A flash flood warning has been issued for east San Bernardino County.
Heavy rains and flash floods have been reported in northwestern Riverside County.
Rain, hail and thunderstorms moved into the Southland Thursday, causing minor flooding in La Cañada Flintridge and an increase in traffic accidents.
At least one Southern California neighborhood was ankle-deep in water and parts of Pasadena were stunned by midsummer showers as a series of thunderstorm cells pass over the region.
A half dozen cars got caught up in a flash flood in Moreno Valley Thursday afternoon.
A powerful winter storm packing heavy rain and thunderstorms is expected to hit Los Angeles Friday, forecasters said.