884
FXUS66 KPQR 092351
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
351 PM 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 Monday...The strong atmospheric river
(AR) event continues across northwest Oregon and southwest
Washington. Significant rainfall will continue to bring
flooding of rivers, creeks, streams, and other low-lying and
flood-prone locations through at least Wednesday. Concerns for
landslides and debris flows remain as soils remain saturated.

Since midnight on Mon, Dec 8th (the beginning of the event),
weather stations have reported rainfall totals of 4 to 7 inches
across the the north Oregon Coast Range, Willapa Hills, south
Washington Cascades, and north Oregon Cascades, 3 to 5 inches
across the Cowlitz Valley, Clark County lowlands, north Oregon
coast, and south Washington coast, 1 to 2.25 inches across the
central and northern Willamette Valley, and 0.50 to 1 inch in
the southern Willamette Valley.

Moisture from this AR has briefly shifted southward today, with
much of the rain falling across northwest Oregon. Mesoanalysis
as of Tuesday afternoon shows a warm front approaching the
Pacific Northwest, which will gradually shift rain northward
into southwest Washington and far northwest Oregon. This will be
the second round of impactful rain from this AR. The heaviest
rain tonight into early Wednesday morning will be over the Coast
Range, Willapa Hills, south Washington Cascades, and north
Oregon Cascades. Moderate to high confidence (50-70% chance)
that these areas will receive an additional 4 to 6 inches of
rain from this afternoon to 4 AM Thursday, with a 10-20% chance
for locally higher amounts of 7+ inches. This will further
exacerbate flood impacts considering the amount of rain that has
already fallen.

Meanwhile, high resolution guidance suggests a rain shadowing
effect will keep rainfall amounts lower for interior lowland
valleys. Forecast amounts are around 0.10 to 0.25 inches across
the Willamette Valley and most southwest Washington lowlands.
Based on REFS guidance, chances for 0.5 inch of rain or more
across interior valleys are only 5-15%, highest across the
Portland/Vancouver Metro and northern Clark County lowlands. An
exception is the far northern Cowlitz Valley where there is a
50-60% chance for an additional 1 inch of rain of greater north
of Kelso/Longview through Wednesday afternoon.

Snow levels remain high, holding near or above 8000 ft through
at least Wednesday, maintaining rain in the Cascades and
further contributing to elevated runoff and river responses. A
gradual downward trend in snow levels is likely late Wednesday
night.

Winds remain a secondary hazard and continue to carry relevance
given soil saturation. Winds will gradually increase overnight
as this next front moves in. Southwesterly winds will be breezy
with gusts up to 25 to 30 mph for interior valleys, and 35 to 45
mph for across the Coast Range, Willapa Hills, south Washington
Cascades, north Oregon Cascades, and ridgetops surrounding the
Columbia River Gorge. Due to saturated soils, even moderate
wind gusts may be capable of uprooting trees or power lines.
Therefore, a Wind Advisory has been issued for much of northwest
Oregon through Wednesday evening.

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. Additional frontal
system look to arrive early next week.        -10/12

&&

.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...Seas are in the 12-13 ft range this afternoon. Winds,
which died off a bit this morning, are ramping up again this
afternoon and will continue to do so tonight as a stronger
frontal system moves in. This will cause gales (gusts to 40 kt)
and steep to very steep seas over the inner waters into
Wednesday. Gusts of 30 kt are expected over the outer waters
with a low chance (30%) of gale force gusts (35 kt). This
increase in wind could result in significant wave heights
peaking around 14 feet through Wednesday evening. Gales end by
Wednesday evening, but steep seas likely continue, so we`ll
likely need to extend the small craft advisory into Thursday
morning. Seas gradually fall below 10 feet Thursday afternoon
with relatively quiet conditions expected over the coastal
waters Friday and most the weekend. Latest guidance is showing
the next chance for stronger winds and higher seas late Sunday
night into Monday.       -Spilde

&&

.BEACH HAZARDS...Tidal overflow continues to be a threat to the
coastal communities of south Washington, north Oregon and
central Oregon. While tidal stages may be below typical
markers for traditional tidal overflow, the increase in flow of
area rivers increases the probability for overflow. Tidal
overflow concerns remain for this afternoon`s high tide, then
will surge again during Wednesday afternoon`s high tide. The
Toke Point tidal gauge is expected to peak near 9.5 ft around
3-4 PM Wednesday and the Willapa River will likely remain above
80% of flood flow during high tide. Therefore, the Coastal Flood
Advisory has been extended for the high tide on Wednesday.

There remains an elevated threat for sneaker waves late
Wednesday through Thursday along the SW Washington coast south
through the central Oregon coast. The swell period increases to
around 14-15 seconds with swell heights around 9-11 ft, with
swell heights and swell periods decreasing late Thursday night.
This will create energetic waves that will present a moderate to
high risk for sneaker waves, which are waves that can run
significantly farther up a beach than normal, including over
rocks and jetties. Sneaker waves can suddenly knock beachgoers
off of their feet and quickly pull them into the frigid ocean
which may lead to serious injury or drowning. Caution should be
used when in or near the water. Always keep an eye on the waves,
and be especially watchful of children.          -27

&&

.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.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Coastal Flood Advisory until 5 PM PST this afternoon for ORZ101-
     102.

     Wind Advisory until 10 PM PST Wednesday for ORZ104>115-123.

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

     Wind Advisory until 10 PM PST Wednesday for WAZ202>208.

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

     Gale Warning until 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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