Powerful storm drenches burn-scarred California

A powerful storm barreled toward Southern California after flooding highways, toppling trees and causing mud flows in areas burned bare by recent fires across the northern part of the US state.

Drenching showers and strong winds accompanied the weekend's arrival of an atmospheric river – a long and wide plume of moisture pulled in from the Pacific Ocean. The National Weather Service's Sacramento office warned of "potentially historic rain."

Flooding was reported across the San Francisco Bay Area, closing streets in Berkeley, inundating Oakland's Bay Bridge toll plaza and overflowing rivers in Napa and Sonoma counties. Power poles were downed and tens of thousands of people in the North Bay were without electricity.

By Sunday morning, Mount Tamalpais just north of San Francisco had recorded 15 centimeters of rainfall in the previous 12 hours, the weather service said.

About 240 kilometers to the north, the California Highway Patrol closed a stretch of State Route 70 in Butte and Plumas counties because of landslides in the massive Dixie Fire burn scar.

"We have already had several collisions this morning for vehicles hydroplaning, numerous trees falling, and several roadways that are experiencing flooding," the highway patrol's office in Oroville tweeted on Sunday. "If you can stay home today, please do. If you are out on the roads, please use extreme caution."

The same storm system also slammed Oregon and Washington state, causing power outages affecting tens of thousands of people. Two people were killed when a tree fell on a vehicle in the greater Seattle area. Eastside Fire & Rescue responded to the scene of the fatalities near Preston, Washington, which is about 32km east of Seattle.

In California's Colusa and Yolo counties, state highways 16 and 20 were shut due to mudslides, the state Department of Transportation said.

Burn areas remain a concern, as land devoid of vegetation can't soak up heavy rainfall as quickly, increasing the likelihood of flash flooding.

"If you are in the vicinity of a recent burn scar and haven't already, prepare now for likely debris flows," the Sacramento weather service tweeted.