Atmospheric river hits Puget Sound region; avalanche, landslides possible

Update:

The Northwest Avalanche Center in Seattle has issued an Avalanche Warning for the west slopes of the Cascades from the Canadian border to King County, including the mountains in the Mount Baker area, Highway 542, Highway 20 west, and the Mountain Loop Highway. The warning is in effect until 6 p.m. Thursday.

Highway 2 is currently closed east of Stevens Pass near Coles Corner through Tumwater Canyon in the Leavenworth area due to avalanche concerns. The stretch of highway was closed at midnight on Wednesday, and there is no estimated time for reopening.

Rainfall totals in the Cascades from Thursday night through Friday are expected to be in the range of 2 to 5 inches below 5,000 feet, according to KIRO 7 Meteorologist Nick Allard.

As the atmospheric river moves in, the National Weather Service has issued a special weather statement warning residents of Puget Sound about a risk of landslides.

The advisory applies to much of the state, from Bellingham at the north end to Centralia to the south; from the Olympic Mountains on the west end to the Cascades in the east.

Kayla Mazurkiewicz, a meteorologist with the National Weather Service in Seattle, said the soil was already retaining water before this atmospheric river, and now, heavy rain through the weekend could trigger the ground to shift.

“The soil’s already had moisture in it,” she said. “So heavy rainfall means areas could have landslides happen just because the soil is so moist.”

“Olympics, Cascade Mountains, areas near there could definitely have impact, only because there’s going to be more moisture in those areas, but definitely anywhere could be possible because the soil is so saturated,” Mazurkiewicz added.

Between one and three inches of rain are forecast for the lowlands through Saturday, and five to eight inches over the Olympics.
Original:

You know that sound you hear when it is raining hard, and you’re sitting in your home or office? You are going to hear that sound on Thursday.

“It will be a real soaker,” KIRO Newsradio meteorologist Ted Buehner said. “I expect 1-3 inches of rain in the lowlands with the possibility of ten inches of snow in the Cascades.”

Ted said the soil is already saturated and the new rain will increase landslide risks. “Especially on steep slopes like in West Seattle, Magnolia, and the rail line from Edmonds to Mukilteo.”

Here is a timeline and total precipitation forecast for the upcoming storm and atmospheric river event that will impact the region starting Wednesday evening through early Friday. 🌧️#WAwx pic.twitter.com/Y19ODqjV1G

— NWS Seattle (@NWSSeattle) January 11, 2023

The National Weather Service in Seattle reports the rain will begin Wednesday night and go through early Friday.

The cause of all this is “a large area of low pressure … pushing more atmospheric river moisture into California. That low will rotate around a wave that will move the atmospheric river into our area starting tonight,” reports KIRO 7 meteorologist Nick Allard. “Once it starts, we can expect rain to last through a good part of Friday, with Thursday being the heaviest rain day.”

Northern California sees more rain while the south dries out

Nick also said that this soaker will probably bring some urban flooding “where rainwater cannot drain quickly enough.

“The Skokomish River in Mason County will be in flood stage (as it has been for much of the last week), but the Cascades rivers – while running high – will probably only reach minor flood stage or stay below flood stage into the weekend,” Nick continued. “Any eastward shift of the projected band of heavy rain over the Olympic Peninsula would change that river flooding forecast.”

Ted says the forecast will calm down on Friday, but not before dropping heavy snow above 6-7,000 feet in the mountains.

“This will create the possibility for avalanche’s in the North Cascades,” Ted said. “Mountain snowpack will soak up most of the rain in the mountains meaning no flood risk is likely from the mountain tributaries.”

The entire West Coast will continue to be impacted. “California won’t get as much rain as last week, but because it’s all accumulating, things are going to be bad again,” Ted said.

Weather returns to normal over the weekend, but there’s a large weather system off the coast of Japan looming for the future.

Sam Campbell, Meteorologists Ted Buehner, and KIRO 7’s Nick Allard contributed to this story.

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