Sunrise 6:58 AM   Sunset 8:01 PM Moonrise 2:35 PM   Moonset 3:26 AM

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FXUS64 KEWX 181133 AFDEWX

Area Forecast Discussion National Weather Service Austin/San Antonio TX 633 AM CDT Thu Apr 18 2024

New AVIATION

SHORT TERM
(Today through Friday)
Issued at 320 AM CDT Thu Apr 18 2024

Stratus beneath the cap will continue to expand across south-central Texas early this morning and lower. Some areas of fog and patchy drizzle will be possible around daybreak along the escarpment. The stratus should mix out around midday, and with high clouds temporarily clearing off to the east a warmer, hazy, and partly cloudy to mostly clear afternoon is expected.

At the surface, a dryline is forecast to advance east into Val Verde and Edwards counties this afternoon. A cold front is also forecast to drop south through central Texas and the Edwards Plateau this afternoon, and into the Hill Country and southern Edwards Plateau this evening where it overtakes the dryline. With strong diabatic heating, forecast soundings indicate the cap eroding to our north across central Texas and out along the dryline. Isolated convective initiation is forecast after 3 PM north of the forecast area, and perhaps along the dryline and higher terrain of Mexico.

Convective development to the north may increase in coverage through the early evening hours as the front enters the northern Hill Country and near the Austin metro area. Forecast soundings across the northern and western forecast area late afternoon and evening indicate steep, elevated lapse rates producing pockets of MLCAPE values in excess of 3000 J/kg and coinciding with deep layer shear values of 35-40 KT. This will be sufficient to produce a threat for isolated severe storms producing large to possibly very large hail and damaging downburst winds through the Hill Country, southern Edwards Plateau, and Rio Grande early this evening. At question farther southeast, toward San Antonio and east of I-35, will be convective inhibition strengthening into the late evening hours.
There is spread in the HRRR members on how organized and how far south the convection make it before dissipating overnight.

How far south the cold front makes it tonight may be largely influenced by difficult to resolve mesoscale convective processes.
Exact positioning of the cold front near or over the area will also have a big impact on Friday's temperatures as well as convective chances and placement in the afternoon. Confidence in temperatures and rain chance Friday across south-central Texas is currently low.

LONG TERM
(Friday night through Wednesday)
Issued at 320 AM CDT Thu Apr 18 2024

Friday evening will see a chance for some isolated to widely scattered showers and thunderstorms across northern and western portions of the CWA along a slow moving/stalled cold front as a weak perturbation ejects eastward in the 500mb flow. As of now, CAMs are favoring the SDB Mountains in Mexico and the Trans Pecos region of west Texas for initial development mid-afternoon, with potential for these storms to drift eastward through the evening. While not currently outlooked by the SPC, these storms will have potential to be strong to severe with hail and gusty winds.

The front will linger across the area Saturday and Saturday night as a stronger shortwave ejects east across the region. The combination of these two features should result in more widespread shower and thunderstorm development by the late afternoon and evening hours, with northern portions of the area likely seeing the greatest coverage of activity. Widespread cloud cover and rain will limit heating and instability for severe thunderstorms, though a few strong storms still could not be ruled out. The greater concern though will be the potential for heavy rainfall leading to areas of flash flooding as PWATs are forecast to be 150-200% of normal. As a result, WPC continues to have the Hill Country and northern portions of the I-35 corridor and Coastal Plains in a level 2 out of 4 risk for excessive rainfall. Exact rainfall totals are still in question and will largely depend on where training convection sets up, but there is some potential for multiple inches of rain across this level 2/4 risk area.

The front will eventually push south of the area Sunday morning which will bring decreasing precipitation chances and cooler temperatures, with many locations along and north of I-10 forecast to remain in the 60s for Sunday afternoon. Temperatures will then gradually recover through the beginning of next week with dry conditions currently forecast until at least mid-week when forecast confidence and model agreement decreases.

AVIATION
(12Z TAFS)
Issued at 633 AM CDT Thu Apr 18 2024

Stratus prevails across most of south-central Texas and is producing a mix of LIFR to MVFR conditions. Ceilings will gradually rise 14Z-18Z, scattering out and with VFR conditions in the afternoon. We will be watching for convective initiation to the north and west of the region after 21Z, along a weak cold front across central Texas and dryline to the west. Scattered TSRAs to the north are indicated by several CAMs to work south into the Hill Country after 00Z, but less certainty on if they make it into the I-35 corridor (AUS/SAT).
Isolated TSRAs to the west in Mexico may attempt to cross the Rio Grande after 23Z. Due to uncertainty along the I-35 corridor, and lesser coverage along the Rio Grande, we have continued with PROB30 TSRA groups at AUS/SAT/SSF/DRT for now.

PRELIMINARY POINT TEMPS/POPS
Austin Camp Mabry 88 65 81 66 / 10 30 10 20 Austin Bergstrom Intl Airport 87 65 81 66 / 10 20 10 20 New Braunfels Muni Airport 90 67 83 66 / 10 20 10 20 Burnet Muni Airport 86 63 77 64 / 20 40 10 40 Del Rio Intl Airport 97 73 89 71 / 20 20 20 50 Georgetown Muni Airport 86 64 77 66 / 20 30 10 30 Hondo Muni Airport 92 67 84 66 / 20 30 10 30 San Marcos Muni Airport 88 65 82 66 / 10 20 10 20 La Grange - Fayette Regional 88 68 82 69 / 10 10 10 10 San Antonio Intl Airport 90 67 82 68 / 10 30 10 20 Stinson Muni Airport 93 69 84 69 / 10 20 10 20

EWX WATCHES/WARNINGS/ADVISORIES
None.

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