Another storm will arrive Friday with light to heavy rain throughout the region.
Coast and valley locations are likely to receive 2 to 6 inches of rain, while forecasters are calling for between 5 and 10 inches of rain for the mountains and foothills.
"The storm looks to be the strongest storm to hit southwest California this season", the National Weather Service office for the Los Angeles region wrote. It follows a quick-moving system Thursday that delivered modest rainfall totals, ranging from almost 2 inches in Venado in Sonoma County, 1.33 inches in the Santa Cruz Mountains and less than a half-inch in most cities.
In the mountains, between 1 and 2 feet of snow are possible above 8,000 feet and between 6 and 12 inches above 6,000 feet, the NWS said.
High wind warnings have been issued for higher elevation areas around Los Angeles and all of San Diego County, where officials are bracing for sustained winds of tropical storm force, or 39 miles per hour or greater, along with higher gusts as the storm center nears the coast.
Mandatory evacuations were in place Friday morning for 180 homes in Duarte as officials raised the alert level to red in anticipation of heavy rains. "This will lead to major flash flooding in urban areas".
A Red Cross shelter will be open to evacuated residents at Leisure Village, located at 1200 Leisure Village Drive, beginning at 8 a.m., the Ventura County emergency information website stated.
With soil already soaked from significant rainfall this winter, forecasters warned of the potential for flash floods and debris flows, especially near areas stripped bare by wildfires. The highest surf could be Saturday afternoon with some sets reaching 15 feet.
The rain will continue through Saturday before the skies clear up Sunday.
Flood watches affecting more than 20 million people have been posted for the southern portion of the state, including Los Angeles and San Diego.
Precipitation also moved down the Central Coast counties, but forecasters said it was only a light precursor to a risky atmospheric river taking aim at Southern California.