Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
752 PM EST Thu Dec 11 2025

Day 1
Valid 01Z Fri Dec 12 2025 - 12Z Fri Dec 12 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WESTERN WASHINGTON AS WELL AS FOR NORTHERN IDAHO INTO FAR WESTERN
MONTANA...

...Western Washington...

GOES West water vapor imagery showed ridging off of the West Coast
continuing to amplify downstream of an upper level trough/closed
low near 160 W. The result has been a reduction in precipitable
water values and low level winds along the coast of the Pacific
Northwest. IVT values at 00Z ranged from about 250 kg/m/s across
western Washington to ~450 kg/m/s across eastern Washington, and
these values are forecast to continue lowering through 12Z Friday.

Recent hourly rainfall over the upslope regions of western
Washington was generally below 0.10 inches, but isolated pockets of
greater than 0.10 inches in an hour remained across portions of
the southern Cascades. As a warm front located along and west of
the Washington coastline lifts north tonight, the ongoing moisture
axis will also lift north with further weakening of IVT values,
keeping rainfall light but steady into the Coastal Ranges and
Cascades. Peak additional rainfall totals up to 1 inch (perhaps
isolated spots near 1.5 inches) are expected through 12Z.

While the expected overnight rainfall shouldn't amount to a
significant contribution to additional flooding, a Marginal Risk
was maintained given ongoing major flooding across the region and
continued potential for landslides/debris flows within the higher
terrain. Precautions and avoidance of flooded areas should be
taken.

...Northern Idaho and Far Western Montana...

Light to occasionally moderate rainfall is expected to continue
across the northern Rockies of Idaho and Montana overnight.
Westerly flow between 40-50 kt at 700 mb will help contribute to
IVT values initially between 300-450 kg/m/s from eastern
Washington downstream across the Rockies, but weakening to near 300
kg/m/s through 12Z. Rainfall intensities should remain light for
the most part but pockets of moderate rainfall should be expected
overnight and additional peak rainfall totals of 1 to 1.5 inches
are expected through 12Z Friday. The Marginal Risk was maintained
due to ongoing flooding throughout the region and the potential for
additional impacts, although contributions to ongoing flooding
concerns from tonight's rainfall should be minimal.

Otto


Day 2
Valid 12Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 3
Valid 12Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt