arrive as a result of a cutoff low over northern Mexico sometime mid to late next week, but there is still considerable uncertainty in this solution. Stay tuned.

AVIATION
(12Z TAFS)
Issued at 535 AM CST Wed Nov 29 2023

Overcast stratus will prevail today, with ceilings gradually lowering southwest to northeast into MVFR. Ceilings are forecast to more quickly lower this evening, eventually into LIFR overnight, with visibilities in IFR. DZ and -RA are also expected to develop tonight across the Hill Country and along and east of the I-35 corridor, along with embedded SHRAs possible. Thursday morning a few TSRAs will be possible near and east of the I-35 corridor.

PRELIMINARY POINT TEMPS/POPS
Austin Camp Mabry 62 57 73 52 / 0 80 70 10 Austin Bergstrom Intl Airport 63 57 73 51 / 0 80 80 10 New Braunfels Muni Airport 62 58 74 54 / 0 80 70 0 Burnet Muni Airport 60 55 72 47 / 0 50 50 0 Del Rio Intl Airport 59 53 76 51 / 0 10 0 0 Georgetown Muni Airport 62 56 73 49 / 0 70 70 10 Hondo Muni Airport 58 54 72 51 / 20 70 20 0 San Marcos Muni Airport 62 56 73 52 / 0 80 70 10 La Grange - Fayette Regional 65 59 72 56 / 0 80 90 20 San Antonio Intl Airport 59 57 72 54 / 10 80 60 0 Stinson Muni Airport 61 59 74 55 / 10 80 50 0

EWX WATCHES/WARNINGS/ADVISORIES
None.

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