673
FXUS66 KPQR 091811
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1011 AM PST Tue Dec 9 2025

.SYNOPSIS...
A prolonged atmospheric river continues to influence the Pacific
Northwest, sustaining periods of heavy rainfall, breezy winds,
and widespread hydrologic concerns through late Wednesday,
possibly as late as early Thursday. Widespread river flooding
remains likely, along with urban and small stream flooding due
to persistent heavy rain. Wind may lead to downed trees and
power outages due to saturated soils.

&&

DISCUSSION...Now through Sunday...Over the past 24 hours,
around 4 to 7 inches of rain has fallen over the north Oregon
Cascades, south Washington Cascades, Willapa Hills, north Oregon
Coast Range, south Washington coast, and northern and central
Oregon coast. About 1.5 to 4.5 inches of rain has fallen over
the Lower Columbia, Cowlitz Valley, and Portland/Vancouver
metro. Refer to the Hydrology section below for river information.

As of 430 AM, precipitation has decreased along the coast but
has increased inland. Around 230 AM to 330 AM, a mesoscale band
of heavy rain moved southward through the Portland/Vancouver
metro. Around 0.20 to 0.40 inch per hour was observed over the
area during that time period, increasing urban flooding and
prompting the issuance of a Flood Advisory. With this mesoscale
band and increasing precipitation inland, the Flood Advisory
will be maintained until 10 AM today.

Attention now turns to the second moisture surge expected to
arrive later this afternoon and persist into Wednesday. IVT
values are projected to be around 600 to 700 kg/ms across
western Washington and far northwest Oregon, suggesting the
strength of the atmospheric river to remain moderate. Given past
observations since Monday, we could see a stronger atmospheric
river. An additional 1 to 2 inches of rain is expected this
morning through Thursday afternoon over the interior lowlands to
the north of Eugene. Around 3.5 to 6.5 inches of additional
rain is expected over the Cascades and coastal mountains, mainly
to the north of Lane County. Given the saturated state of the
soil across the area, this will maintain an elevated threat for
urban, small stream, and river flooding. Landslides in areas of
steep terrain will be possible due to saturated soils, as well
as debris flows over recently burned areas. The focus once again
appears to be northern portions of the forecast area, though
the entire region will experience additional rainfall.

Snow levels remain high, holding near or above 8000 ft through
at least Wednesday, keeping all precipitation as rain in the
Cascades as rain, further contributing to elevated runoff and
river responses. A gradual downward trend in snow levels is
likely late Wednesday night, but too late to influence impacts
during the peak of this event.

Winds remain a secondary hazard but continue to carry relevance
given soil saturation. Overnight gusts generally ranged from 25
to 35 mph across the Advisory area. Similar speeds are expected
again later today as the second surge arrives. Even moderate
gusts may be capable of uprooting trees due to the extremely
saturated ground. Confidence remains moderate to high regarding
scattered tree impacts but low regarding exact location.

The atmospheric river weakens late Wednesday as moisture
transport decreases and the plume begins to dissipate. Showers
will persist into Thursday, though rainfall intensity will be
much lighter and increasingly confined to higher terrain across
southwest Washington and the north Oregon Coast Range. A more
stable pattern develops Friday into Saturday as high pressure
builds, leading to a notable drying trend. Snow levels gradually
lower to around 5500 to 6500 ft through the weekend. Despite
the improving weather, hydrologic impacts for slow- responding
rivers may linger a bit longer. Soils will remain saturated,
particularly across the Coast Range and Cascades, leaving the
region sensitive to additional rainfall.
~12

&&

.HYDROLOGY...
A strong atmospheric river remains in place across southwest
Washington and northwest Oregon this morning, maintaining
an elevated threat of urban, river, and small stream flooding
through at least late Wednesday. Significant rainfall has
already fallen across much of the region since early Monday, and
river responses are now well underway. Additional rainfall
today through Wednesday from the second moisture surge will
prolong elevated flows, with many rivers already exceeding flood
stage, or forecast to exceed flood stage within the next 24-36
hours.

Rainfall over the past 24 to 36 hours has already pushed several
rivers into flood stage, including record flooding on the Grays
River (the old record height was 33.15 ft, which was broken
around 10 PM Monday when river levels peaked around 33.4 ft), major
flooding on the Naselle River, moderate flooding on the Willapa
River, and minor flooding for Nehalem River, Wilson River,
Trask River, Beaver Creek, East Fork Lewis River, Miami River,
and Washougal River. Elsewhere, many basins continue rising and
are expected to respond sharply again as periods of heavy rain
continue. While the Siletz River, Cowlitz River (Kelso and
Castle Rock), and Johnson Creek are currently not in flood
stage or action stage, these rivers are expected to reach minor
flood stage late this morning. Expect the Pudding River to reach
minor flood stage by late Wednesday.

