LOS ANGELES—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 …