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FXUS64 KEWX 182312 AAA AFDEWX

Area Forecast Discussion...UPDATED National Weather Service Austin/San Antonio TX 612 PM CDT Thu Apr 18 2024

New AVIATION

UPDATE

The NWS Storm Prediction Center has issued a Severe Thunderstorm Watch for portions of South Central Texas including the following counties: Blanco, Burnet, Gillespie, Kendall, Kerr, Llano and Williamson until 1100 PM CDT.

* Primary threats include... Scattered large hail likely with isolated very large hail events to 2 inches in diameter possible and scattered damaging wind gusts to 65 mph possible.

SHORT TERM
(Tonight through Friday night)
Issued at 207 PM CDT Thu Apr 18 2024

Clouds continue to scatter this afternoon ahead of a surface front to the north and a dryline to the west. This dryline will move into western Val Verde County this afternoon with the surface front reaching the northernmost portion of the CWA later tonight where it overtakes the dryline. Late this afternoon and evening, isolated thunderstorms may develop along both of these boundaries. Models indicate potential development over the higher terrain of Mexico late this afternoon and evening which could move into areas along the Rio Grande, although the better potential for storms in South Central Texas will be along the cold front. Storms will likely first initiate north of the area this afternoon in Central Texas. As the front continues south, thunderstorms may move into or initiate over the Hill Country and southern Edwards Plateau this evening.

Steep mid-level lapse rates, upwards of 3000 J/kg of CAPE, and 30-40 knots of bulk shear will lead to a threat for severe storms this evening. Storm coverage should remain isolated to scattered with large to very large hail and damaging wind gusts the main threats.
An isolated tornado also cannot be ruled out over the Hill Country.
Storms may continue to move south into the Rio Grande Plains or portions of the I-35 corridor as the front sags across the CWA around midnight, although the majority of guidance does fizzle out any activity before reaching these areas.

Expect a lull in activity overnight into Friday morning. The exact position of the front will play a big role in temperatures and precipitation chances tomorrow. Latest guidance indicates the front will be draped somewhere over the middle or southern half of the CWA during the afternoon. Went a bit cooler with temperatures tomorrow given the forecast position of this feature. The afternoon should be relatively dry with precipitation chances returning Friday night into Saturday, mainly for the western and northern portion of the area. Isolated to scattered storms may develop near this stalled front with the best chances in the west.

LONG TERM
(Saturday through Thursday)
Issued at 207 PM CDT Thu Apr 18 2024

The long term period will start out active, with a heavy rain event looking increasingly likely Saturday night, followed by several days of temperatures below normal, with Sunday being the coolest day of all.

We start off with the meat and potatoes of the forecast: Saturday's heavy rain threat. The latest WPC Excessive Rainfall Outlook for Saturday night puts areas from the Edwards Plateau, through the Hill Country, the I-35 Corridor from Bexar County northward, along with the Coastal Plains mainly north of I-10 in a level 2 of 4 (slight)
risk for flash flooding. Model guidance remains in fairly good agreement with the NAM12 being a bit of an outlier. For now, we will not put too much stock in the drier solution depicted by the NAM, but it is worth noting that the NAM does well with cold frontal passages. The NAM has the front moving through a bit faster than global models, hence undercutting storms as they develop along and out ahead of the boundary and push east. A shortwave in northern Mexico will team up with the cold front to initiate numerous showers and storms, and with surface dewpoints in the 60s and 70s ahead of the front, we won't have much of any trouble developing widespread showers and storms over the region Saturday evening. Rainfall amounts in excess of 1" are at 60-70% odds per the latest 13Z NBM over the majority of the slight risk area. Once the front shifts south of the CWA, we should see rain and storms come to an end before lunchtime Sunday.

Beyond Sunday, the upper level pattern flattens out considerably, with zonal flow expected through the bulk of the upcoming week.
Temperatures should slowly but surely moderate back into the 80s by Tuesday afternoon. There is an outside shot at some showers or storms Wednesday, but the threat remains quite low at this time.

AVIATION
(00Z TAFS)
Issued at 558 PM CDT Thu Apr 18 2024

All area terminals are forecast to remain VFR through at least 06Z Friday. The exception to this is KAUS as some showers and storms roll over the site between the 03Z-06Z time frame and cigs could lower to MVFR for that period. However, MVFR/IFR cigs are forecast for all of the sites along the I-35 corridor overnight into late Friday morning or as late as 19Z/20Z time frame. Northeast to east winds at 5 to 10 knots are forecast for the I-35 airports through the period while KDRT remains from the southeast and east around 5 to 10 knots with higher gusts mainly on Friday afternoon.

PRELIMINARY POINT TEMPS/POPS
Austin Camp Mabry 63 78 66 78 / 10 10 20 70 Austin Bergstrom Intl Airport 63 79 65 78 / 10 10 20 60 New Braunfels Muni Airport 64 79 66 80 / 10 10 10 60 Burnet Muni Airport 61 74 64 72 / 30 0 30 80 Del Rio Intl Airport 72 87 69 83 / 20 10 50 70 Georgetown Muni Airport 61 76 65 75 / 20 0 30 70 Hondo Muni Airport 66 84 65 81 / 20 10 20 70 San Marcos Muni Airport 63 79 65 79 / 10 10 10 60 La Grange - Fayette Regional 66 80 67 80 / 10 10 10 60 San Antonio Intl Airport 66 80 67 80 / 10 10 20 70 Stinson Muni Airport 68 82 68 82 / 10 10 10 60

EWX WATCHES/WARNINGS/ADVISORIES
None.

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