162
FXUS66 KPQR 081755 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
954 AM PST Mon Dec 8 2025

...Updated hydrology, public, and aviation sections...

.SYNOPSIS...
A prolonged, moisture-rich pattern will hold through midweek as
two significant atmospheric river surges move across the region-
first today, then a secondary and slightly weaker but still
impactful round Tuesday night into Wednesday. The combination of
high-integrated vapor transport, saturated soils, and periods of
stronger winds will sustain the risk for hydrologic issues and
localized wind impacts.

&&

.MORNING UPDATE...The first round of rain from this atmospheric
river event as begun across the Pacific Northwest. Rainfall rates of
0.25-0.40" per hour have been observed this morning across the south
Washington and north Oregon coast, Willapa Hills, and north Oregon
Coast Range. There is high confidence that rainfall rates will hover
between 0.25-0.50" per hour for much of today for these locations.
Rainfall rates this high will result in rivers and creeks draining
off the Willapa Hills and Clatsop and Tillamook Counties to start
rising sharply over the next 2 to 4 hours.    -10

&&

.SHORT TERM...Today through Wednesday...The first of two major
moisture surges is now underway this morning, with the main
plume shifting into western Oregon and southwest Washington. IVT
values today represent the strongest of the week, with ensemble
clusters centering around 750 to 850 kg/ms near the coast and
somewhat lower inland. This deep subtropical feed is producing
widespread rain, and the spatial distribution continues to show
a northward emphasis compared with several days ago. As a
result, rainfall totals today will be highest north of Salem
into southwest Washington, though most areas will see a
substantial increase in runoff as rain falls on very saturated
ground.

Expected rainfall today: 1.25 to 2.25 inches in the Cowlitz
Valley, lower Columbia, Portland/Vancouver metro and northern
Willamette Valley, 0.75 to 1.25 inches in the central Willamette
Valley, and 0.25 to 0.75 inches in the southern Willamette
Valley. Forecast rain amounts reach 3 to 7 inches in the
Cascades, Cascade foothills, Coast Range and the coast, except 1
to 3 inches from Florence to Newport and in areas of higher
terrain in Lane County. Snow levels remain well above 6000 ft,
ensuring all precipitation is rain.

The second major moisture push arrives Tuesday night into
Wednesday. This surge still carries impressive IVT (mean values
around 650 to 750 kg/ms; high-end members approaching 800 kg/ms;
low-end around 550 to 600 kg/ms), though slightly less vigorous
than todays event. Rainfall will remain heavy at times
regardless, prolonging urban and river flooding concerns through
midweek.

Wind concerns increase today and continue through Wednesday.
Monday is expected to be the windiest period, with widespread
confidence in gusts reaching at least 30 mph inland and at least
40 mph along the coast. Given the soils are already saturated
and heavy rain with gusty winds is expected, a Wind Advisory has
been issued for potential impacts and will be in effect from 7
AM today through 4 AM Tuesday. The advisory covers the OR and WA
Coast Range, Willamette Valley from Salem northward through the
Portland/Vancouver Metro, I-5 corridor in WA, and the Cascade
Foothills north of Salem. Soils are deeply saturated, increasing
the likelihood that even moderate gusts could cause uprooting
and damage. While confidence is high in potential impacts,
confidence remains lower in pinpointing exact areas of greatest
wind effects.

.LONG TERM...Wednesday night through Saturday...The atmospheric
river weakens late Wednesday night as the secondary plume
shifts eastward and moisture transport diminishes. However,
residual showers and pockets of moderate rain will persist
through at least early Thursday, prolonging hydrologic
sensitivity. By Thursday into early Friday, the pattern
transitions toward a more typical post-frontal regime with
cooler, showery conditions and decreasing winds. Light rain
returns late Friday into Saturday. Snow levels will gradually
lower into the weekend but remain high enough that little to no
snow accumulation is expected for Cascades through the weekend.
Although overall impacts lessen late week, rivers and soils
will continue responding to the cumulative rainfall load from
this Monday through Wednesday multi-day event.      ~12

