LOS ANGELES - A powerful storm continues to slam the US West Coast on Tuesday with heavy rain, snow and wind, as flood watch remains in effect across California.

Southern California is once again "under the gun" for numerous instances of flash flooding as the main band of atmospheric river rainfall focuses through the overnight hours there, said the US National Weather Service (NWS) Weather Prediction Center.

A Pacific storm with atmospheric river will continue periods of heavy rain, mountain snow, and strong winds across much of California through Tuesday, according to NWS.

Heavy rain is falling across the state, flooding roads and threatening to trigger landslides. Nearly the entire population of California remains under flood alerts.

There have been numerous reports of flooding and rock and debris across roads in Los Angeles. Several roads across the state have been closed because of flooding and rockslides, California's transportation agency reported.

NWS warned of locally considerable flash, urban, and small stream flooding impacts along the Transverse Ranges in Southern California.

Several feet of heavy snow is likely above 6,000 feet in the Sierra and far northern California mountains, with additional heavy snow above 7,500 feet for southern California, according to NWS.

The NWS Weather Prediction Center has issued a Moderate Risk of Excessive Rainfall along coastal Southern California through Tuesday night.

Officials are urging people to stay off roads to avoid the risk of flooding and landslides.

Precipitation has picked up dramatically recently in California, as winter storms have driven heavy rain and snow across the state. The latest tempest has brought devastating impacts, including destructive mudslides and floods.