LOS ANGELES (AP) — Two people died in a submerged car, evacuations were ordered for wildfire-scarred California, and Seattle and Portland faced the rare chance of snowy streets as a wave of storms rolled through the West.

An atmospheric river — a sky-born plume of moisture from the Pacific Ocean — was fueling the weather, which could dump rain and snow over much of the region through Christmas, while the Pacific Northwest was looking at a dayslong cold snap.

On Thursday, two people died when their car was submerged in a flooded underpass in Millbrae, just south of San Francisco. Firefighters rescued two people who had climbed atop a car but they couldn’t reach the fully submerged vehicle, San Mateo County sheriff’s Det. Javier Acosta said.

In the Sierra Nevada, an evacuation warning was issued for about 150 homes downstream of Twain Harte Lake Dam after cracks were found in granite that adjoins the manmade part of the 36-foot-high (11-meter) structure. Authorities began releasing some water, but the dam didn’t seem in any immediate danger, Tuolomne County sheriff’s Sgt. Nicco Sandelin said.

The Sierras could see 5 to 8 feet (1.5 to 2.4 meters) of snow through the holidays, with 10 feet (3 meters) possible at higher elevations, and authorities urged people to avoid traveling through the mountain passes, which could be treacherous.

In Southern California, evacuation orders were issued Thursday night in Orange County because of possible mudslides and debris flows in three canyons where a wildfire last December burned the ground bare. The Orange County Fire Authority reported a mudslide Thursday night in one canyon that affected some roads but no injuries were reported.

The area saw flooding in a storm last week and several homes were red-tagged.

Steve Learned left the area Thursday morning after doing what he could to protect his home.

“The last storm just killed us, buried our road,” he told KABC-TV. “My street turned into a creek bed about 2-and-a-half feet deep with rocks and mud. I hope it doesn’t do it again.”

The Pacific Northwest was facing frigid temperatures and measurable snow was possible in both Seattle and Portland, forecasters said.

Seattle planned to open two severe weather shelters in the evenings starting Saturday. Daytime temperatures could struggle to reach freezing and overnight lows could drop to single digits into next week, National Weather Service meteorologist Reid Wolcott said.

“This is a rare event,” Wolcott said Thursday. “It’s been years since those of us at the weather service in Seattle have seen forecast data like this.”

Portland and Multnomah County planned to open severe weather shelters on Saturday.

“If you don’t have to go out, don’t go out,” Seattle Mayor Jenny Durkan said. She urged people to check on neighbors and pets and help to keep sidewalks clear of snow and ice.

Oregon Gov. Kate Brown issued a state of emergency declaration Thursday evening to remain in effect through Jan. 3, saying expected snow and sustained temperatures below freezing could result in critical transportation failures and disruptions to power and communications infrastructure.

Portland and Multnomah County earlier declared states of emergency.

The storms do have a bright side by increasing mountain snowpacks that provide a substantial amount of water when they melt. Long-term drought conditions continue to blanket nearly 94% of the West, according to the National Weather Service Climate Prediction Center.