465
FXUS66 KPQR 012345
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
345 PM PST Mon Dec 1 2025

.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 night into
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.

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...Statistical model guidance suggests there is a
20% chance that IFR to MVFR restrictions return to KEUG later
this evening as low stratus tries to redevelop, but given low
clouds hung on the nearby Coburg Hills, suspect it`s more likely
to happen. A weak front will drop southeastward across
southwest Washington and northwest Oregon overnight. Little in
the way of wind will accompany this front. This will result in a
several hour window where ceilings will have the potential to
lower into IFR and MVFR thresholds as the lower atmosphere
saturates along the coast between 06-12z Tuesday and between
12-18z Tuesday for inland taf sites. Our best statistical model
guidance suggests a 30-50% chance (highest for KAST and lowest
farther south towards KONP) for MVFR restrictions developing at
any given hour in the 06-12z Tuesday timeframe. Probabilities
are more in the 30-40% range for MVFR conditions to develop at
any given hour in the Willamette Valley, primarily in the 12-18z
Tuesday timeframe. The highest chances for IFR conditions will
be at KAST in the 06-12z Tuesday timeframe and climb into the
20-30% range at KEUG and KHIO in the 12-18z Tuesday timeframe
and remain around 10% at other sites like KPDX and KSLE.

KPDX AND APPROACHES...VFR conditions will give way to lowering
ceilings as a weak front slides across the terminal late
tonight into early Tuesday morning. Probabilities for MVFR
ceilings start climbing between 09-12z Tuesday as the front
approaches the region and then peak around 30-40% at any given
hour between 12-18z Tuesday as the front crosses the region. The
probability of IFR conditions developing at any given hour
peaks around 10% between 15-18z Tuesday. The end result is that
conditions will turn a little soupy with flight restrictions
more likely than not, but the main uncertainty revolves around
when exactly these conditions will begin and how long they will
last into Tuesday.

&&

.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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