SAN ANTONIO -- A potent storm system is headed Monday evening to South Texas. This storm system is tapping into Pacific moisture as well as moisture from the Gulf of Mexico. This, combined with a dryline out in West Texas, will create showers and thunderstorms that will move from west to east in the evening hours of Monday though the early morning hours of Tuesday. Some of these storms will be strong to severe with large hail, high winds, heavy rainfall, and isolated tornadoes.

The Storm Prediction Center in Norman, Okla., has issued a slight risk for South Central Texas and a moderate risk from Rocksprings to Uvalde, and up to San Antonio and points northward. A moderate risk means that there is an increased risk for tornadic activity and severe storms.

For San Antonio, the best chance for severe weather will be after midnight through the morning commute Tuesday morning.

A Flash Flood Watch is in effect for Blanco, Cladwell, Gillespie and Hays counties until 1 p.m. Tuesday

Keep it tuned to KSAT-12 and KSAT.com for any severe weather alerts. Steve Browne will be tracking the weather tonight and Steve Roldan will be watching the radar Tuesday morning.