First Alert Weather Alert Day for isolated showers and thunderstorms for valley and mountains Published First Alert Weather Alert Day for isolated showers and thunderstorms for valley and mountains First Alert Weather Team has issued a First Alert Weather Alert Day starting today Sunday, July 25th through Monday morning. There are chances for showers and isolated thunderstorms beginning Sunday afternoon and lasting through the evening. More showers and thunderstorms could continue through Monday. The National Weather Service in Phoenix issued a Flash Flood Warning for Riverside County until 10:15 p.m. Mountains in a Flash Flood Watch until 11 p.m. tonight.