textproduct: Austin/San Antonio

KEY MESSAGES

- Increasing potential for localized flooding as widespread rain continues today into tonight, including the eastern Hill County, I-35 corridor, and Coastal Plains.

- Soggy weather likely to continue the eastern two-thirds of the area again on Tuesday.

- Cool weather continues into Tuesday with near normal temperatures Wednesday and a warming trend for late week.

SHORT TERM

(Tonight through Tuesday night) Issued at 125 PM CDT Mon Apr 20 2026

Much of South-Central Texas remains under cool and rainy conditions as a large-scale overrunning pattern persists atop a shallow and anomalously cold airmass for this time of year. A sizable swath of 1 to 3 inches of rain has already fallen mainly along and near I-10 corridor between the Hill Country and San Antonio area, and this has already led to closure of some low- water crossings as soils continue to saturate. VWPs from KEWX and KDFX NEXRADs show southerly flow 1-3 km above the surface, allowing a rich flow of elevated moisture to continue towards a mid-level vortmax over the Permian Basin. These broad rains should continue into Tuesday, with the mass of mostly stratiform rain gradually shifting east with time in tandem with the mid-level disturbance. Distinct from that feature, an upper-level shortwave trough to the west is currently moving across northern Mexico and will serve as a trigger for some deep convective activity beginning in the late afternoon and continuing overnight, starting around the Rio Grande and then along the southern edge of the Balcones Escarpment or US-90 corridor west of San Antonio before continuing east to the I-35 corridor and Coastal Plains overnight, feeding on a strengthening low level jet. This will likely enhance rainfall amounts for these areas, and potentially overlap with areas that have already seen the highest amounts so far today. Given continued moist ascent ahead of the approaching trough, some of the hi-res models indicate potential for training convection within 90th to 95th percentile PWATs. Despite cooler temperatures and meager instability, this repetitive rains may add a swath of additional 2-4" rain atop of what's already fallen. If these swaths train over more built-up areas on the I-35 corridor... a distinct possibility noted in the hi-res models... this would raise concerns for isolated urban and flash flooding, and this is encapsulated in the WPC's level 2 of 4 (Slight) risk for excessive rainfall today into tonight across the eastern Hill Country, I-35 corridor and Coastal Plains. The evolution and track of these storms will need to be closely monitored tonight.

The slower moving, mid-level disturbance currently currently to our west will shift into Oklahoma and continue northeast tomorrow, pushing the favored areas for ascent farther east. The hi-res models tend to show some reduction in rain coverage Tuesday in response, but with moist southerly transport remaining stout, rain chances remain likely tomorrow especially along and east of I-35, along with some isolated to scattered thunder. Temperatures will try to warm up some as southeasterly surface flow makes a rather unconvincing return, but persistent cloud cover will keep highs from climbing much higher than the 60s for most of South-Central Texas.

LONG TERM

(Wednesday through next Monday) Issued at 125 PM CDT Mon Apr 20 2026

A drying trend should start to kick in midweek as the nearby disturbances aloft move farther east, allowing drier mid-level air to return to our area. Daytime temperatures will gradually trend towards seasonably warm levels by Wednesday. Medium chances (50 to 60 percent) for scattered showers continue through Wednesday for the I-35 corridor and Coastal Plains, given the presence of persistent but weaker southerly moist transport.

A prevailing moist southerly wind will stick around throughout the second half of the week, which should eventually bring dew points well above average by the weekend. While upper-level ridging never truly reestablishes over our area later this week, warm air aloft should keep more of a lid on shower activity Thursday and Friday and accentuate a warming trend with highs in the upper 80s to low 90s. A passerby disturbance to our north is accompanied by a slight increase in rain chances Friday, but currently these changes are quite limited (up to about 20 percent) given the likely capping in place. Over the weekend, amplifying troughing over the Four Corners region may lead to another possible round of showers and storms. The zonal orientation of the broader flow is a limiting factor on this potential and blurs the most favorable timing for rain, but ample conditional instability will be in place to provide an environment suitable for thunderstorms. Highs over the weekend are forecast to stay in the 80s to low 90s, with lows returning humid into the 60s and low 70s with the moist south wind.

AVIATION

(06Z TAFS) Issued at 1202 AM CDT Tue Apr 21 2026

An area of showers and thunderstorms is moving away from the TAF sites and any left over light rain will end shortly. In the wake of these showers there are low ceilings. The low level atmosphere is now nearly saturated and fog has either developed or will shortly. The overnight period will have ceilings from MVFR to LIFR and reduced visibility to MVFR/IFR. Once things settle, there won't be much improvement through the day. There is also a chance for more rain to develop after sunrise and continue through the morning. Only DRT shows any hope of rebounding to VFR, and there it will be by early evening.

PRELIMINARY POINT TEMPS/POPS

Austin Camp Mabry 68 63 82 67 / 90 30 50 10 Austin Bergstrom Intl Airport 68 63 82 67 / 90 30 50 10 New Braunfels Muni Airport 70 63 82 66 / 80 30 50 0 Burnet Muni Airport 65 62 79 65 / 80 30 30 0 Del Rio Intl Airport 78 68 83 68 / 10 10 0 0 Georgetown Muni Airport 66 62 80 67 / 90 40 40 10 Hondo Muni Airport 73 65 82 65 / 40 30 20 0 San Marcos Muni Airport 69 63 81 66 / 80 30 50 0 La Grange - Fayette Regional 69 63 81 67 / 80 30 60 10 San Antonio Intl Airport 71 65 82 67 / 70 30 50 0 Stinson Muni Airport 73 67 83 67 / 60 30 50 0

EWX WATCHES/WARNINGS/ADVISORIES

None.