Atmospheric river storms pound Pacific Northwest

Atmospheric river storms are common along the West Coast. They often look like fire hoses on weather radar.

Last winter, California saw more than a dozen of these storms in a historic season that caused billions of dollars in damage. 

The Center for Western Weather and Water Extremes, which tracks atmospheric river storms closely, forecast this event as a 4 on its scale to 5 based on its intensity and duration. 

Atmospheric river storms are sometimes called “pineapple expresses” in the Northwest because they can draw moisture and warmth from waters near Hawaii, in the Pacific Ocean.

On Tuesday, Seattle broke its daily temperature record at 1 a.m. — at a balmy 59 degrees Fahrenheit. Portland broke its daily record, hitting 64 degrees. A weather service balloon released on the Washington coast Monday measured the most potential precipitation in the atmosphere that had been recorded since 1948. 

In two days, the Cascade Mountains, east of the big cities, received up to 10 inches of rain, Bower said. Lowland regions received between 2 to 6 inches.

When atmospheric river storms strike, they can leave an uneven mark across a region, concentrating rain on a particular river basin. 

In King County, where Seattle is located, emergency managers said they’d been fortunate to deal with only moderate flooding.  

“Most of the impacts here in King County have been fairly mild to moderate — road closures — some sinkholes that have cropped up, minor landslides we’ve been dealing with across roads,” said Brendan McCluskey, the county’s director of emergency management. 

Instead, the storm’s effects centered one county to the north.

“The fire hose got us this time,” said Scott North, the public information officer for the Snohomish County Department of Emergency Management, adding that the Stillaguamish River hit a new record high for flooding. “Homes are wet.” 

Snohomish County floodwaters on Tuesday.
Snohomish County floodwaters on Tuesday. Snohomish County

Drone images shared by the county showed rural homes in a forested landscape inundated with floodwaters. On Wednesday morning, North said parts of the county were continuing to fight flooding. Residents were arranging sandbags as a pulse of water flowed toward downstream communities, he said. 

More rain is expected into the weekend, but forecasters expect it to be relatively minor in comparison.