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AGUS74 KWCO 091311
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
700 AM CST TUE DEC 9 2025

.Update...
A very minimal expansion of the Limited impacts area in the northern
Rockies further into western MT was done this morning to account for
excessive runoff potential from the combination of rain and snow melt
through Thursday (Day 3). No changes to the FHO or the messaging for the
ongoing flooding event in WA/OR.

//JEC

Previous Discussion as Follows...

Considerable flooding expected, with landslides possible across portions of
the Pacific Northwest beginning late Monday and will continue through the
week...Rain and snowmelt may generate urban and small stream flooding
across portions of the Northern Rockies this week...

.Pacific Northwest...
A series of frontal systems will bring periods of heavy rainfall through at
least mid-week across western WA and OR with considerable river flooding
and widespread urban and small stream flooding expected. The flooding
impacts will be greatest tonight through Wednesday when the heaviest
rainfall (daily totals of 2 - 5", locally up to 10") is expected. Soils are
saturated and daily rainfall through the week will sufficiently prime the
hydrologic environment. Due to the saturated soils, landslides in the steep
or mountainous terrain are possible mid-week as heavy rainfall lingers
across the region. Widespread minor to scattered major river flooding is
forecast with rapid rises beginning to occur late this evening,
particularly in the foothills of the Cascades and will continue through the
end of the week. Many of the rivers and streams are forecast to experience
multiple peaks throughout the week as multiple rounds of rainfall move
across the basins. While the magnitude and extent of responses continues to
fluctuate somewhat due to the timing of the event, confidence in
Considerable flooding impacts remains high.

.Northern Rockies...
Multiple rounds of rainfall and snowmelt may generate urban and small
stream flooding across portions of northern ID and southwestern MT Monday
night through Thursday. A Limited impacts area persists across this region
given the forecast rainfall and potentially significant amounts of SWE loss
(up to 2") over the next several days.

//KD

Additional National Water Center products are available at
www.weather.gov/owp/operations

$$