LOS ANGELES — Debris flows brought on by the strongest atmospheric river of the season swept a car off a southern California highway and into the ocean and left roads submerged in sludge.

While the heavy rains from the storm hitting the region began to ease Thursday night, the risk of rock and mudslides on wildfire-scarred hillsides continued Friday since dangerous slides can strike even after rain stops, particularly in scorched areas where vegetation that helps keep soil anchored has burned away.

One member of the Los Angeles Fire Department was in the vehicle when it went into the water in Malibu and was able to exit with minor injuries, department spokesperson Erik Scott said on the social platform X.

In Pacific Palisades on Thursday, one intersection of the highway was submerged in at least 3 feet (about 1 meter) of sludge, with some drivers trying to force their way through and police officers pushing one vehicle through the muck. Bulldozers worked to clear the roads not far from where just weeks ago they moved abandoned cars after people fleeing last month’s wildfires got stuck in traffic and fled on foot.

In north Altadena, a road near the Eaton Fire burn scar was also covered in several feet of mud, vegetation and trees as a flood of water overcame concrete blocks put in place to prevent such debris flows. The area was mostly deserted.

In neighboring Sierra Madre, the city issued evacuation orders for areas affected by the Eaton Fire, warning in a social media post that fire, police and public works personnel would not enter areas experiencing active mud and debris flows and anyone who remained in a home under evacuation orders would need to shelter in place until areas are deemed safe for city personnel to enter.

Azusa police said the roof of a grocery store partially collapsed while shoppers were inside the store Thursday evening, but everyone got out safely, KABC-TV reported.

The weather service was expected to survey damage Friday at a mobile home park in Oxnard that was hit by 60-mph (96-kph) wind gusts on Thursday afternoon, the Los Angeles Times reported. They would determine whether there was a weak tornado at the park, meteorologist Carol Smith said.

To the north, snow and ice contributed to major pileups on highways in Oregon and Washington, injuring at least 10 people, as a winter storm descended on the Pacific Northwest.

The West Coast storms are just the latest in a week of bad weather across the U.S. that cut power to tens of thousands.

Meanwhile, meteorologists warn that the United States is about to get its 10th and coldest polar vortex stretching event this season. Weather forces in the Arctic are combining to push the chilly air that usually stays near the North Pole into the United States and Europe. The latest projected cold outbreak should first hit the northern Rockies and northern Plains on Saturday and then stick around all next week.

Too Much Rain Too Quickly in California?

As the downpour intensified Thursday, the National Weather Service issued flash flood and severe thunderstorm warnings for a swath of eastern Los Angeles County. The rain caused a rockslide and pushed mud onto the road in Malibu Canyon, and a large debris flow left about 8 inches (20 centimeters) of mud across a road in the Hollywood Hills.

Southern California reported 1 to 2 inches (2.5 to 5 centimeters) of rain in coastal areas and valleys and 3 to 6 inches (7.6 to 15.2 centimeters) across the coastal slopes on Thursday, according to the weather service.

More than 30,000 people in California were without electricity, according to PowerOutage.us.

Evacuation orders and warnings were issued in areas where hillsides were scarred by the Palisades Fire, the most destructive in LA history. In addition to burning the vegetation that keeps soil in place, the fires also added loose debris to the landscape, including ash, soil and rocks.

Ahead of the storm, officials distributed sandbags, positioned rescue swimmers and told residents to have go-bags ready. Sandbags and temporary concrete barriers were in place across Altadena, where the Eaton Fire destroyed thousands of homes.

Despite recent storms, much of Southern California remains in extreme or severe drought, according to the U.S. Drought Monitor. Daniel Swain, a climate scientist at the University of California, Los Angeles, said that while the area is desperate for rain, this storm might bring too much too quickly.

In Altadena, Mehran Daoudian prepared by laying tarp over a hole in his home’s roof where fire burned through it last month. Daoudian said he was grateful that city workers arranged sandbags and concrete barriers in his neighborhood over the past few weeks.

“I did not leave the cars on the street because with the mudslide, (they) might go down,” he said.

Near the burn scar for the Airport Fire in Orange County, Trabuco Canyon Road was overtaken by mud and debris, Orange County Public Works posted on social media.

In the San Francisco Bay Area, there were blackouts, small landslides and inundated roadways. Authorities urged people to evacuate Felton Grove, a small community along the central coast, as the San Lorenzo River threatened to top its banks.

In neighboring Nevada, the weather service said it recorded a measurable amount of rain in Las Vegas, ending a streak of 214 days without precipitation.

And in northern Utah, rain and snow created dangerous conditions on mountain roads leading to ski resorts. The state Department of Transportation issued a road safety alert warning of a mix of heavy snow and rain through Friday.

Pacific Northwest Ice Storm

First responders searched every vehicle in a pileup Thursday near Multnomah Falls, about 25 miles (40 kilometers) east of Portland, Oregon, the Multnomah County Sheriff’s Office said. The office initially said more than 100 cars were involved, but the state transportation department later said the number was 20 to 30 vehicles. Oregon State Police said four people were taken to hospitals with minor injuries.

The pileup happened during near-whiteout conditions in the westbound lanes of Interstate 84, authorities said. An SUV caught fire, but its occupants escaped.

Multnomah County officials extended a state of emergency through at least Friday and said eight shelters would be open. Officials said 489 people went to the shelters Wednesday night.

Wind chills could dip to 10 degrees (minus 12 Celsius) in Portland, the weather service said.

In southern Washington, six people were taken to hospitals with injuries in another pileup of 22 vehicles on Interstate 5 near the Cowlitz River, state patrol spokesperson Will Finn said. There were 95 crashes Thursday in five counties in the state’s southwest.