Updated Dec 6, 2023 - Science

Powerful atmospheric river floods Pacific Northwest with heavy rains

A woman stands near her partially submerged car on a road that was closed due to flooding in Snohomish County, Washington.

A driver stands near her partially submerged car on a road that was closed due to flooding in Snohomish County, Washington. Photo: Snohomish County Sheriff's Office/X

A potent atmospheric river storm system that's flooding the Pacific Northwest with heavy rains this week was disrupting travel and left over 17 million people under flood alerts Tuesday night.

The big picture: At least two people have died in the parade of storms that have prompted water rescues, road and school closures, and forced Amtrak to cancel the train service between Seattle and Portland through Thursday because of a landslide.

  • Officials in Portland, Oregon, told the Oregonian crews had recovered two bodies from two different flooded creeks on Monday and Tuesday.

State of play: The National Weather Service said several inches of rainfall were forecast over the next couple of days for Washington, Oregon and northern Idaho from this "robust" type of atmospheric river — known as a "Pineapple Express because moisture builds up in the tropical Pacific around Hawai'i.

  • "Warm air associated with the stream of moisture extending from the subtropical Pacific will continue to allow for very high snow levels through early Wednesday, which will exacerbate the flooding potential due to snowmelt and increased runoff," per an NWS Tuesday night forecast discussion.
  • "Numerous flood watches, warnings and advisories are in effect along the Washington, Oregon, northern California coastline, central and eastern Washington and Oregon, and portions of northern Idaho and far northwest Montana," the NWS said.
A screenshot of a Twitter photo post showing a collapsed road with the comment: "UPDATE: SR503 near Cougar (MP 35.7) remains CLOSED until further notice, due to water over the roadway & damage underneath. Crews will reassess at daylight for further action. Your safety matters-please respect the 'ROAD CLOSED' signs, and avoid travel in the area! "
Photo: Washington State Department of Transportation Southwest/X

By the numbers: Record daily rainfall amounts were reached across the Pacific Northwest — including at Seattle-Tacoma International Airport, where the NWS' Seattle office said 2.01 inches had fallen and at Olympia Airport, where 2.69" fell.

  • The Stillaguamish River at Arlington "set a preliminarily record of 21.34' feet" around 1:50pm, according to the NWS Seattle.

Meanwhile, Seattle hit a record daily high temperature of 59°F on Tuesday morning.

What's next: The storm will "continue to dump overly abundant moisture" across the region — which, in turn, "will keep the threat for excessive rainfall and flooding elevated" through Thursday, the NWS said.

  • "The majority of the precipitation will decrease by Wednesday night into Thursday, as it shifts eastward throughout the northern Great Basin and northern Rockies, which will allow for heavy mountain snow for many of the elevated ranges."

Between the lines: Climate change is adding even more moisture to atmospheric rivers, enabling them to dump higher rain and snow totals, per Axios' Andrew Freedman.

Flashback: California snowpack reaches all-time high after 17 atmospheric rivers

Editor's note: This article has been updated with new details throughout.

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