textproduct: Austin/San Antonio

KEY MESSAGES

- Low chance for a few showers and storms today mainly along the Rio Grande

- Line of strong to severe storms with locally heavy rain possible Tuesday evening/night.

- Active weather pattern from mid-week through the upcoming Memorial Holiday weekend. Heavy rain at times could lead to localized flooding.

SHORT TERM

(Tonight through Tuesday night) Issued at 133 PM CDT Mon May 18 2026

The cap should continue to hold this afternoon, but sufficient warming could spark isolated storms along the Rio Grande in the evening which may push east if they do develop. While only the 12Z HRW ARW and FV3 CAMs depicted deep convection developing in this manner out of the HREF suite, the moist and buoyant environment does increase the background potential relative to typical expectations, so storm chances this evening are but were adjusted higher than the NBM mainly over the Rio Grande Plains and southern Edwards Plateau.

The low-level jet that delivered several days of abnormally breezy and humid conditions will continue for another night (albeit with slightly reduced strength), imparting southerly gusts in the 20-30 mph tonight. The upper-air disturbance over the Central Plains that enabled the LLJ is actively moving farther away, so we expect that winds will start to gradually subside tomorrow.

Humid air will likely persist through the week, but lows Tuesday morning should cap off a streak of mornings with near-record to record-setting mild temperatures. A weak cold front will slowly crawl south towards our local area throughout the day. This front arrives without the support of northerly winds aloft, so this won't be a front known for its northerly post-frontal winds or brisk arrival. Instead, the interaction of the front with the humid airmass stockpiled over our area should produce scattered to widespread shower and storm activity, with that action encroaching upon the Hill Country by the evening hours. Additionally, southwesterly divergent flow aloft should produce isolated to scattered thunderstorms along the dry line atop the higher terrain over Mexico, which may move east towards the Rio Grande and join up with the front. A steady cap should be able to generally mute storm development over South-Central Texas for most of morning and afternoon Tuesday. Despite the clouds and moist air, highs in the 90s with the ample humidity should again boost heat indices above 100F for portions of the Rio Grande Plains and Coastal Plains, with values in the mid to upper 90s elsewhere. However, as the front and dry line get active and move closer, rain chances go up quickly after sunset and temperatures should begin to fall off more than they have on previous days.

The primary period of storminess Tuesday is likely from Tuesday evening into the overnight hours. The SPC has highlighted a Level 2 of 5 (Slight) risk of severe weather with the greatest risk generally along and west of the I-35 corridor. While the simulated radar outputs from the hi-res models disagree in the general arrangement of storms Tuesday evening, the overall environment with weak mid-level flow along the front supports a line of thunderstorms along the front pushing south over the area. There's a somewhat emergent model consensus that this line could reach the Hill Country / Edwards Plateau near or just before sunset and then progress south through the rest of our area before winding down in the pre-dawn hours Wednesday, not too unlike our line of storms last week. The primary severe threat would likely be isolated strong to damaging wind as storms ripple along the front. There could be some isolated large hail potential mainly over the Edwards Plateau, but the rather modest effective bulk shear (generally under 30 kt) and high freezing level will generally limit that risk to only the strongest updrafts. The heavy rain potential will also need to be monitored as well as the front brushes up against the moist, accumulated Gulf air. The WPC has up to a Level 2 of 4 (Slight) risk for isolated heavy rain capable of flash flooding across a substantial portion of our warning area, and the generally weak flow aloft and thick warm cloud depth could support more efficient downpours. Storms that manage to develop ahead of the front would find themselves briefly in a slow-moving environment and add to this rain. This signal is slightly higher in the southern Hill Country Rain totals will generally depend on how quickly the rain-cooled air pushing the line of storms kicks into gear, but the overall prospects for widespread amounts above 1 inch looks likely. A few localized pockets of 3-5" of rain is also hinted at by the CAMs, and this would be commensurate with the moist environment. While the severe risk is more established for northern portions of the CWA, the geographic placement of the heaviest rains is a little more uncertain.

LONG TERM

(Wednesday through next Monday) Issued at 133 PM CDT Mon May 18 2026

Tuesday's front will likely be pushed along by the rain-cooled air from Tuesday night's storms, and Wednesday morning should start out more seasonably with temperatures in the 60s to low 70s. The medium-range model guidance shows several protuberances of vorticity aloft moving over our area Wednesday. However, the atmosphere will probably take some time to recuperate from the preceding night's storms, and even with the moist airmass remaining in place it would not be a surprise to spend most of the day Wednesday rain-free. Still, the continued presence of moisture and a conducive southwesterly flow persisting aloft thanks to broad troughing over the western US means that there will be more opportunities for rain and storms throughout the week. Heavy rain potential will continue with precipitable water values repeatedly near or over the 90th percentile for this time of year. Key elements to watch will be any residual boundaries left over by previous rounds of storms, which can be foci for new storm development, and bundles of vorticity aloft moving over the area to enhance certain windows of opportunity for rain. The precise timing and placement of storms will be based on these factors, which will be sensitive to the evolution of each successive period of storms.

Based on their depictions of mid-level 700mb vorticity, a few of the medium-range models, including the GFS, ECMWF, and their ensemble suite and AI counterparts suggest a favorable period for rain Thursday. The WPC has up to a Level 2 of 4 (Slight) risk for heavy rain during that window. Another conducive period may take shape this weekend. This timing should be considered with broad brushstrokes, as it's still too early to decipher which areas may see heavier rains and when. However, taken altogether, there could be a gradually increasing potential for flash and riverine flooding as each round of rain saturates grounds further. The bottom line is that an active and wet pattern looks likely for the entirety of South Central Texas through the week. Continue to check back as details get clearer over the coming days.

AVIATION

(18Z TAFS) Issued at 1249 PM CDT Mon May 18 2026

Cigs are either MVFR or will trend to MVFR within the hour at area TAF sites. Otherwise, some isolated convection may develop near DRT late this afternoon or early evening. With coverage limited, we will not mention any convection in the forecast at this time. Low clouds and MVFR cigs will return by mid-evening along I-35, with DRT seeing these cigs closer to 09Z. Gusty south to southeast winds will persist through the period. We will need to monitor for a line of convection approaching AUS near or just beyond the end of the current 30 hour forecast period.

PRELIMINARY POINT TEMPS/POPS

Austin Camp Mabry 77 90 71 85 / 10 30 80 60 Austin Bergstrom Intl Airport 79 90 71 85 / 10 30 70 60 New Braunfels Muni Airport 77 90 70 85 / 10 20 70 60 Burnet Muni Airport 75 86 67 82 / 10 40 80 60 Del Rio Intl Airport 76 93 71 88 / 20 20 50 40 Georgetown Muni Airport 77 88 69 83 / 10 40 80 60 Hondo Muni Airport 78 90 70 84 / 10 20 70 60 San Marcos Muni Airport 78 91 71 85 / 10 20 70 60 La Grange - Fayette Regional 78 90 72 85 / 10 20 70 60 San Antonio Intl Airport 78 91 71 85 / 10 20 70 60 Stinson Muni Airport 79 92 71 86 / 10 10 70 60

EWX WATCHES/WARNINGS/ADVISORIES

None.