Two successive atmospheric river pulses are affecting the Pacific Northwest this week, delivering multi-day heavy rainfall and flooding risk across western Washington and northwestern Oregon. The first made landfall early December 9, and a stronger second pulse is forecast to arrive late December 9–early December 10, maintaining high integrated vapor transport and major flood potential through December 11.
Flood watches and warnings were issued across western Oregon and Washington on December 7, 2025, valid through December 12, as strong atmospheric river produces sustained rainfall, rising river levels and increasing landslide risk.
A major atmospheric river (AR4–AR5 possible) is forecast to make landfall over the Pacific Northwest early Monday, December 8, 2025, and persist through Wednesday, December 10, bringing multiple days of heavy rain and elevated snow levels. Ensemble guidance shows ~70–80% of members reaching at least AR4 in southern coastal Washington, with ~20–30% indicating AR5, raising the risk of widespread riverine flooding.
Heavy snow and strong winds are affecting parts of Idaho, Montana, Washington, and Colorado, with multiple winter storm warnings and advisories in effect through Saturday, December 6, 2025. Mountain areas are expected to receive 15–60 cm (6–24 inches) of snow, creating hazardous travel conditions through the weekend.
Three atmospheric rivers (ARs) are forecast to make landfall over the Pacific Northwest (PNW) through December 10, 2025, producing prolonged precipitation and high moisture transport across western Washington and Oregon.
Two weak atmospheric rivers (ARs) are forecast to make landfall over Washington and Oregon between November 25 and 27, 2025, bringing 50–100 mm (2–4 inches) of rain to coastal and mountain areas.
A strong atmospheric river is forecast to move onshore across California through Saturday, November 15, 2025, bringing heavy rain, strong southwest winds, and elevated flash-flood risk across northern, central, and southern parts of the state.
The National Weather Service issued winter weather advisories for the Cascades of Whatcom, Skagit, and western Okanogan counties, Washington, from Wednesday, November 5, through 10:00 PST (18:00 UTC) on Friday, November 7, 2025, as moderate to heavy mountain snow continues.
A Flood Watch is in effect for Mason County, Washington, from Thursday afternoon through Saturday morning, November 6-8, 2025. Due to persistent rain, the Skokomish River is expected to rise above flood stage.
Four back-to-back atmospheric rivers are forecast to make landfall along the U.S. West Coast between November 3 and November 9, 2025. Heavy rainfall totals of 76–130 mm (3–5 inches), with isolated amounts up to 177 mm (7 inches), could lead to localized flooding in parts of northern California and Washington State throughout the week.
