Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1050 AM EST Tue Dec 9 2025
Day 3
Valid 12Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF
NORTHERN IDAHO...

...Northern Idaho and Western Montana...

A double upgrade from no risk area to a Slight Risk was introduced
for a portion of northern Idaho, generally south of I-90 and along
the Montana state line with this update. This upgrade was
introduced largely as a continuation of heavy rain from Wednesday
night across this region. Rainfall rates should be gradually
diminishing through the day Thursday, and as far as the heaviest
rain and immediate impacts, the rain on Wednesday should be more
impactful in this region. However, given the steady rain continues
into the day Thursday, the impacts resulting therefrom should also
continue. Meanwhile further east into Montana, a strong Arctic
front pushing south down the Plains should turn all of the
precipitation over central Montana over to snow. Thus, the flooding
threat is largely confined to northern Idaho and far western
Washington where the warm air associated with the A.R. will remain
in place on Thursday. Rock slides, avalanches, low-lying flooding,
sporadic urban impacts, and very high river levels will all be
ongoing Thursday morning over this area, supporting the Slight Risk
upgrade.

...Western Washington...

A Marginal Risk was expanded mainly for the Thursday morning time
period across much of western Washington with this update. This
expanded Marginal Risk includes the Seattle metro and the Puget
Sound area more broadly. As with further east, it will be a
continuation of the steady rain from Wednesday night into Thursday
across the area. It's likely a Slight Risk upgrade will be needed,
as the rain looks to take its time until Thursday afternoon to
significantly diminish in intensity. The A.R. event broadly will be
diminishing through this period. A large low well out over the
Pacific will take a more northward track, as compared to its
predecessors, as the pattern amplifies. This will effectively cut
off the A.R. as the moisture plume gets directed north towards the
Gulf of Alaska, and therefore, the flow with the A.R. shifts north
into British Columbia and substantially diminishes.

Wegman

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