textproduct: Austin/San Antonio

KEY MESSAGES

Updated at 1225 AM CDT Tue Sep 29 2026

- Continued above normal temperatures through Wednesday across all of South Central Texas.

- An active pattern will take shape mid to late week, with concerns for heavy rainfall and flooding on the increase, especially Thursday into Friday.

SHORT TERM

(Today through Wednesday) Issued at 1225 AM CDT Tue Sep 29 2026

Some lingering northwest flow aloft was enough to aid in the development of a few showers across the southern Edwards Plateau region yesterday afternoon. Radar estimated a small area of 1/4" to 3/4" in northern Edwards County. Some showers also managed to develop over the coastal plains region with southern Fayette and northern Lavaca showing a few spots of 1/2" to near 1.25".

For today, we will see an increase in southeasterly low-level flow due to lee-side surface troughing over the plains of eastern CO, as well as the remnant low-level circulation from 'Polo' emerging over far west Texas later today. Widespread low clouds will be in place this morning, with some slow clearing of clouds in the afternoon. Temperatures will be above normal, with highs ranging from near 90 to near 100 degrees. Heat index values may briefly approach 108 degrees in the coastal plains, with peak readings closer to 105 degrees along I-35. With the increase in low-level moisture and onset of daytime heating, some isolated to scattered convection will develop from the coastal plains region northward into the I-35 corridor. As we head into the evening and overnight hours, we will continue to see a steady, low-level flow from from the southeast along with mid and upper level moisture increasing from the west in advance of an upper low. This should result in the higher rain chances confined to the western portions of Val Verde County. There is a level 1 of 4 risk for locally heavy rainfall across the far western portion of Val Verde County late Tuesday into early Wednesday.

The weather pattern on Wednesday will begin to change as an approaching upper low over the southwestern U.S. weakens the subtropical ridge axis over Texas and the western Gulf. An increase in southwest flow aloft combined with deep moisture will help generate some isolated to scattered convection during the daytime hours. While we do expect to see another round of high temperatures in the upper 80s to upper 90s, a good amount of cloud cover is anticipated and we could be a little high with our current forecast numbers.

LONG TERM

(Wednesday night through Monday) Issued at 1225 AM CDT Tue Sep 29 2026

We expect to see an increase in the coverage of precipitation Wednesday night beginning out west across the Rio Grande plains as a Pacific front slowly moves in from the west. Plenty of moisture will be in place ahead of this feature as precipitable water values likely climb to around 2" for most areas. WPC continues to show a level 2 of 4 risk for flooding generally along and north of a Del Rio to Austin line, with a level 1 of 4 risk farther east through most of the I-35 corridor.

On Thursday, rain chances will increase significantly across the region as the Pacific front and upper level trough axis approach from the west. The medium range models hint at a southwest to northeast oriented line of convection developing early across the southern Edwards Plateau and northern Hill Country, with convection expected to expand slowly eastward during the day as peak heating is realized. With the Pacific front, well above normal moisture and upper level trough axis, heavy rainfall is likely to develop across a good portion of the region Thursday and into Thursday night. The WPC continues to show a level 2 of 4 risk in place across south central Texas, with a level 3 of 4 over the Hill Country and I-35 corridor.

Rain chances remain high into Friday, but much will depend on the speed of the Pacific cold front. The tail end of the NAM shows the front pushing southward into the coastal plains early Friday morning, which would help shift the focus for heavy rainfall a little farther to the east. The ECMWF and GFS ensembles as well as their AI runs are starting to show some of the heavier precipitation amounts across portions of the Rio Grande plains between Del Rio and San Antonio, northward into the Hill Country. We are still early in this event and as the hi-res members start to pick up on this, additional changes to the forecast are likely. We will certainly need to watch Thursday, Thursday night and even into early Friday morning as models are favoring this time period for the higher rainfall amounts. We could see some widespread rainfall amounts of 2 to 4 inches with local amounts up to 8 inches on Thursday into Friday.

For the upcoming weekend, some remnant upper level energy may hang back to our west as 'Rachel' continues in the eastern Pacific. While our western areas may see slightly lower moisture levels, we will still have plenty of moisture to work with farther east into the I- 35 corridor and coastal plains. Rain chances will remain in the forecast for the weekend into Monday. With good precipitation chances, northerly winds in the lower levels and cloud cover, highs will generally range from the mid 70s to the lower 80s along with overnight lows in the 60s.

AVIATION

(06Z TAFS) Issued at 100 AM CDT Tue Sep 29 2026

Falling heights over the western CONUS and monsoonal instability over the W TX/NM with tropical ties to TC Polo will send the onshore windspeeds upward over the next 24 hours. This is already showing up in the overnight low cloud return over the I-35 Corridor with the Satellite Nighttime Microphysics product picking up on the clouds before 05Z. The latest frames show the pockets of low CIGs in between AUS and SAT, so we'll hold off adding the low CIG period until 07Z. We have DRT getting the CIGs by 11Z as the areas of clouds seen on satellite will have a lot of ground to cover to spread that far west. The winds should get gusty during the daytime, so we'll opt for a summer-like mix out to VFR skies by around 16Z at all TAF sites. There is a mixed bag of solutions for what might develop in the strong onshore flow for this afternoon in terms of convection chances, so we'll hold off any mention of convection for the I-35 sites until we can get a better look at some more rapid refresh solutions. Then, with even higher moisture content in the low levels, we'd expect to see the low CIGs arrive into I-35 by 05Z if not earlier.

PRELIMINARY POINT TEMPS/POPS

Austin Camp Mabry 75 97 75 91 / 20 50 70 100 Austin Bergstrom Intl Airport 74 97 75 91 / 20 50 70 100 New Braunfels Muni Airport 74 96 74 90 / 30 50 70 100 Burnet Muni Airport 73 93 73 85 / 20 40 70 100 Del Rio Intl Airport 77 98 73 89 / 40 20 90 80 Georgetown Muni Airport 74 96 74 89 / 10 50 70 100 Hondo Muni Airport 74 96 74 87 / 20 30 80 100 San Marcos Muni Airport 73 97 74 91 / 30 50 70 100 La Grange - Fayette Regional 75 97 76 94 / 20 40 40 90 San Antonio Intl Airport 76 95 76 88 / 30 40 80 100 Stinson Muni Airport 77 97 77 90 / 30 40 70 100

EWX WATCHES/WARNINGS/ADVISORIES

None.