Winter Storm Sweeps Over Southern California After Battering Oregon

A slow-moving winter storm will intensify over California on Friday, forecasters said, a day after it walloped large swaths of the West with snow and a wintry mix that disrupted travel along a number of major arteries.

Multiple rounds of heavy snow combined with strong winds will create blizzard conditions over high terrain and mountain passes, including in the Sierra Nevada and the Transverse Range in Southern California, the National Weather Service said early Friday.

While the winter weather began in some areas on Thursday, the greatest chances for rain, heavy snow and strong winds in the southern part of the state will be on Friday. Several inches of rain may fall along the coasts and valleys, and the heaviest snow, up to seven feet, may fall in elevations 4,500 feet above sea level. Areas below 2,500 feet are expected to receive up to six inches. Wind gusts of 60 to 75 miles per hour will also play a factor throughout the day.

Early Friday, more than 60,000 customers in California, mostly in the northern part of the state, were without power, according to PowerOutage.us.

Millions of people in the West, mainly in California and Nevada, were under winter weather alerts. The Weather Service issued a winter storm warning for the mountains of Los Angeles, Ventura and Santa Barbara Counties until early Friday, warning of “extremely dangerous mountain conditions.” A rare blizzard warning, for the same areas, will take over from Friday through Saturday.

“This blizzard warning is something that our community is not used to hearing about,” said Jackie Ruiz, the public information officer for the Santa Barbara County Office of Emergency Management. She said the county’s message was simple: “If you don’t have to go out, stay home.”

On Thursday, the storm paralyzed parts of Oregon, trapping motorists for hours while others abandoned their vehicles on the side of the road. Travel disruptions persisted early Friday with the Oregon Department of Transportation announcing closures along at least three highways. On Wednesday, the storm produced 10.8 inches of snow in Portland, giving the city its second snowiest day ever recorded, forecasters there tweeted. Many colleges, universities and school districts will remain closed on Friday.

Snowfall also caused dangerous road conditions in Wyoming, leading to road closures along the southern portion of the state.

The West Coast can be one of the hardest places in the country to predict weather because of the lack of observations over the Pacific Ocean, and the intensity of the storm caught many people — including forecasters — by surprise.

Mark Pestrella, the director of the Department of Public Works in Los Angeles County, said that officials were urging residents in the northern parts of the county to shelter in place beginning on Friday because of expected widespread road closures over the weekend, and to “be ready for basically a snow day” that, while being rare and exciting, could still pose a danger.

“It’s not a weekend for the beach,” he said. “What we’re really recommending is everybody hang tight and let us get the snowfall, and then after that we can get out.”

“Everything is adding up for a major snow event,” said Andrew Rorke, a senior forecaster for the Weather Service office in Los Angeles.

A person standing in downtown Los Angeles can see a 10,600-foot peak that will typically have snow on it, Mr. Rorke said. By Saturday, that snow will extend much farther down the mountain, showing more snow than a typical winter storm.

But don’t expect the Hollywood sign to be lost in a snow-covered hillside.

“The Hollywood Hills are saved from snow, but the San Gabriels behind the Hollywood sign are certainly not,” Mr. Rorke said. (The Weather Service Office in Los Angeles later confirmed that snow or graupel, which looks a bit like hail and has a soft and wet texture, was seen falling Thursday morning near where the signs sits.)

In the Sierra Nevada, the snowpack was already above average for this time of the year, and more snow is in the forecast. Even though snow is nothing new for this region, forecasters in Reno, Nev., were calling it a major storm that will disrupt travel.

“While we cannot definitively say there will be road closures, nor do we have any control over this, past events have certainly brought similar impacts,” the forecasters said.

There is also a high risk for avalanches across the Sierra Nevada on Friday, according to the Avalanche Forecast Center.

This will not be the last winter storm to hit the area; forecasters from all Weather Service offices in California are predicting another storm at the beginning of next week.