119
AGUS74 KWCO 152001
HMDNWC

National Hydrologic Discussion - EXPERIMENTAL
NWS National Water Center - Tuscaloosa AL
200 PM CST MON DEC 15 2025

...Considerable river flooding is forecast to return by midweek across
portions of western Washington, with landslides remaining possible...Flash
and urban flooding are possible in American Samoa through Thursday and in
the western islands of Hawaii tonight...Isolated urban and small stream
flooding, along with rock and mudslides, are possible in portions of the
Northern Rockies through Wednesday...

.Washington and Western Oregon...
Additional rounds of rainfall this week from an atmospheric river are
expected to elicit new and renewed rises of moderate and isolated major
river flooding bringing considerable impacts across portions of the western
Cascade foothills in WA. Saturated soils and streams with limited
in-channel storage have created favorable conditions for urban and small
stream flooding, along with the potential for landslides in steep terrain.
While portions of western WA are forecast to reach isolated major flood
stage, this event is anticipated to have less overall impact than the
previous one. Nevertheless, significant river flooding remains possible in
the vulnerable river basins impacted from last weeks historic flooding
event. Elsewhere across the region, the potential for isolated urban, small
stream, and river flooding continues through the week. As the forecast
rainfall begins to sink further south late this week along the western
Oregon coast, minor to moderate river flooding is forecast in basins near
Portland and Salem.

.Northern Rockies...
Moderate to locally heavy rainfall in conjunction with accelerated snowmelt
on saturated soils will maintain the threat of Limited flooding impacts
across portions of the Northern Rockies through Wednesday. Previous rounds
of rainfall have kept the hydrologic systems primed for efficient runoff
and overland flows leading into yet more rainfall. The primary flooding
concern remains urban and small stream flooding, along with the threat for
rock and mudslides in the steep terrains and over burn scars areas. The NWM
along with river flood guidance has been in agreement which has kept the
overall confidence of Limited flooding impacts high for this region.

.American Samoa...
Heavy showers and storms are expected across the islands which may cause
flash and urban flooding impacts through at least Thursday. Low-water
crossing may be at risk and pluvial responses from rapid runoff are
possible.

.Hawaii...
Heavy rainfall is forecast across the western islands of Hawaii through
today which may bring flash and urban flooding impacts. There exists a
potential for long duration rainfall across the islands which will saturate
soils leading to efficient runoff concerns along with the potential for
landslides.

.Northern California...
Rainfall late this week and into the weekend will bring a threat of
localized flooding impacts to portions of NorCal. Topsoils remain normal to
dry and streamflow conditions are around normal, so confidence in
widespread flooding impacts remains low. This area will be excluded from
the FHO selections but will need to be closely monitored for changes to the
forecast.

//JAC

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



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