LOS ANGELES — A powerful and potentially dangerous winter storm moved into Southern California on Friday, dumping heaps of rain and snow and prompting severe weather warnings not often seen in the region.
The storm, which has already left a mess in Northern California, was gaining strength and moisture as it traveled south off the Pacific coast. Forecasters on Friday said it was tapping into an atmospheric river system, an enhanced plume of moisture that can deliver large amounts of precipitation.
A string of such storms pummeled California earlier this winter, causing widespread damage, flooding and more than 20 deaths.
By Friday afternoon, the incoming system was making itself felt in Southern California, with rare blizzard warnings in effect in the Los Angeles, Ventura and San Bernardino county mountains. The National Weather Service also issued a flash flood warning for the valleys and foothills of Los Angeles and Ventura counties, warning of heavy rainfall and other potential hazards.
“You could get debris flow issues in burn scars, but also significant roadway flooding that can be much more destructive, and that’s what we’re concerned about,” said David Gombert, a meteorologist with the weather service in Oxnard. “It would be a threat to life and property at that point.”
An evacuation warning remained in place for portions of Ventura County until 10 a.m. Saturday because of “anticipated flooding and debris flows,” officials said. The weather service also warned of waterspouts that could become small onshore tornadoes in western Santa Barbara and San Luis Obispo counties, as well as the potential for rockslides.
Already, heavy and disruptive snowfall was picking up over Southern California’s mountains, spurring the closure of many mountain passes. Interstate 5 through the Grapevine was closed through the Tejon Pass in both directions.
California Department of Transportation spokesman Marc Bischoff said crews were at work plowing the Grapevine, but there was still no estimated time of reopening. Traffic cameras near Lebec and Gorman showed a mixture of rain and snow at various elevations.
State Route 2 in the Angeles National Forest was closed between Newcomb’s Ranch and Wrightwood, and State Route 33 was closed north of Ojai, Bischoff said. The public should not “go up there to look at snow, because they’ll just be turned away,” he said.
Hazards were also forming within city limits, with a steady downpour in Los Angeles on Friday.
In northeast Los Angeles, silty stormwater sloshed down sidewalks and bubbled in gutters. The Los Angeles River roared to life, spewing whitecaps as water churned along the concrete channel.
Street flooding was reported in several areas, including near Hollywood Burbank Airport, where at least five cars were stuck in deep water, and Studio City, where videos showed deep, rushing water around Laurel Canyon Boulevard. Multiple lanes of the 5 Freeway were closed because of “flooding and mud” around Lankershim Boulevard, the California Highway Patrol said. Images on social media showed cars stuck in deep water.
Los Angeles Fire Department spokesman Brian Humphrey said crews were ready to respond to storm-related challenges as needed but, so far, had not received any reports of life-threatening injuries or serious structural damage.
“Right now, it appears to be the city’s holding up pretty well,” he said.
Other areas weren’t faring as well. In the Mojave Desert foothill communities, the National Weather Service said it was receiving reports of drivers stuck in the snow at Lake Elizabeth and Lake Hughes.
The agency warned that blizzard conditions, including several feet of snow, strong wind gusts and “near whiteout conditions,” could make travel impossible through the mountains of Los Angeles, Ventura and San Bernardino counties.
Snow in the mountains was accumulating “rapidly,” according to Mount Baldy Resort, which reported more than a foot of snow early Friday. Its ski resort has been closed since Wednesday because of the wintry conditions, though officials hoped to reopen this weekend.
Martin Rivera of Covina and his family came to the Angeles National Forest to play in the snow on Christmas Eve.
Despite the wintry mess, some were looking forward to the onslaught of fresh powder.
“Things are looking great,” said John McColly, vice president of sales and marketing at Mountain High Resort in Wrightwood.
“We’ve got 16 inches of snow on the ground already, and I believe forecasters are calling for another 2 feet of snow by this time tomorrow,” he said. “So the big stuff is still yet to come.”
A 3- to 4-foot storm would be “about as much as we’ve ever gotten,” McColly said, though he couldn’t be certain of official records.
“That’s definitely in the record-breaking territory,” he said.
As the storm gains moisture, the elevations at which snow will fall are expected to rise, possibly to about 4,000 feet throughout Friday — significantly higher than the rare low-elevation snow and hail seen this week across California, forecasters said.
Total snowfall of up to 12 inches is possible at elevations above 2,500 feet, with 3 to 5 feet of snow falling above 4,500 feet and isolated amounts up to 7 or 8 feet at the higher elevations, according to the weather service.
“It is transitioning to warmer air, and that is lifting the snow levels,” said Eric Boldt, a meteorologist with the National Weather Service office in Oxnard. But a bout of low pressure moving into the area Saturday is expected to drop snow levels back down to 2,500 feet, he said.
Gusty southerly winds are expected through Friday evening, with mountains and foothills reaching up to 75 mph, and coasts and valleys seeing up to 50 mph. The Antelope Valley could see extreme winds, while heavier rain and snow will move across the region.
A light snow falls along Painted Cave Road in the mountains above Santa Barbara on Feb. 23.
The storm will deliver total rainfall amounts of up to 2 to 5 inches along the coast and in valleys, and up to 6 inches in the foothills and mountains below the snow levels.
The storm system originated in Canada and moved through Oregon, delivering more than 10 inches of snow in Portland and setting a city record as the second snowiest day in history. As it moved over the ocean, the storm brought snow to coastal cities in Northern California, including Eureka and Crescent City, and to the Sierra Nevada.
California’s epic snowfall event also comes as a separate formidable winter storm tore through the Midwest, leaving thousands of people without power and leading to a cascade of canceled flights and road closures.
