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FXUS64 KEWX 301140 AFDEWX

Area Forecast Discussion National Weather Service Austin/San Antonio TX 540 AM CST Thu Nov 30 2023

New AVIATION

SHORT TERM
(Today through Friday)
Issued at 140 AM CST Thu Nov 30 2023

KEY MESSAGES

* There is a risk for a few, short-lived tornadoes today 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 today will be between 8am and 2pm.

Isentropic ascent continues to steadily increase ahead of the approaching trough. Ceilings will continue to lower through the predawn hours with areas of drizzle/light rain and fog persisting.
Some embedded showers are also likely through the early morning.

We continue to monitor closely for the potential for a few severe storms capable of producing tornadoes later this morning into the early afternoon in a highly sheared and low to moderate CAPE environment. Low level theta-e advection from the mid Texas coast into the eastern CWA will accelerate through the morning hours. Dew points are forecast to increase into the upper 60s to around 70 mid morning through early afternoon east of I-35 and I-37. HRRR threshold probabilities greater than 80% of surface based CAPE >1000 J/kg are indicated to surge quickly north up the U.S. 77 corridor mid morning into the early afternoon.

Should the instability increase during this time, this will be in a region overlapping an impressive 200-300+ m2/s2 of effective SRH in place in the morning through early afternoon. However, there does still remains some uncertainty on the timing of the instability plume increasing before better shear parameters shift east, and thus spread in the composite reflectivity forecasts from HRRR members is seen. A few members still indicate a few supercellular type structures in our eastern CWA, while others never tap into the instability across our area and keep the deeper convection east of the area. Should parameters come together and updrafts tap into the shear and instability, a few, short-lived tornadoes will be possible, with the window between 8am and 2pm. Significant tornado parameters from more bullish CAMs are indicated to peak around 2-4 across Lee, Fayette, and Lavaca counties midday, with higher values just east of the area into the afternoon, in and near the region where SPC has placed the Level 3 out of 5 risk for severe storms.
There is a relatively sharp gradient of lowering CAPE values on the western side of the instability plume, and therefore we are less confident in the severe risk all the way west into the I-35 corridor near Austin, but will monitor closely.

A pre-frontal trough is forecast to move west to east across the region this 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.

A weak, shallow cold front is forecast to move through the area overnight. Some fog development is possible ahead of the front overnight across the Coastal Plains and possibly near and southwest of San Antonio. The front is forecast to stall near the Texas coast Friday morning. Some weak post-frontal isentropic ascent is indicated by several models on Friday, with the potential for a few showers east of I-35 during the day.

LONG TERM
(Friday night through Wednesday)
Issued at 140 AM CST Thu Nov 30 2023

Seasonable weather can be expected through the long term forecast period. Despite partly to mostly cloudy skies both Saturday and Sunday, the first weekend of December is shaping up to be quite nice, with dry air in place and afternoon highs in the upper 60s to mid 70s and mornings in the 40s and lower 50s. Southwest flow aloft looks to continue and will be the primary culprit with regard to the mid to upper level cloud cover streaming overhead this weekend. Yet another cold front is expected to slide into the CWA late Sunday into early Monday, bringing slightly lower RH values and drier air into the picture.

Beyond Monday, the medium range picture becomes rather muddied.
Ensemble guidance is in the least bit of agreement in the 7-10 range this forecaster has seen in some time. There is the possibility that a low will become cut off from the main flow sometime during the middle to late part of next week, but what happens beyond that is rather uncertain. We'll need to get through the next couple of days and then hopefully we may actually get some better hold on what may play out by the middle to end of next week. In the meantime, find a chance to enjoy this quiet weather in the long term period.

AVIATION
(12Z TAFS)
Issued at 540 AM CST Thu Nov 30 2023

Widespread LIFR ceilings and MVFR to LIFR visibilities prevail early this morning along with -RA and DZ through portions of the Hill Country and along and east of the I-35 corridor. These conditions will hold through the morning hours. Conditions are forecast to slowly improve west to east in the afternoon as a pre-frontal trough moves through the area. Also, there may be a window between 15Z-21Z east of I-35 and I-37 where isolated TSRA develop. This includes a risk for isolated, brief tornadoes primarily near and east of a GYB-3T5 line.

PRELIMINARY POINT TEMPS/POPS
Austin Camp Mabry 73 52 71 48 / 80 0 0 0 Austin Bergstrom Intl Airport 74 53 71 47 / 80 0 10 0 New Braunfels Muni Airport 75 55 74 51 / 80 0 10 0 Burnet Muni Airport 72 48 69 46 / 60 0 0 0 Del Rio Intl Airport 75 52 77 50 / 0 0 0 0 Georgetown Muni Airport 72 50 69 46 / 80 0 0 0 Hondo Muni Airport 70 52 76 48 / 40 0 0 0 San Marcos Muni Airport 73 53 71 48 / 80 0 10 0 La Grange - Fayette Regional 72 58 69 51 / 90 10 20 10 San Antonio Intl Airport 72 55 74 51 / 70 0 0 0 Stinson Muni Airport 73 56 75 52 / 70 0 10 0

EWX WATCHES/WARNINGS/ADVISORIES
None.

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