Atmospheric river pounds northwest US, killing two and knocking out power across three states

A powerful storm clobbered Washington state on Wednesday, knocking out power to hundreds of thousands of people while disrupting road travel and causing at least two deaths and two injuries.

Winds eased across the region by midday, but the first “atmospheric river” storm of the season has moved to California and is set to bring extreme rainfall by the end of the week, according to forecasters.

A woman was killed on Tuesday when a tree fell on a homeless encampment in Lynnwood, north of Seattle, local officials said. A second woman was killed near Seattle when a tree fell on her home, Bellevue city officials said. Two people were injured when a tree fell on their trailer in Maple Valley, southeast of Seattle.

The storm, with tropical-storm-force winds of 80km per hour and gusts around 110km/h, felled trees and power lines overnight. More than 300,000 homes and businesses in Washington, Oregon and Northern California were without power on Wednesday night, according to Poweroutage.us, down from some 600,000 earlier.

The windstorm and heavy rain also damaged the power system in Canada's Pacific coast province of British Columbia and cut power to some 225,000 customers on Tuesday night, according to provincial electricity provider BC Hydro. By Wednesday evening, about 64,000 customers, mostly on Vancouver Island, remained without power.

An NBC affiliate in Seattle broadcast images of cars smashed by fallen trees and damaged homes.

The Snohomish Regional Fire & Rescue service in western Washington urged residents to stay home, with many trees and power lines down.

“Trees are coming down all over the city & falling onto homes,” the fire department of Bellevue posted on social media. “If you can, go to the lowest floor and stay away from windows. Do not go outside if you can avoid it.”

Schools across western Washington cancelled classes or postponed the start of school on Wednesday.

Heavy snowfall shut down Interstate 5 at the California-Oregon border, the Oregon Department of Transportation said.

“The storm is just beginning,” said Rich Otto, a meteorologist with the National Weather Service's Weather Prediction Center in College Park, Maryland.

The weather service predicted life-threatening flooding across coastal Northwest California on Thursday, with rock slides and debris flows likely.

The storm, called a “bomb cyclone” when it rapidly intensifies, will stall over Northern California in the next few days, Otto said. After the storm peaks on Thursday, rainfall could total 300 to 400mm into Friday, the weather service said. Up to a metre of heavy, wet snow was expected to fall in the mountains per hour, backed by wind gusts up to 100km/h.

A bomb cyclone rapidly intensifies in 24 hours or less when a cold air mass from the polar region collides with warm tropical air in a process that meteorologists call bombogenesis.

Reuters