The threat for flooding along small creeks and streams as well
as urban flooding, including roadway flooding, will continue
through Wednesday. Latest high-resolution guidance favors a
band of heavier precipitation lingering over southwestern
Washington and far northwestern Oregon this morning, with rates
around 0.25 inch per hour or higher. These heavy rainfall rates
could make for a hazardous morning commute along the I-5
corridor from Salem north through Portland/Vancouver to
Kelso/Longview with abundant water atop area roadways. Ponding
of water on roads will increase risk of hydroplaning and car
accidents.

Periods of heavy rain will also increase the risk for
landslides in areas of steep terrain and debris flows over
recently burned areas. People, structures, and roads located
below steep slopes, in canyons, and near the mouths of canyons
may be at serious risk from rapidly moving landslides. A Flood
Watch remains in effect across all of southwest Washington and
northwest Oregon from now until 4 PM Thursday, except for most
of Lane County which has been removed from the Flood Watch.

&&


&&

.AVIATION...A mixed bag of LIFR/IFR/MVFR cigs and IFR/MVFR/VFR
visibilities continues across northwest Oregon and southwest
Washington, with cigs and visibilities being lowest from KONP
to KSLE and points north where a large band of steady stratiform
rain continues. Rain will be heavy at times through Tuesday
afternoon, especially during the morning and early afternoon
hours north of KEUG. Rain should finally begin to taper off from
south to north between 06-12z Wednesday as the aforementioned
band of stratiform rain lifts northward over western Washington.

Although winds have become less gusty, occasional wind gusts up
to 20-25 kt are still being observed inland and up to 30 kt at
KONP. Winds will increase along the coast through the day, especially
at KONP where wind gusts will likely approach 35-40 kt. The
remaining TAF sites will see wind gusts increasing late this
afternoon into tonight.

KPDX AND APPROACHES...Expect steady stratiform rain to persist
through at least 00z Wednesday, heavy at times this morning before
rain attempts becoming relatively light this evening. This will
result in development of MVFR cigs between 18-21Z, then
persisting throughout the TAF period, with occasional dips to
IFR possible (20-35% chance) through 00z Wednesday, and then to
60-70% by 01z. Although winds have weakened this morning,
expect winds to increase again towards 02-06z Wednesday when
southerly to southwesterly wind gusts up to 25-30 kt are likely.


&&

.MARINE...Buoy observations from early Tuesday morning showed seas
hovering around 13 to 14 ft with weakening winds. Seas should fall to
12-13 ft by Tuesday afternoon and then remain steady through
Wednesday night. Seas likely fall to 10 ft or lower by Thursday
afternoon. Gale force wind gusts up to 35-40 kt are expected
across the inner waters with the passage of a frontal system late
Tuesday into Wednesday, with gusts up to 30 kt over the outer
waters. That said, gale force wind gusts are likely already
occurring across PZZ253. Gusts will likely peak near 35 kt over
the Columbia River Bar beginning around sunset Tuesday.

Seas and winds will likely fall below small craft advisory criteria
on Friday, with relatively quiet conditions expected over the
coastal waters over the weekend. -23

&&

.BEACH HAZARDS...Buoy observations from early Tuesday morning
showed seas hovering around 13 to 14 ft with weakening winds.
Seas should fall to 12-13 ft by Tuesday afternoon and then
remain steady through Wednesday night. Seas likely fall to 10 ft
or lower by Thursday afternoon. Gale force wind gusts up to
35-40 kt are expected across the inner waters with the passage
of a frontal system late Tuesday into Wednesday, with gusts up
to 30 kt over the outer waters. That said, gale force wind gusts
are likely already occurring across PZZ253. Gusts will likely
peak near 35 kt over the Columbia River Bar beginning around
sunset Tuesday.

Seas and winds will likely fall below small craft advisory criteria
on Friday, with relatively quiet conditions expected over the
coastal waters over the weekend. -23

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Coastal Flood Advisory until 5 PM PST this afternoon for
     ORZ101-102.

WA...Coastal Flood Advisory until 5 PM PST this afternoon for
     WAZ201.

PZ...Small Craft Advisory until 4 PM PST this afternoon for PZZ210-
     251-252.

     Gale Warning from 4 PM this afternoon to 10 PM PST Wednesday
     for PZZ210-251-252.

     Gale Warning until 4 AM PST Wednesday for PZZ253.

     Small Craft Advisory from 4 AM to 10 PM PST Wednesday for
     PZZ253.

     Small Craft Advisory until 10 PM PST Wednesday for PZZ271>273.
&&

$$

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