Parts of usually balmy southern California are under their first blizzard warning since 1989.
The winter storm rolling into the Golden State on Thursday will intensify on Friday.
A massive storm has already brought significant blizzards and temperatures below freezing too much of the northern US.
The cold snap comes as parts of the US southeast basked in a record-breaking heat wave.
By Saturday, forecasters are predicting record snowfall of up to 8ft (2.4m) in the mountains east of Los Angeles.
The mountains are expected to experience powerful winds of 60-75mph (96-120 km/h), while coastal areas may experience flooding.
The icy weather front stretches along the entire US West Coast and the Canadian province of British Columbia.
The winter storm warning is in effect for the coastal Ventura County mountains and Los Angeles County mountains from early Friday until Saturday, the National Weather Service (NWS) said.
Snowfall of up to 5ft is also possible in the mountains around Santa Barbara.
The NWS said the heavy snow will be accompanied by high winds and “near zero visibility.”
California residents are advised to stay home if they don’t have to leave.
There have already been over 200 flight cancellations as of 06:45 ET (11:45 GMT) on Friday morning.
“I have to be totally honest with you guys,” one baffled California meteorologist told viewers this week. “I’ve actually never seen a blizzard warning.”
“Multiple rounds” of snow are forecast to blanket the southern Sierra Nevada mountains in central and western parts of the state.
According to the Sierra Avalanche Center, there will be “dangerous avalanche conditions” across the Sierra Nevada.
On Thursday, schools in the state’s far northwest closed due to the freak weather.
“This is the first snow day we have had in the 31 years I have been with the district,” Jeff Napier, an official with the Del Norte County Schools District, told the Los Angeles Times.
As the storm moves south over the weekend, forecasters say, lower elevation parts of southern California may also experience snow in addition to rain.
The snow elevation may drop as low as 1,500ft – about as high as the famed sign in the Hollywood hills.
Elsewhere in the US, the cold snap has forced schools, businesses, and some state legislatures to close.
Portland, Oregon, had nearly 11in (28cm) of snowfall overnight into Thursday morning, the NWS reported, its second snowiest day ever recorded.
The storm led to the death in Michigan of a volunteer firefighter, who reportedly came into contact with a downed powerline.
Officials in Oregon are also investigating a suspected hypothermia death that they say may be related to the storm.
High winds uprooted a massive redwood tree, which fell into a home in California’s Bay Area, leaving a one-year-old child in critical condition in a hospital.
Across five states, hundreds of thousands of homes and businesses have been without power. Over 700,000 people in Michigan and 80,000 in California still do not have power as of early Friday morning.
More than 8,000 US flights were canceled or delayed on Thursday, according to FlightAware data.
Meanwhile, temperatures in Washington DC hit 81F (27C) on Thursday, a February high not seen since 1874.
More storms are expected to roll through California early next week.