Evacuation orders and warnings have gone into effect for burn scar areas across Southern California as heavy rainfall threatens dangerous debris flows.

The strongest rainstorm of the year has hit Southern California, prompting mud and debris flows severe thunderstorm and flash flood warnings for recent burn scars. The National Weather Service has issued flash flood warnings for Eaton Fire ravaged Altadena,

In the Los Angeles area, the burn scars that carry the highest risk are those from the Eaton and Palisades fires from January and the Bridge Fire from the fall.

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.

Los Angeles County was placed under an updated flash flood watch by the National Weather Service on Wednesday at 12:03 p.m. The watch is valid for Thursday between 10 a.m. and 10 p.m.

The NWS Los Angeles/Oxnard CA issued a flash flood warning at 3:37 p.m. on Thursday in effect until 8 p.m. for Los Angeles.

An atmospheric river is bearing down on California, bringing with it heavy rains, evacuation orders and flash flood warnings. It's building up to another severe weather setback for an area still reeling from devastating wildfires.