LOS ANGELES — A historic winter storm slamming California with heavy rains, dangerous winds and rare snowfall intensified Friday as it moved south, shutting down mountain freeways and prompting warnings from forecasters for severe weather not often seen in the state.
The strengthening storm is gaining moisture and becoming a “moderate” atmospheric river, which could compound its effects and dump extreme amounts of precipitation, said Elizabeth Schenk, a meteorologist with the National Weather Service in San Diego.
A string of such storms pummeled California earlier this winter, causing widespread damage, flooding and more than 20 deaths.
The incoming atmospheric river was aimed at the Central California coast Friday morning, but its trajectory was expected to shift toward Southern California, including the Los Angeles area, by Friday afternoon and into Saturday morning, Schenk said.
“A very strong storm system is just beginning to exert its power across southwest California,” a Friday morning update from the National Weather Service in Oxnard warned. The system is expected to bring heavy rains, strong winds and mountain snow to the region through Saturday.
Showers and isolated thunderstorms along the Central Coast have the potential to form waterspouts that could move onshore, creating small tornadoes in western Santa Barbara and San Luis Obispo counties, according to a weather service alert.
As rainfall increased, weather officials also warned of flash flooding and possible rock slides in coastal areas and in the mountains and foothills of southern Santa Barbara County and western Ventura County.
An evacuation warning remained in place for portions of Ventura County until 10 a.m. Saturday because of “anticipated flooding and debris flows.”
Meanwhile, heavy and disruptive snowfall was picking up over Southern California’s mountains, as blizzard warnings took effect for most of the region’s peaks. Many mountain passes had closed early Friday, including Interstate 5 through the Grapevine.
The 5 was closed in both directions through the Tejon Pass after heavy snowfall, the California Highway Patrol and Caltrans said, advising motorists to use U.S. 101. There was no estimate for when it might reopen.
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.
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, forecasters warned.
Snow in the mountains was accumulating “rapidly,” according to Mt. 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 it hopes to reopen this weekend.
At Mountain High Resort in Wrightwood, “things are looking great,” said John McColly, vice president of sales and marketing.
“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.
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.
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.
“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.
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. A flood watch has been issued from Santa Barbara to Los Angeles counties through Saturday. Los Angeles will see the brunt of the storm through the evening Friday, said Eric Boldt, a meteorologist with the National Weather Service office in Oxnard.
The storm system originated in Canada and moved through Oregon, delivering more than 10 inches of snow in Portland and setting the city’s record for 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.
