LOS ANGELES (CBSLA.com) — More thunderstorms and heavy rain could hit Southern California again Friday, just a day after rain sent mud and debris into homes and severed roads, including Interstate 5, the main artery between Los Angeles and California’s Central Valley.

Forecasters say Friday’s thunderstorm is expected to move over the region slowly, exacerbating the impact of heavy rainfall, so people living below slopes denuded by wildfire should take precautions, a National Weather Service statement said.

READ MORE: Bob Dole, Who Overcame Severe WWII Wounds To Lead Senate GOP And Run For President, Dies At 98

Thunderstorms were starting to develop near Wrightwood and Pearblossom in the eastern San Gabriel Mountains and Antelope Valleys as early as 11 a.m, forecasters said.

A flash flood watch will be in force Friday afternoon through the evening in the Antelope Valley and mountain areas in Los Angeles, Ventura and Santa Barbara counties. A moist and unstable atmosphere will prevail in those areas, “bringing the threat of strong and locally severe thunderstorms,” according to the NWS.

Numerous road closures are in effect in the Antelope Valley and the mountains of Los Angeles County due to Thursday’s episodes of flash flooding and mud and debris flows. Some motorists looking for an alternate route, however, likely were caught in a separate debris flow in Kern County, where up to 20 feet of mud slid onto state Route 58 in Tehachapi, trapping as many as 200 vehicles.

READ MORE: Inside SoCal: 12/5 Wrap-Up

“The threat of additional heavy rainfall … could impact clean-up operations and force additional road closures,” forecasters warned. “There will be the potential for additional flash flooding as well as mud and debris flows across the watch area Friday afternoon into early evening.”

The NWS said there was also a chance of lightning, gusty winds and hail.

Saturday’s forecast does not include any chance of rain.

MORE NEWS: 1 Dead, 4 Injured In Multi-Car Crash In Anaheim

(©2015 CBS Local Media, a division of CBS Radio Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. Wire services contributed to this report.)