&&

.HYDROLOGY...A series of frontal systems will keep conditions
very wet through much of this week. The most notable period
will be today through late Wednesday, when a prolonged
atmospheric river will bring significant rainfall and the
potential for widespread river flooding across southwest
Washington and northwest Oregon. There is a 10% chance for 72
hour total rain amounts up to 6 to 8.5 inches in the Cowlitz
Valley, lower Columbia, Portland/Vancouver metro and northern
Willamette Valley, 4 to 6 inches in the central Willamette
Valley, 3 to 4 inches in the southern Willamette Valley, 7 to
11 inches in the Cascades, Cascade foothills, Coast Range and
the coast, except 3.5 to 7 inches from Florence to Newport and
in areas of higher terrain in Lane County. While rain amounts
this high are unlikely to occur, they represent a reasonable
worst case scenario. This outcome would result in widespread
major flooding.

Although rain will likely become lighter on Thursday, the
threat of flooding will linger along slow responding rivers.
Rivers draining the Coast Range and Willapa Hills have a 40-70%
chance of reaching moderate flood stage and a 20-50% chance of
reaching major flood stage. Additionally, many Willamette River
tributaries that drain from the Coast Range and Cascades have
anywhere from a 40-60% chance of reaching minor flood stage and
a 20-40% chance of reaching moderate flood stage. Flooding of
the Willamette mainstem rivers have a very low chance to occur
(5-15%). Probabilities for specific river points can be found at
the National Water Prediction Service website.

There is also increasing confidence in the potential for
flooding along small creeks and streams as well as urban
flooding, including roadway flooding. 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. Therefore, a Flood Watch remains in effect across
all of southwest Washington and northwest Oregon from now until 4 AM
Friday.

Considering increased confidence and probabilities for flooding of
rivers and urban areas as the forecasted event approaches, Flood
Warnings have been issued for the Grays River at Covered Bridge in
Wahkiakum County, the Wilson River near Tillamook in Tillamook
County, and Johnson Creek at Sycamore in Clackamas and Multnomah
Counties.

Major flood stage at the Grays River is forecast, which will lead to
flooding of lowland areas and roads in the vicinity of Highway 4 and
Rosburg. there will be two peaks for this river. There is high
confidence that the first peak will occur between 1 AM to 4 AM
Tuesday. The river will briefly subside between 4 AM to 10 AM
Tuesday, but a second round of heavy rain will result in another
peak late Tuesday into Wednesday. For the Wilson River, Minor flood
stage is forecast from late tonight to late Wednesday morning, and
for Johnson Creek, Minor flood stage is forecast from Tuesday
morning to Wednesday evening. Both the Wilson River and Johnson
Creek have a 50% chance of reaching Major flood stage. If you know
you live in a flood-prone area, make sure to monitor the latest
weather and river forecasts, and make a plan for potential impacts.

&&

.AVIATION...A moisture-rich frontal system will bring increasing
south to southwest winds across the area today along with a band of
steady rain that will slowly sag southward from northwest Washington
this morning into southwest Washington and most of northwest Oregon
by late morning. Rain will likely take a bit longer to begin at
KEUG. Rain will be heavy at times through the period, lighter around
KEUG. This will result in persistent low-end MVFR cigs with brief
periods of high- end IFR cigs for inland TAF sites, as well as
surface visibility reductions down to 2-4 SM at times. Meanwhile,
persistent LIFR to IFR flight conditions are favored to at the coast
through 12z Tuesday, except through 09z Tuesday at KAST where cigs
will begin lifting to MVFR or low- end VFR thereafter.

Surface wind gusts up to 35-40 kt are expected at the coast, and up
to 25-35 kt within the Willamette Valley. In addition, low level
wind shear will be on the increase at KPDX, KTTD and KAST Monday
morning with 45-55 kt southwest winds at 2000 ft. Note the main
concern is strong speed shear, as winds are nearly unidirectional
from the surface up to 4000 ft, suggesting directional shear will be
minimal.

