Two people died in a submerged car in California, parts of the Pacific Northwest faced the rare prospect of snow on Christmas Day, and fierce winds were forecast in New Mexico as winter storms swept across the western United States.

In parts of Seattle and Portland, residents were bracing for an unlikely white Christmas, according to the National Weather Service. High winds could knock out power lines in New Mexico. Rain in the Phoenix area could make roads slick and treacherous for drivers.

But it’s a different story for parts of the central and southern U.S., where forecasters say residents will “have to settle for spring-like temperatures” thanks to an unseasonal holiday heatwave.

The extreme weather hitting the West Coast is being driven by an atmospheric river, a sky-born plume of moisture from the Pacific Ocean.

Residents from western Washington to southern California are facing flash-flood warnings, with snow and rainfall expected from Christmas Eve through Christmas night.

On Thursday, flooding in California proved deadly after two people died when their vehicle was submerged in a flooded underpass in Millbrae, south of San Francisco. Firefighters were able to rescue two people who climbed on top of a car, but were not able to reach the fully submerged vehicle, said Det. Javier Acosta of the San Mateo County sheriff’s office.

Meanwhile, evacuation orders were issued on Thursday in Orange County, California, due to possible mudslides and debris flows in three canyons where a wildfire had blazed last December, according to county officials. The orders came as the Orange County Fire Authority reported a mudslide Thursday evening. No injuries were reported in the incident.

In the Sierra Nevada mountains area, around 150 households were given an evacuation warning after cracks were found in granite at the Twain Harte Lake Dam. Sgt. Nicco Sandelin of the Tuolumne County sheriff’s office said there did not appear to be any immediate danger, however.

The evacuation warning came as the Sierras expected to see as much as 5 to 8 feet of snow over the holidays, with the possibility of snow piling up to 10 feet high at higher elevations, according to the National Weather Service. It warned against traveling through the mountains, with the snowfall expected to create hazardous driving conditions.

“Travel will be be hazardous, even impassable at times, in the hardest hit locations with towering snow drifts and whiteout conditions,” the weather service said in a statement.

But while parts of the western U.S. face winter weather woes, residents in parts of the central and southern U.S. are expected to see record-breaking warm temperatures.

“In Christmas-speak, it means Snow Miser has control of the West while Heat Miser has full control of the weather in Southtown with no compromise of snow in Southtown this Christmas,” the National Weather Service said in a festive forecast.

“In contrast to the West, those dreaming of a White Christmas throughout much of the South and East Central U.S. have to settle for spring-like temperatures this Christmas,” it said.

According to the weather service, daytime highs on Christmas Eve from the Middle Mississippi Valley to West Texas are forecast to reach the 70s and 80s, “with some locations not only breaking daily record highs, but potentially challenging December record highs” overall.

Christmas Eve night temperature anomalies are expected to bring potentially “record-breaking warm daily minimum temps” from the Ohio Valley to the Southern Plains. Or in other words, “temperatures so mild, that Santa may want to pack a lighter red coat when going house to house,” the National Weather Service quipped.

By Christmas Day, the “spring-like air mass” delivering warmer temperatures is expected to reach the Mid-South and Mid-Atlantic with highs in the 60s and 70s, bringing more record warmth, “most notably from the Tennessee and Ohio Valleys to ‘Deep in the Heart of Texas’,” the weather service said.

Daniel Arkin and The Associated Press contributed.