San Antonio Weather Update: Severe Storm Threat and Record Heatwave—Exact Timing, Safety Tips & What to Expect

Humidity-heavy Gulf air and a slow-moving frontal boundary are turning the normally sunny Alamo City into a storm corridor this week. The National Weather Service’s Austin/San Antonio office kept a Tornado Watch over all of south-central Texas through 10 p.m. Monday, then upgraded portions of Bexar, Comal and Guadalupe counties to a Flash Flood Warning that lasts into early Tuesday morning as repeated thunderstorms track across the I-35 corridor. Why the sudden storm siege • A surface boundary stalled west of U.S. 281 is acting like a conveyor belt, pulling 70 °F dew points northward from the Gulf. • Daytime highs in the low 90s add enough instability for storms to explode each afternoon. • Upper-level winds are weak, so cells “train” over the same neighborhoods, wringing out two to three inches of rain per hour and boosting flash-flood risk. What to expect today, May 27 • Morning: leftover showers with pockets of heavy rain; ponding possible on Loop 410 frontage roads. • Afternoon: another round of strong to severe thunderstorms, especially 3 p.m.–9 p.m. Hail up to 1″ and wind gusts near 60 mph are possible. • Evening: storms sag south toward Pleasanton but fresh cells may redevelop along Hwy 90 and drift across downtown during the Spurs game rush hour. Rain and heat outlook Tuesday: 89 °F/74 °F, 70 % storm chance. Wednesday: 84 °F/73 °F, 60 % storm chance. Thursday: 89 °F/74 °F, locally heavy storms likely, especially west side and Hill Country; NWS signals a “heavy thunderstorm” day. Friday–Sunday: gradual drying trend; highs recover to the low 90s with only isolated pop-ups by the weekend. Impact hot-spots • Low-water crossings: Culebra Rd. at Helotes Creek, Blanco Rd. at Salado Creek and all crossings along Leon Creek are prone to rise quickly. • Commuter bottlenecks: I-10 at Dezavala, I-35 at Walzem, and the upper decks downtown; hydroplaning risk increases once rain rates top 1″/h. • Power grid: frequent cloud-to-ground lightning already knocked out service to 8,000 CPS Energy customers during Monday’s evening line of storms, and scattered outages are likely again. Traveler and event planner checklist • Delay non-essential Hill Country drives; smaller creeks rise faster than city drainage. • Check SAT flight status; inbound traffic was held up to 45 minutes Monday evening and similar ground stops are possible today. • Outdoor graduations and Memorial Day make-up festivities should have a sturdy indoor back-up; most venues along the River Walk have posted contingency plans. Safety quick-hits Turn Around, Don’t Drown remains the mantra—just six inches of moving water can stall a car. Stock vehicles with phone chargers and a small first-aid kit. Have at least two alert sources: a NOAA Weather Radio and a smartphone app with wireless emergency alerts enabled. Looking ahead Long-range guidance hints the blocking high over the Gulf will rebuild by early next week, ushering in classic South Texas heat and finally tamping down the daily thunder. Until then, the pattern favors more late-season soaking—good news for drought-parched Medina Lake but a continuing headache for daily commuters. Keep umbrellas, patience and flash-flood awareness at the ready as San Antonio navigates this storm-studded stretch of springtime weather.