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AGUS74 KWCO 061244
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
644 AM CST SAT DEC 6 2025

.Update...
The overall forecast has not changed substantially with widespread flooding
impacts still anticipated during the upcoming week in the Pacific
Northwest, however per coordination with local NWS offices, the
Considerable and Limited impact areas have both been adjusted this morning.
The considerable area has been extended to cover much of northwest WA
(western drainage of the Cascades) and down to Puget Sound, including the
Chehalis/Lower Columbia Basin. The Limited impacts area was extended to the
WA coast and further south through Eugene, OR. Timing for both categories
was changed from "Days 4 - 7" to "Through Day 7", as impacts are expected
to begin Sunday night (Day 2) into Monday (Day 3).

//JEC

Previous Discussion as Follows...

Considerable flooding across portions of the Pacific Northwest beginning
late Monday and may linger through the week...

.Pacific Northwest...
A series of frontal systems will bring periods of heavy rainfall through at
least the middle of next week across western WA and OR with considerable
river flooding and urban flooding becoming increasingly likely. The
flooding impacts will be greatest on Monday evening through Wednesday of
next week when the heaviest rainfall (daily totals of 2 - 4") are expected.
Soils are wet following waves of precipitation over the past several weeks,
and daily rainfall through next week will sufficiently prime the hydrologic
environment. Minor to isolated major river flooding is forecast with peaks
beginning to occur late Monday evening, particularly in the foothills of
the Cascades and may continue through late next week. Fortunately, snow
levels are expected to remain in the higher elevations limiting the overall
snowmelt runoff component. Regardless, the magnitude and extent of
streamflow and river responses has increased which has increased our
confidence in Considerable flooding impacts. Model guidance has suggested
some southward expansion in the precipitation pattern so this area will
need to be closely monitored as the situation evolves over the weekend.

//JAC

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

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