The aftermath of a “bomb cyclone” after the weather hit Seattle last night, Nov. 20, 2024. (Karen Ducey, The Seattle Times via AP)

ISSAQUAH, Wash. — A major storm has lashed the U.S. Northwest with strong winds and rain, causing widespread power outages, school closures and downed trees that have killed at least two people.

The National Weather Service issued excessive rainfall risks through Friday, and hurricane-force wind warnings were in effect as the strongest atmospheric river — a large surge of moisture — that California and the Pacific Northwest have seen this season overwhelm the region. The storm system, which has hit since Tuesday, is considered a “bomb cyclone,” which occurs when a cyclone rapidly intensifies.

In California, the weather service has extended a flood watch through Saturday for areas north of San Francisco. Up to 16 inches of rain was forecast for Northern California and southwestern Oregon by Friday. Dangerous flash floods, rock slides and debris flows were possible, officials warned.

A winter storm watch was in effect for the northern Sierra Nevada above 3,500 feet, where 15 inches of snow was possible over two days. Wind gusts could exceed 75 mph in mountainous areas, forecasters said.

Heavy, wet snow was expected to continue along the Cascades and parts of far northern California. Forecasters warned of blizzard and whiteout conditions and near-impossible travel at the crossing due to accumulation rates of 2 to 3 inches per hour and wind gusts of up to 65 mph.

Fallen trees hit homes and littered roads in western Washington. In Lynnwood, a woman died Tuesday night when a large tree fell on a homeless encampment, South County Fire said in a statement. In Bellevue, east of Seattle, a tree fell on a house and killed a woman, fire officials said.

Tracy Meloy of Issaquah, Wash., felt well prepared for Tuesday afternoon’s storm, with dinner prepared and lanterns at the ready. But then she spent the night listening to windblown debris hit the outside of her home, including a particularly loud “boom” around 9 p.m. The next morning, she ventured outside to survey the damage to her neighborhood, about 17 miles east of Seattle. .

“Now that I’m standing here in front of the house, I can tell it’s the tree that was across the street,” Meloy said. The tree pulled down power lines in front of her house, and limbs, leaves and other plants were scattered all over the road.

“It looks like a forest instead of a street,” she said.

The number of reports of power outages in Washington fluctuated wildly Tuesday night, but steadily declined to about 460,000 by Wednesday afternoon, according to poweroutage.us. More than a dozen schools were closed in Seattle alone.

About 2,800 customers were reported without power Wednesday in Oregon, 38,000 in California and 10,000 around Carson and Reno, Nevada. Three schools in Reno were closed and semi-trucks were banned from the main highway between the two cities due to high winds. All lifts were closed at the ski resort of Mt. Roses near Lake Tahoe.

The weather service warned people on the West Coast about the danger of trees during strong winds, posting on social media platform X: “Stay safe by avoiding outside rooms and windows and use caution when driving.”

Southbound Interstate 5 was closed for an 11-mile stretch from Ashland, Ore., to the California border Wednesday morning due to extreme winter weather conditions in Northern California, according to the Oregon Department of Transportation. It was expected to be a long-term closure, the department said.

The weather service issued a flood watch for parts of southwestern Oregon through Friday evening, while strong winds and seas shut down a ferry route in northwest Washington between Port Townsend and Coupeville for part of the day.

As Robert and Lisa Haynes of Issaquah surveyed the damage in their neighborhood, they saw downed branches or trees blocking driveways and roads. They were stuck at home.

“It’s like a snow day,” said Robert Haynes, “but without the snow.”

Wind gusts of up to 60 mph were forecast in Juneau, Alaska.

To the east, the first significant snowfall of the season in the Dakotas and Minnesota led to accidents and slippery roads. The weather service said up to 16 inches could fall in North Dakota’s Turtle Mountains and Minot could get up to 8 inches.

Officials advised people not to travel in northern North Dakota, and state troopers in northern Minnesota responded to several crashes, including tractor-trailer crashes on Interstate 94 after the road became slippery from snow and ice.

Winds were expected to be problematic in parts of Montana and Nebraska, with gusts up to 60 mph, the weather service said.

Golden reported from Seattle and Baumann reported from Bellingham, Washington. Jack Dura of Bismarck, North Dakota; Jim Salter of St. Louis; Scott Sonner of Reno, Nevada; Christopher Weber in Los Angeles; and Becky Bohrer in Juneau, Alaska, contributed to this report.