Heavy rainfall and wet melting snow could spark avalanches in the Cascades and cause parts of Western Washington to flood this week, forecasters said.
The National Weather Service Seattle said an atmospheric river this week is “taking its toll” on the Cascades’ snowpack, where some slopes lost as much as 23 inches of snow since Monday morning, according to an X post Wednesday by the agency.
Anna Lindeman, a meteorologist for the weather service, said the atmospheric river parked over" the region, dampening snow in the Cascades.
"It's disturbing the snow that's up there and making it very unstable," she said.
Seattle’s Northwest Avalanche Center issued a warning Tuesday night that the wet snow would create “very dangerous” avalanche conditions on the western slopes of the Cascades until 6:30 p.m. Wednesday. The agency encouraged people to avoid traveling through nearby backcountry areas and said avalanches could run long distances, including into terrain typically considered safe.
The areas at highest risk of an avalanche are between Highway 20 and Interstate 90, including the Mountain Loop Highway and south of Highway 2, according to the agency.
Weather service forecasters also issued a flood watch between Wednesday and Friday afternoons for parts of Western Washington. Heavy rain and melting snow could cause rivers, creeks and streams to overflow in King, Snohomish, Skagit and Whatcom counties, forecasters said.
"We got some pretty decent snow last week, but that's all melting because of the rain," Lindeman said. "That's causing a lot of rivers to rise, and we've already started to see rivers respond."
Sections of the Snoqualmie, Snohomish, Skagit and Tolt rivers are expected to rise above flood level then shrink twice between Wednesday morning and Saturday night, Lindeman said.
The Tolt and Snoqualmie rivers near Carnation, the Snohomish River in Snohomish and the Skagit River near Mount Vernon are all expected to reach moderate flood stage before Saturday, according to Lindeman.
Forecasters warned drivers not to drive through flooded areas or around barricades until after a river falls below flood stage.
Some light snow could fall over the Cascades this weekend, but Lindeman said the rest of the region should see a respite from heavy rain.
"For most of the area, we're going to dry out over the weekend and potentially into Monday," she said. "But it'll still probably be cloudy and typically soupy springtime weather.
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