CW3E AR Update: 8 December 2025 Outlook

December 8, 2025

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Major Atmospheric River to Bring Heavy Rain and Flooding to the Pacific Northwest

An atmospheric river (AR) has made landfall over the Pacific Northwest early today and will continue to impact the region through Thu 11 Dec.
After the initial AR landfall today, a second and potentially stronger pulse of moisture transport will move onshore late Tue 9 Dec/early Wed 10 Dec.
CW3E’s West-WRF ensemble is showing >90% probability of an AR 4 or greater between the Olympic Peninsula and central coastal Oregon, and >50% probability of an AR 5 over much of coastal Washington.
An AR 3/AR 4 is also forecast in the western Cascade foothills and in central Washington and Oregon due to substantial inland penetration of moisture transport.
The NWS Weather Prediction Center (WPC) has issued a slight risk of excessive rainfall across much of western Washington and northwestern Oregon today through early Thu 11 Dec.
More than 10 inches of total precipitation are currently forecast in portions of the Washington Cascades over the next 5 days, with more than 5 inches possible in the lowlands of western Washington.
Multiple days of heavy rainfall and relatively high snow levels will likely result in significant riverine flooding, especially west of the Cascades, where 10 stream gages are currently forecast to reach major flood stage.
While much of the precipitation is expected to fall as rain, areas above 5,000 feet in the Washington Cascades are forecast to receive >2 feet of total snowfall.
As part of the CW3E-led Atmospheric River Reconnaissance program, flights are being planned and conducted to sample this AR in partnership with the US Air Force 53rd Weather Reconnaissance Squadron.