432
FXUS66 KPQR 020555 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
955 PM PST Mon Dec 1 2025

Updated aviation discussion.

.SYNOPSIS...A series of fronts will bring a wet period of
weather later this week into the weekend across southwest
Washington and northwest Oregon with potentially more impactful
rain next week.

&&

.DISCUSSION...Waver vapor satellite imagery this afternoon
reveals a shortwave ridge of high pressure over the eastern
Pacific. A shortwave trough is dropping southeastward towards
the Pacific Northwest. A mid level front is generating a band of
rain moving southeastward across northwest Washington this
afternoon and could bring a few sprinkles to the northern
portions of the CWA later this evening. Meanwhile, the low
level front is just beginning to push into the Olympic Peninsula.
REFS guidance is in general agreement it will move onto the
south Washington and north Oregon coast late this evening
to around midnight before pushing into the Willamette Valley
late tonight into early Tuesday morning while simultaneously
falling apart. The net result will be a cloudy and in spots
drizzly Tuesday. Light north to northeasterly flow spreads
across the region late Tuesday afternoon into Tuesday night.
This may result in just enough clearing to allow fog and low
clouds to redevelop overnight across inland valleys. The flow
will turn more northwesterly Wednesday and open us to weak
shortwave troughs that could bring light precipitation to mainly
our far northern zones and terrain late Wednesday into early
Thursday.

Models and their ensembles are in good agreement that the upper
level ridge remains over the northeast Pacific on Thursday. WPC
cluster analysis does indicate there is a high probability of
the ridge flattening out, allowing for more westerly flow into
the Pacific NW Friday and into the weekend. This should allow
for frontal systems and attendant atmospheric rivers to bring
increased rainfall and more active weather to the area.
Ensembles are in relatively good agreement, a moderate strength
atmospheric river will spread into the region Friday into early
Saturday bringing with it mainly beneficial rains to the region.
The EC EFI does suggest some notable rainfall amounts will
occur across the Oregon Cascades and foothills Friday night
into Saturday relative to model climatology, but raw ensemble
rainfall amounts appear unlikely to produce impacts with this
first round of rain. With that said, there are handful of the 100
global ensemble members that produce enough rain that our flashiest
rivers would rise sharply and approach minor flood stage Friday
into Saturday, but at this point, confidence remains low in
this scenario panning out based on available ensemble guidance.

Additional rounds of rain will continue for the remainder of
the weekend as ensembles are in general agreement we will remain
under zonal flow in the vicinity of the baroclinic zone. Given
the westerly flow there will likely be periods where the
Willamette Valley rain-shadows out, but it may be raining, at
least lightly, for a significant portion of the weekend across
the terrain, particularly areas farther north in the CWA.
Uncertainty in the forecast details grow significantly early
next week and mainly revolve around whether or not a stronger
atmospheric river with potential impacts to area rivers will
impact the region or not. HEFS guidance does suggest a ~10-15%
chance for rivers like the Willapa, Naselle and Wilson Rivers
to reach minor flood stage at some point in the next 10 days
with that day 8-10 timeframe being the main driver of those
probabilities.

&&

.AVIATION...At 0530z Tuesday, satellite and surface weather
observations depicted mostly cloudy skies across northwest OR and
southwest WA, with cigs ranging between 5000-8000 ft. Expect cigs
to lower to around 3000 ft from north to south between 06-12z
Tuesday, impacting KAST first and KEUG last. While MVFR cigs will
be most predominant tonight through tomorrow morning, cannot
completely rule out a period of IFR cigs below 1000 ft with the
passage of an incoming cold front tonight. This is especially true
at KAST between 09-12z Tuesday when probabilities for cigs below
1000 ft increase to 50-70% with the frontal passage.
Probabilities for cigs below 1000 ft increase to 40-50% at KONP
and to around 20% at KEUG between 13-16z Tuesday, also with the
frontal passage. Light rain showers will also accompany this
frontal passage, albeit with minimal flight impacts.

Expecting predominately MVFR cigs to give way to a mix of high-end
MVFR to low-end VFR cigs towards 22z Tuesday-00z Wednesday. Cloud
cover will likely become more scattered between 03-06z Wednesday
as skies attempt to clear out. This will set the stage for
widespread fog and low stratus development Tuesday night.
Probabilities for surface visibilities below 1/2 SM increase to
50-70% at all inland terminals by 10-13z Wednesday. Fog is much
less likely to occur at the coast where light offshore winds will
help prevent fog development.

KPDX AND APPROACHES...Cigs around 5000 ft should lower to around
3000 ft by 10-12z Tuesday as a cold front moves through the area,
bringing scattered light rain showers with it. Cigs are expected
to trend towards high-end MVFR to low-end VFR thresholds towards
22-23z Tuesday before cloud cover attempts scattering out towards
06z Wednesday. Assuming cloud cover does clear out, fog and low
stratus will become increasingly likely Tuesday night into
Wednesday morning. Probabilities for visibilities under 1/2 SM
increase to around 70% by 10-13z Wednesday at the terminal. -23

&&

.MARINE...Light northeast winds around 10 kt will turn
northwesterly as a frontal boundary approaches from the
northwest. This will increase winds across the waters, mainly the
outer zones north of Cape Foulweather where winds are expected to
reach low end Small Craft Advisory conditions. Winds 15-20 kt with
gusts to 25 kt will be possible from 4 am to 10 pm on Tuesday.
Elsewhere, winds will increase to 10-15 kt with gusts to around 20
kt, staying below Small Craft criteria. A long period, westerly
swell is also expected to move into the waters with heights
increasing towards 10 feet at 15-18 seconds.

Winds and seas ease midweek as high pressure returns. A more
active weather pattern develops late in the week as a series of
frontal systems is expected to moves across the waters from
Thursday into the weekend. There is a 30-60% chance of seas
rising above 10 ft again Saturday into Sunday. /19

&&

.BEACH HAZARDS...A long-period westerly swell is expected along
the northwestern Oregon and southwestern Washington coasts from
late Monday through Wednesday next week. Wave heights increasing
to 8 to 10 ft on Tuesday may not appear to present a safety risk
to those on area beaches, but these energetic waves 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. In addition, a period of perigean spring or "king"
tides means these waves will have an even easier time reaching
high up onto beaches, limiting the areas which may be safe from
wave action.

A Beach Hazards Statement has therefore been issued from 7 AM
Tuesday to 10 PM Wednesday. Sneaker waves can create potentially
life-threatening conditions in the surf zone when beachgoers can
be unexpectedly knocked off their feet and pulled out into cold
ocean waters. Caution should be used when in or near the water,
and those with children should be especially watchful. Never turn
your back on the ocean, and be sure to keep an eye on the waves.
Those participating in razor clam digs should additionally
exercise caution. -36

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 4 AM to 10 PM PST Tuesday for PZZ271-
     272.
&&

$$

www.weather.gov/portland

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