(CBS13/AP) — A storm drenching California has brought much-needed rain in a dry winter but it also washed out a highway, buried the Sierra Nevada in snow and prompted warnings of possible floods and mudslides near areas scorched by wildfires.

The atmospheric river of moisture that barreled ashore in the north early in the week forced a massive Interstate 80 shutdown in Colfax on Thursday.

READ MORE: Dispatch Audio Describes Chilling Details of Boys' Alleged Attack On Own Mother and Brother: 'He Wants To Turn Himself In'

Crashes, spin-outs, and more left traffic backlogged and travelers stranded for hours. I-80 was backed up for miles in some spots.

The storm rolled into Southern California Thursday night, pummeling the region with rain, and was expected to head eastward.

The National Weather Service issued flood advisories for all of Los Angeles County — the nation’s largest with about 10 million residents — and flash flood watches were in place for wildfire-scarred areas in Orange and San Diego counties.

Residents of several Orange County canyons were given an evacuation warning and urged to be prepared to leave quickly if necessary.

“Evacuation routes can quickly become impassable due to mud, debris or flooding,” the Sheriff’s Department warned.

Early Friday, a tractor-trailer flipped on a rainy Los Angeles interstate, and small mudslides blocked garage doors in some neighborhoods.

East of L.A., about 8,200 people were under orders to evacuate foothill neighborhoods beneath the burn scar of last summer’s El Dorado Fire near Yucaipa. Deputies went door to door Thursday urging people to leave in the Oak Glen area.

“We’ve given an evacuation order. You need to heed it,” San Bernardino County Fire Division Chief Grant Malinowski said during a news conference. “Don’t wait, do it now.”

Evacuation orders were also in place for hillside communities in neighboring Riverside County. Meanwhile, the California Office of Emergency Services positioned specialized response strike teams and task forces in 11 counties.

Cindy Gillilan, whose home backs up to the mountain, has lived in Oak Glen in San Bernardino County for 42 years and hadn’t decided whether to evacuate, although she did truck in K-rail barriers to protect her property in case mud and debris flowed down from the denuded hillsides, she told the Riverside Press-Enterprise.

“We’ve had flash floods, but we’ve always had trees on the hills,” she said. “Now there’s nothing but debris and dirt. I think it’s going to be a bad one. I hope not.”

The evacuations came after the storm already had dropped more than a foot of rain along coastal areas and several feet of snow across the central and southern Sierra Nevada. The mountains were expected to see a foot or more into Friday morning, according to the National Weather Service.

READ MORE: El Dorado County Wildlife Rescues Seeing Influx Of Injured Fawns

Blizzard warnings were up into early Friday morning in Mono County at the Nevada border.

“Travel could be near impossible or paralyzed,” the weather service warned. “If you risk travel, you could be stuck in your car for many hours.”

The agency urged people to stay indoors.

“This is a life-threatening situation … even a short walk could be deadly if you become disoriented,” the weather service said.

Yosemite National Park in the Sierras was hit by a snowstorm a week after destructive winds caused major damage, including knocking down 15 giant sequoias and slamming trees onto trucks and buildings. The park, hit with as much as $200 million in damage, would remain closed until at least next Monday after snow knocked branches into cars and buildings, park spokesmen said.

On Thursday, the California Highway Patrol closed a 75-mile (120-kilometer) stretch of Interstate 80 following multiple spinouts along the key route east of Sacramento to the Nevada border west of Reno. No injuries were reported.

Southeast of Yosemite, U.S. Highway 395 remained closed near Mammoth Lakes to the Nevada state line.

Along the central coast, scenic Highway 1 was closed near Big Sur after a section of the roadway collapsed when the cliffside below gave way amid torrential rain. Big Sur Fire said there was no estimate of when the key coastal route would reopen.

“It looks as if about half the road has given way now,” California Department of Transportation spokesman Kevin Drabinksi told the San Francisco Chronicle.

Stormy weather tapered off in Salinas in Monterey County, where mud flows damaged about two dozen homes earlier in the week. The central coastal area, San Francisco Bay Area and other northern regions were expected to remain dry, if cloudy, through the weekend.

Atmospheric rivers are long, narrow bands of water vapor that form over an ocean and flow through the sky. They occur globally but are especially significant on the West Coast of the United States, where they create 30% to 50% of annual precipitation and are linked to water supply and problems such as flooding and mudslides, according to the National Oceanic and Atmospheric Administration.

The atmospheric river is part of a major change in weather for California, which had significant drought conditions for months. The dryness contributed to wildfires that scorched more than 4.2 million acres (17,000 square kilometers) in 2020, the most in recorded modern history.

 

MORE NEWS: 4 People Taken To Hospital After 5-Car Crash On Highway 99 Near Galt

(© Copyright 2021 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)