Hydrologic Outlook

Hydrologic Outlook
ORZ101>128-WAZ201>211-060000-

Hydrologic Outlook
National Weather Service Portland OR
357 AM PST Fri Dec 5 2025

...AN ATMOSPHERIC RIVER WILL BRING PERIODS OF HEAVY RAIN FROM
DECEMBER 8-10, RESULTING IN AN INCREASED RISK FOR RIVER AND URBAN
FLOODING...

A series of frontal systems will keep conditions wet through the
weekend and much of next week. The most notable period will be late
Monday through late Wednesday, where a prolonged atmospheric river
may bring significant rainfall and rising rivers across southwest
Washington and northwest Oregon. Rivers draining the Coast Range and
Willapa Hills have a 10-25% chance of reaching moderate flood stage
and a 8-15% chance of reaching major flood stage. There is also the
potential for flooding along small creeks and streams, as well as
urban flooding. Flooding of the Willamette mainstem rivers is
unlikely to occur (less than 10%). Probabilities for specific river
points can be found at the National Water Prediction Service
website. Periods of heavy rain will also increase the risk for
landslides in areas of steep terrain, and debris flows over recently
burned areas.
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