Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
241 PM 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...

...2000 UTC Update...
Trimmed a little bit of the Slight Risk area on the western slopes
of the Cascades (above 3500 ft) due to the lowering snow levels
with time during the period. Otherwise, also made minor adjustments
to the Marginal Risk area over northeast WA-northern ID-northwest
MT, based on the new (12Z) guidance QPFs and HREF exceedance
probabilities.

Hurley

...Previous discussion...
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