385
FXUS66 KPQR 100644 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1044 PM PST Tue Dec 9 2025

Updated aviation and hydrological discussion.

.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.

&&

.SHORT TERM...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 =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 back 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. Recent high resolution models have reduced the
precipitation amounts slightly as the warm front is shifting a
bit further north. Rainfall totals between now and Wednesday at
5 PM, there is around a 50-70% chance of anywhere from 2-32
inches of additional rain in the south Washington Cascade
foothills, 2.5-3.5 inches in the Coast Range north of Tillamook,
and around 0.25-0.5 inch in the Willamette Valley.

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...The atmospheric river continues to push over the
region though it targeting further north than previous forecasts
suggested. Overall a mixture of MVFR and IFR CIGS/VIS with a few
areas of low VFR in the southern Willamette Valley. Winds remain
southerly which will create breezy conditions within the
Willamette Valley and along the coast but will miss the Columbia
River Gorge. One component to note though is the potential for
LLWS at around 2000 ft. This LLWS will be isolated to those areas
moreso sheltered from the surface winds.

Heaviest rain will ease after 12Z Wed however overcast skies still
expected. Models are showing around a 20% chance of IFR conditions
within the central and southern Willamette Valley, around 40%
chance in the central and nearly 100% chance along the coast.
Ultimately will be quite variable and difficult to track.

KPDX AND APPROACHES...Persistent stratiform rain through the next
10 hours with overcast skies through the next 24 hours. Will see
minimal change in category levels though will see fluctuations
within the flight categories. A component to be aware of is the
potential for LLWS. While winds will be elevated around 2000 ft
at KPDX and on the approaches, surface winds were elevated enough
to omit LLWS from the TAF. -27

&&

.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...An atmospheric river remains in place across
southwest Washington and northwest Oregon maintaining an
elevated threat of river, and small stream flooding through at
least Wednesday. Significant rainfall has already fallen across
much of the region since early Monday, but the system is
shifting slightly more north and thus rainfall has begun to
ease. A second round of heavier rain though is expected early
Wednesday morning bringing another surge of water to area
rivers and streams. At this point, rain rates are not expected
to be nearly as robust and thus urban flooding is less of a
risk. 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. Currently, warnings are
in effect for the Grays, Cowlitz, Nehalem, Wilson, Siletz and
the Pudding. The Pudding is a slower responding river and thus
may not see impacts until later Wednesday. Flood Advisories
remain in effect for much of southwest Washington and the north
Oregon Coast.

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. -27

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 10 PM PST Wednesday for ORZ104>115-123.
WA...Wind Advisory until 10 PM PST Wednesday for WAZ202>208.
     Coastal Flood Advisory from 10 AM to 7 PM PST Wednesday for
     WAZ201.
PZ...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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