Rain and snow batter Northern California in the latest wave of damaging weather to hit the West Coast

SANTA ROSA, Calif. — A major storm slammed Northern California with rain and snow Wednesday night and threatened to cause flash floods and rockslides in the latest wave of damaging weather to hit the West Coast.

The National Weather Service extended its flood watch through Saturday for areas north of San Francisco as the strongest atmospheric river — a large plume of moisture flowing over land — has seen California and the Pacific Northwest flood the region this season. The storm system had unleashed winds the night before, killing two people and leaving hundreds of thousands without power in Washington state.

Up to 16 inches (about 41 centimeters) of rain is expected in Northern California and southwestern Oregon by Friday. Some areas in Northern California experienced heavy rain Wednesday evening, including Santa Rosa, which saw nearly 5 inches (about 13 centimeters) in 24 hours, according to meteorologist Marc Chenard of the National Weather Service.

Officials warned that dangerous flash floods, rockslides and debris flows were possible. Chenard said about a dozen small mudslides have occurred in Northern California in the past 24 hours, including a landslide that caused a vehicle crash on Highway 281 on Wednesday morning.

The Bay Area National Weather Service warned people that the atmospheric river was focused on the North Bay and “heavy rain is expected to continue tonight Thursday through Friday.” “This will cause landslides and road closures,” he said.

The storm system that first hit Tuesday is considered a “bomb cyclone,” resulting from the rapid intensification of a hurricane.

A winter storm watch was in place for the northern Sierra Nevada above 3,500 feet (1,066 meters), where 15 inches (38 centimeters) of snow was possible for two days. Forecasters said winds could gust up to 75 miles (121 kilometers) per hour in mountainous areas.

The storm had dumped more than a foot of snow across the Cascades Wednesday evening, according to the National Weather Service. Forecasters warned of blizzard and whiteout conditions and that travel would be nearly impossible at the pass level.

According to poweroutage.us, there were nearly 376,000 reports of power outages in Washington Wednesday evening resulting from strong winds and rain the night before. Falling trees crashed into homes and littered roads in western Washington, killing at least two people. A woman died in Lynnwood when a large tree fell on a homeless camp, while another woman died in Bellevue when a tree fell on a house.

More than a dozen schools in the Seattle area closed Wednesday, with some choosing to extend those closures through Thursday.

Nearly 21,000 power outages were reported in California as of Wednesday evening.

Southbound Interstate 5 was closed Wednesday morning for a stretch of 11 miles (18 kilometers) from Ashland, Oregon, to the California border due to extreme winter weather conditions in Northern California, according to the Oregon Department of Transportation. The ministry said a long-term closure is expected.

Hundreds of flights were delayed and dozens canceled at San Francisco International Airport, according to Flight Aware.

The weather service issued a flood warning for parts of southwestern Oregon through Friday evening, while high winds and seas temporarily halted the ferry route between Port Townsend and Coupeville in northwestern Washington.