Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
321 AM EST Sun Dec 14 2025
Day 2
Valid 12Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER WESTERN
WASHINGTON AND NORTHWEST OREGON...

Areal coverage of rainfall expands and rain rates increase on
Monday as a well defined atmospheric river continues to direct
abundant moisture into the Washington coastal ranges and Cascades.
IVT values approaching 800 is currently forecast along or near the
Washington coast as the Day 2 period begins...then weakens
somewhat as the axis progresses southward into Oregon. Given
antecedent conditions from the excessive rainfall event from
earlier in the week plus whatever falls on in the Day 1
period...the concern is for renewed flooding potential in addition
to worsening any on- going flooding. Given how water-logged the
soils have been...the potential is there for additional landslides
or mudslides. Saw little reason to modify the Slight risk area too
much...but continued the idea from yesterday in shrinking the
Slight risk area to minimize the overlap with heavy snow areas
(especially in the northern part of the Cascades as depicted by the
WPC Winter Weather desk). That being said...the overall forecast
reasoning changed little given the consistent magnitude of the
IVT/precipitable water values and QPF forecast by the global
models. The focus of the heavy rainfall should gradually shift
southward into an area that did not receive as much rainfall from
the previous atmospheric river.

Introduced a Marginal Risk area mainly focused over the Idaho
panhandle and a small portion of neighboring eastern Washington
mainly for later in the period. The Atmospheric River moisture
plume will be spreading increasing amounts of moisture into the
eastern part of Washington and northern Idaho. Deterministic QPF
approaching an inch is forecast for areas that had hydrologic
problems recently and concern is for additional problems.

Bann

Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt