Major flooding being unleashed by ongoing atmospheric river in Washington
The second of two atmospheric rivers will unleash many inches of rain and fuel major flooding in parts of western Washington and northern Oregon into Thursday. More storms will follow past the middle of December.
Pouring rain led to widespread flooding in Washington and Oregon on Dec. 9, as rising rivers overwhelmed homes and roads.
Storms lining up over the Pacific are moving inland in the northwestern United States and part of British Columbia, Canada, with copious amounts of moisture, inducing multiple forms of flooding from urban areas to small streams and many of the rivers in Washington, northern Oregon, northern Idaho and western Montana in the coming days.
The rain being produced this week is highlighted by atmospheric rivers, which will bring concentrated heavy rain. A plume of moisture, sometimes referred to as the "Pineapple Express," will extend from west of Hawaii to the northwestern United States into Thursday.
This image of the western and central Pacific, as well as the western part of the United States, was captured on Wednesday, Dec. 10, 2025. A long plume of moisture, or atmospheric river, can be seen from west of Hawaii to onshore in the northwestern part of the U.S. (AccuWeather Enhanced RealVue™ Satellite)
Many low-lying roads along the streams and rivers may be blocked by high water. In some cases, the flooding and mudslide risk may be extreme enough to prompt evacuations. Motorists could experience hazardous travel conditions due to rounds of heavy rain, blowing spray and ponding. Conditions may deteriorate at Seattle-Tacoma International Airport and cause delays.
Nearly every small stream and short-run river in areas of Washington and Oregon will experience flooding.
"Multiple rivers in the Washington Cascades are already at moderate to major flood stage," said AccuWeather Storm Warning Meteorologist Ethan Rogers. "Multiple rivers downstream of Mount Rainier are expected to approach or forecast to break record levels that have not been observed in 75 years for some."
"The Snohomish River at Snohomish, Washington, is forecast to approach the record of 33.5 feet during Thursday night or Friday morning. The gauge at Snohomish has been in service since 1949," AccuWeather Social Media Producer Jesse Ferrell said.
The Skagit River in northwestern Washington is projected to shatter record high water levels by several feet in the coming days. Some of the reliable records along the Skagit River date back to the early 1900s.
"The Grays River at Covered Bridge near Rosburg, Washington, set a new record during Monday night of 33.36 feet," Ferrell added. "The gauge near Rosburg has been in service since 2005 with a previous record of 33.15 feet on Dec. 3, 2007. Several locations along other rivers in the region are forecast to crest within a foot of the record."
A large zone in the Pacific Northwest, including the city of Portland, Oregon, is forecast to receive 4-8 inches of rain from Monday to Wednesday night. Within this zone, there will be pockets where 8-12 inches of rain is in store -- mainly along the west-facing slopes of the Pacific Coast ranges and the Cascades in Washington and northern Oregon. The AccuWeather Local StormMax™ for the first half of this week is 22 inches. Through Tuesday night, Sampede Pass, Washington, has received more than 9 inches of rain, which includes the melted equivalent of snow and sleet since the start of the week.
While December is typically a wet month in the Pacific Northwest, rainfall during the stormy conditions in the weeks ahead may deliver twice the normal monthly rainfall in some cases. Seattle's historical average is 5.72 inches. Rainfall in Astoria, Oregon, averages 10.68 inches. At Stampede Pass, Washington, the average rainfall and melted snow for December is 12.60 inches.
In addition to the flooding threat, road washouts and mudslides are likely as the topsoil becomes saturated and unstable. Debris flows will be most common, but not limited to, areas where wildfires have occurred.
In the highest elevations of the Cascades, where many feet of snow fall and temperatures fluctuate, the risk of avalanches will increase. Fortunately, for motorists heading over the passes, freezing levels will generally remain high enough so that most of the storms this week will bring rain and not snow.
Hurricane Hunter aircraft from the Air Force Reserve's 53rd Weather Reconnaissance Squadron shift their focus during the tropical offseason to investigating the atmospheric rivers. Aircraft are scheduled to investigate the storms this week, according to the latest NOAA schedule.
While a bit of a break or northward shift of the sequence of storms is forecast to occur during the latter part of this week, the storm track will shift farther south once again next week, as the storms will grow larger in size and bring a return of heavy rain (and high-country snow) this weekend to next week.
Until then, a northward bulge in the jet stream will prevail, and that will lead to unusual warmth for the middle part of December along much of the West Coast of the U.S.
Farther inland, the warmth will reach its peak in portions of Montana and Wyoming Wednesday before a press of colder air begins and locally heavy snow develops with possible whiteout conditions on Thursday.
Periodic problems due to flooding and mudslides will continue in the coastal Northwest as rounds of moisture move through the region.
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