A motorist was fatally struck by a tree that was knocked by powerful winds as a winter storm hits California, bringing downpours, wind and snow, authorities said Sunday.

The driver was passing by a residential street in Pacific Beach when a large oak tree fell across a roadway, blocking all four traffic lanes, San Diego Fire and Rescue Capt. Joe Amador said.

The tree, which measured two-and-a-half metres in diameter, also crushed three parked cars that were not occupied, he said.

California Storm

Fierce winds trailing a daylong storm churn the Pacific Ocean off the Los Angeles community of Playa del Rey on Sunday. Strong winds downed dozens of trees and power poles and ripped off rooftops across Southern California. (John Antczak/The Associated Press)

"To the people out here dealing with the rain: be careful, drive slowly and arrive alive," Amador said.

Strong winds downed dozens of trees and power poles and ripped off rooftops — and in one case, solar panels — across Southern California.

Wind gusts topped 80 kilometers per hour in the San Diego area and 105 kph in Malibu, according to the National Weather Service. The highest reading of the day was at Whitaker Peak, north of Castaic, where a gust was recorded at 185 kph.

The storm also dropped up to an inch of rain in some places by 4 p.m. Sunday, and forecasters said up to five centimetres of rain was expected in the valleys of Los Angeles County and as many as seven-and-a-half possible for southwest-facing foothills and mountains.

California Storm

Firefighters examine the huge tree that fell across multiple lanes of traffic in Pacific Beach, Calif., Sunday. (John Gastaldo/The San Diego Union-Tribune via AP)

A flash flood watch was issued for foothill neighborhoods underneath wildfire burn areas, triggering fears of possible mudslides and debris flows. Power outages affecting about 140,000 utility customers were reported across the Los Angeles and San Diego area.

Blinding rain briefly brought traffic to a near-standstill on LA freeways. North of the city, a crash during a heavy downpour involving two trucks closed southbound lanes of Interstate 5 near the Grapevine. There were no immediate reports of injuries.

The storm also churned up high surf along west and northwest-facing beaches. The rough seas prompted authorities to close the piers at Redondo Beach and Manhattan Beach.

To the north, Interstate 80 near Truckee was closed for more than two hours after 29 vehicles got into a pileup amid snowy conditions, KCRA-TV reported.

Another rain storm was expected in the San Francisco Bay Area by Sunday evening. A wind advisory was issued warning of winds gusting up to 80 kph.