A flash flood watch was issued Thursday by the National Weather Service out of San Diego for much of Southern California, including Riverside County valleys.
The watch was expected to remain in effect through 10 p.m. Thursday, according to NWS.
"A wave of monsoon moisture is moving across Southern California today and will produce showers and scattered thunderstorms," the weather service stated.
"Easterly flow will allow the showers and thunderstorms to move off the mountains and into the valleys. These slow-moving thunderstorms will produce very heavy rainfall with flash flooding...and debris flows possible in and below recent burn areas."