textproduct: Austin/San Antonio

KEY MESSAGES

Updated at 621 PM CDT Thu Sep 17 2026

- Isolated showers and storms are possible across the coastal plains and I-35 corridor today. Heavy rainfall and cloud to ground lightning is possible with any storm that develops.

- Above average temperatures continue through the weekend.

SHORT TERM

(Tonight through Friday night) Issued at 1259 PM CDT Thu Sep 17 2026

17z Mesoanalysis this afternoon indicates southeasterly 300mb & 500mb flow across the region as the axis of stout mid to upper level ridging gradually slides westward across the lower Mississippi River Valley. At the surface, light easterly to southeasterly flow prevails across our region as an area of expansive ridge remains elongated to our northeast across most of the eastern United States. A subtle wind shift across coastal southeastern Texas in the 850mb and 925mb layers reveals the northern extent of a weak surface trough that is being steered into our area via anticyclonic flow around aforementioned deep-layer ridging. Increased moisture and instability (SBCAPE values increasing to 3000-4000 J/kg) associated with this feature will result in a threat of isolated showers and storms for the remainder of this afternoon into the early evening hours as a instability and low level lapse rate gradient gradually shifts westward in tandem with the weak low level perturbation. Out ahead of the gradient, atmospheric moisture remains largely confined to the lowest 1-2km of the boundary layer with a substantial amount of dry air throughout much of the vertical column. The latest ACARS profile from KSAT depicts some of this drier air mixing down to the surface which has kept cumulus activity low topped and shallow in nature. Maximized ascent along the gradient boundary and moisture surge will serve as the main mechanism for convective initiation and propagation. Even so, residual dry air in the column may act to inhibit the spatial coverage of showers and storms, hence the forecasted slight chances. HREF LPMM (Localized Probability Matched Mean) guidance pinpoints widespread accumulations below 0.25" with the potential of one or two isolated pockets of 1" or greater. Outside of any showers/storms and resultant cloud cover, temperatures will remain in the upper 90s this afternoon with heat indices in the 100 to 108 degree range.

As surface high pressure establishes further across the region on Friday, the weak surface trough will push westward across the region, continue to weaken, and primarily reside across the Rio Grande area. This will focus the highest perceptible water values and greatest instability across the western half of our area, resulting in isolated shower and thunderstorm activity. Deterministic and ensemble guidance continue to depict the arrival of a plume of drier air in much of the vertical column during the day on Friday which could mix down to the surface with diurnal heating. This will act to keep apparent temperatures closer to 100- 105F and below heat advisory criteria even with ambient temperatures forecast to once again reach the middle to upper 90s once again during the afternoon hours.

LONG TERM

(Saturday through next Thursday) Issued at 1259 PM CDT Thu Sep 17 2026

A consensus of ensemble and deterministic model continue to depict the axis of expansive mid to upper level ridging sliding directly over Texas during the upcoming weekend as 500mb heights and temperatures increase. 12z LREF guidance indicates the strength of the high pressure aloft will indeed be anomalous as 500mb heights are forecast to near the 99th-100th percentile for this time of year based on climatology. With warm temperatures aloft (-4C to -5C) and a lack of synoptic forcing, our weather will primarily be driven by mesoscale circulations on Saturday as a few isolated showers and storms cannot be ruled out closer to where the greatest instability and low level moisture resides; the middle Texas coast. By Sunday, model guidance hints at the arrival of a short wave across northern Texas out ahead of the next lobe of a mid-level trough propagating eastward via the southern jet- stream. This will act to erode the mid to upper level ridge in place and veer mid to upper level flow to a southwesterly direction resulting in a slight moistening of the mid- level of the atmosphere. At the surface, a frontal boundary is forecast to slide southward into northern Texas and become stationary during the first part of next week. Increasing moisture pooling to the south of the boundary and an active southern branch of the jet- stream just to the north of our area could result in diurnally driven isolated to scattered showers and thunderstorms each day through mid-week. High temperatures are forecast to remain relatively consistent through Wednesday, residing in the middle to upper 90s across most of the area with the exception of the low 90s across the Edwards Plateau. Peak apparent temperatures are forecast to reach the 100-105 range each afternoon.

AVIATION

(00Z TAFS) Issued at 621 PM CDT Thu Sep 17 2026

An 8-15 kt east to southeast prevailing wind will continue into the evening across the area before weakening tonight. Residual outflows from dissipated convection may produce temporarily gustier conditions through the evening. Cirrus should prevent CIGs from developing and maintain VFR through the next 24 hours for most of the area, but lower MVFR CIGs are forecast to develop near and around KDRT closer to 12Z before lifting with more confident trends noted in recent models since the 18Z TAFs. Spotty SHRA may again develop over South Central Texas after 18Z, but chances are low.

PRELIMINARY POINT TEMPS/POPS

Austin Camp Mabry 76 99 73 99 / 10 0 0 0 Austin Bergstrom Intl Airport 75 99 72 99 / 10 0 0 0 New Braunfels Muni Airport 74 98 71 97 / 10 10 0 0 Burnet Muni Airport 73 96 70 96 / 10 0 0 0 Del Rio Intl Airport 77 97 76 98 / 20 10 0 0 Georgetown Muni Airport 75 98 72 98 / 10 0 0 0 Hondo Muni Airport 74 97 72 97 / 20 10 0 0 San Marcos Muni Airport 73 99 71 98 / 10 0 0 0 La Grange - Fayette Regional 74 98 71 98 / 10 0 0 0 San Antonio Intl Airport 77 97 74 97 / 20 10 0 0 Stinson Muni Airport 76 99 73 99 / 20 10 0 0

EWX WATCHES/WARNINGS/ADVISORIES

None.