More than 100 homes were under mandatory evacuation orders in the city of Los Angeles, Jim McDonnell, the Los Angeles police chief, said Thursday morning. The Palisades fire destroyed thousands of homes in the city’s Pacific Palisades neighborhood last month, and hillsides remain vulnerable in the area.

When hills are healthy, vegetation can anchor the soil in place. But when that is burned off, hillsides become vulnerable to erosion, and slopes can come crashing down.

A monster rainstorm was drenching southern California on Thursday, with officials in Los Angeles readying for flooding and landslides in areas burned by last month's huge wildfires.

Southern California was primed for more mudslides and flooding on Friday, especially in areas scorched by last month's devastating wildfires, even as heavy rains that have saturated the Los Angeles area this week tapered off.

A powerful storm is bearing down on California as an atmospheric river drops through the state. While the fast-moving system will affect nearly the entire state on Thursday, of high concern is Southern California as intense rains fall on the heels of devastating wildfires — downpours that could trigger damaging floods and debris flows.