PROJECT ALERT NOTICE (OR) Atmospheric river event impacting northwest Oregon

Date: Mon, 08 Dec 2025 12:09:25 EST

Summary: An atmospheric river is forecast to bring widespread rainfall from Monday through Thursday, with the heaviest impacts expected in the Greater Portland area and across the northwest Oregon coast.

The Oregon Water Science Center field offices in Portland and the Willamette Valley are preparing to respond to an incoming atmospheric river expected to bring widespread rainfall from Monday through Thursday. Although uncertainty remains, current forecasts indicate likely minor to moderate river, small-stream, and urban flooding across northwest Oregon, including coastal areas and the greater Portland region.

Field staff will be mobilized as needed for streamflow measurements, water-quality sampling, and potential sediment sampling. Additional details on response activities will be provided in future Project Alerts.

All streamgages are currently operational, and more than 10 gages in the area are expected to be affected by flooding. Crew deployment will begin Monday, December 8, with more active response expected Tuesday.