KPDX AND APPROACHES...Expect mainly low-end MVFR cigs to continue
through 12z Tuesday with a 20-30% chance for cigs to briefly fall
below 1000 ft cigs Monday morning. Steady stratiform will persist
through the period, becoming moderate to heavy at times through the
afternoon. It appears rain will briefly become lighter again Monday
evening before intensifying again Monday night. Expect surface
visibilities down to 2 to 4 SM when rain rates are highest. Wind
gusts up to around 30-35 kt are expected Monday afternoon through
Monday night. Note there will also be a period of increased low-
level wind shear Monday morning as winds at 2000 ft reach 45-55 kt
out of the southwest. The main concern will be strong speed shear,
as directional shear looks minimal.       -19/23

&&

.MARINE...A stronger frontal system is set to arrive early
Monday, bringing gale force wind gusts up to 35-45 kt, strongest
over the inner waters and near the Columbia River Bar. A Gale
Warning is in effect through 1 AM Tuesday as probabilities for gale
force gusts are up to 90%. With the increasing winds, seas will
become steep and hazardous Monday afternoon into Monday night.
Expect seas to peak somewhere between 14 to 17 ft.

Winds decrease from north to south late Monday night into Tuesday
morning with gusts falling below 20 kts everywhere except for
portions of zones PZZ273 and PZZ253 briefly on Tuesday morning.
Then another frontal system moves through the waters Tuesday
afternoon into Wednesday, causing increasing southwesterly winds
with gusts up to 25-30 kt likely. There`s around a 20% chance of
occasional gale force wind gusts over 34 kts across the waters
Tuesday night, though widespread gale force gusts are not expected
for a long enough period of time. One potential exception will be
the inner waters, which have a 30-45% chance of marginal gale force
wind gusts up to 35 kt. Seas also decrease slightly Tuesday into
afternoon Wednesday but remain above 10 ft. Seas and winds subside
late in the week.      -23/03

&&

.BEACH HAZARDS...Tidal overflow flooding around high tide is
likely on Monday, December 8 and possible on Tuesday, December 9.
Despite total tide forecasts decreasing over the coming days, river
levels will be rapidly rising due to a prolonged period of heavy
rain Monday through Wednesday. Confidence has increased that several
rivers along the Oregon Coast north of Lincoln City and the SW
Washington Coast will reach at least 80% of flood flow by high tide
Monday afternoon, when total tide forecasts are expected to peak
near or slightly above 9.5 ft. Therefore, a Coastal Flood Advisory
for tidal overflow remains in effect from 2 PM to 6 PM PST Monday
for these coastal zones. It appears the threat for tidal overflow
flooding is low on Tuesday, as total tide forecasts decrease
considerably and are well below the 9.5 foot threshold.
That said, minor tidal overflow flooding cannot be completely ruled
out for a brief period of time around high tide on Tuesday given
river levels will be running quite high at that time. Will continue
to monitor the tidal and river forecasts for Tuesday.

Additionally, there is 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, waves which can run significantly farther up a beach
than normal, including over rocks and jetties. Sneaker waves can
suddenly knock beachgoers off if 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.     -23/03

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Coastal Flood Advisory from 2 PM this afternoon to 6 PM PST
     this evening for ORZ101-102.

     Wind Advisory until 4 AM PST Tuesday for ORZ104>115-123.

WA...Coastal Flood Advisory from 2 PM this afternoon to 6 PM PST
     this evening for WAZ201.

     Wind Advisory until 4 AM PST Tuesday for WAZ202>208.

PZ...Gale Warning until 1 AM PST Tuesday for PZZ210-251-271.

     Small Craft Advisory from 1 AM to 7 PM PST Tuesday for PZZ210-
     251-271.

     Gale Warning until 7 AM PST Tuesday for PZZ252-253-272-273.

     Small Craft Advisory from 7 AM to 7 PM PST Tuesday for PZZ252-
     253-272-273.

&&

$$

www.weather.gov/portland

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