Areas charred by last month's wildfires in Southern California now face a new threat from a powerful, but fast-moving Pacific storm. Here's what you need to know about this threat.

The weather phenomena are common for California winters, but they could cause dangerous debris flows or mudslides in recently burned areas.

As the downpour intensified Thursday, the National Weather Service issued flash flood and severe thunderstorm warnings for a swath of eastern Los Angeles County. The rain caused a rockslide and pushed mud onto the road in Malibu Canyon, and a large debris flow left about 8 inches (20 centimeters) of mud across a road in the Hollywood Hills.