San Antonio sits at the edge of “Flash Flood Alley,” a stretch of south-central Texas notorious for some of the most extreme rainfall rates in the country, where warm Gulf moisture collides with the Balcones Escarpment and can dump enormous amounts of rain in just a few hours. The city averages around 810 mm (about 32 inches) of rain a year, but individual storms have produced record-breaking totals that overwhelm the region’s many normally-dry creeks with little warning. This combination of hilly terrain and thin soil means water runs off fast rather than soaking in. Because flash flooding here can develop faster than a standard forecast can capture, radar tracking is treated as a critical, routinely used safety tool. NWS Doppler radar KEWX (Austin/San Antonio) covers the region.
Learn more: Flash Flood Warning Signs on Radar · Open the full Rain Map