893
FXUS66 KPQR 022358
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
358 PM PST Tue Dec 2 2025

.SYNOPSIS...High pressure nudges into the region later tonight
with dry conditions expected on Wednesday. Widespread fog and
frost return tonight through tomorrow morning. A series of
fronts will bring a period of wet weather Thursday through the
weekend across southwest Washington and northwest Oregon with
potentially more impactful rain next week.

&&

.DISCUSSION...Tuesday afternoon through Monday...Satellite
imagery Tuesday afternoon shows low to mid-level clouds across
much of NW Oregon and SW Washington, except for some clearing
occurring in the central and southern Willamette Valley as
northwest flow aloft increases. The few light showers that
linger over the high terrain this afternoon should dissipate by
this evening as high pressure builds overhead and into the
eastern Pacific, with dry weather continuing into Wednesday.
Clearing is expected to continue through the evening hours
across the interior lowlands, and CAMs (HREF and REFS) indicate
this leads to 70-90% chance for low stratus and 50-70% chance
for fog to form late tonight into Wednesday morning across this
area. Additionally, temperatures will be on the colder side
again tonight, falling into the mid to upper 30s across much of
the region except for 40s right along the coast line and 20s
over the Cascades.

Our extended cool and mostly dry weather pattern comes to an end
Thursday as a series of upper level shortwaves and attendant
frontal systems are slated to impact the PacNW into next week.
The parent low- pressure system associated with the frontal
systems impacting the region Thursday into Friday is currently
centered around the Aleutian Islands. This low is funneling
tropical moisture north along the west side of the upper level
ridge, which will then travel over the ridge then south into the
PacNW by Thursday. As the first front moves through the region
Thursday from north to south, IVT values are expected to
increase above 250 kg/m/s. However, the interior valleys will
likely be rainshadowed with not as much rain accumulating,
though the higher elevations and the coast north of Lane County
will likely see steady rain. However, the ridging will begin to
flatten Thursday night into Friday, allowing for more zonal,
westerly flow into the region. Friday is also expected to be
when IVT values peak in the area around 500-750 kg/m/s. These
components together will allow for less rainshadowing in the
interior lowlands with continued steady rain over the terrain
and coast through Friday. As the IVT stream continues into
Saturday, the ridge continues to become zonal, with similar
conditions to Friday. Latest forecast indicates rain totals
from Thursday to Sunday will be around 1-1.5 inches in the
interior lowlands and 1.5-3.5 inches along the coast, Coast
Range, and Cascades. The locations with highest probabilities of
exceeding 3 inches of rain are localized to the Coast Range in
Tillamook County (40-60%) and far north Oregon and SW Washington
Cascades (50-60%). By Sunday, upper level flow is expected to
be completely zonal over the region with another front slated to
move through. This will bring another round of widespread rain.
Overall, widespread flooding impacts are not expected with this
round of rain, though flashier rivers in the Coast Range and
Willapa Hills such as the Grays River near Rosburg and Willapa
River at Willapa could see significant rises if hourly rainfall
rates exceed 0.25-0.3 inches for multiple hours in a row. Will
have more details about potential rainfall rates as we get
closer to this event.

By Monday into the middle of next week, more uncertainty is
introduced in the forecast as ensemble members struggle to
resolve specifics in the pattern. Ultimately, the GEFS and Euro
ensembles both suggest the potential for another atmospheric
river late Monday into Wednesday. However, there is significant
spread in the members between where the strongest band of
moisture will funnel between WA and OR along with the maximum
strength of the IVT values. One thing to note is soils will
already be saturated and river levels elevated from the days of
rain leading up to this event. Depending on the strength of this
this event, flooding could definitely be a concern. HREF
guidance for many rivers indicate a 10-25% chance of certain
rivers reaching action stage and a 5-10% chance for minor flood
stage, mainly focused on the Dec 9-10 time period. Additionally,
there are signals for breezy winds of some sort this the frontal
system associated with this event, although the spread is also
very wide, and if winds do end up even around 30-40 mph,
saturated soils could cause some localized impacts due to downed
trees. Keep in mind there`s still the potential that this event
could be more similar to the lower impact event of this weekend.
It is worth keeping an eye on the forecast as we get closer to
this event. -03

&&

.AVIATION...A mix of VFR and MVFR conditions as the cold front
exits the region and low cloud cover tries to break up. Northerly
winds 5-10 kts become light and variable overnight. Cloud cover
continues to scatter out through the evening and will lead to
widespread fog and low stratus development tonight into Wednesday
morning throughout the Willamette Valley. Probabilities for 1/2SM
or lower visibility are 40-80% by 10-13z Wednesday throughout the
Willamette Valley. Guidance suggests fog and stratus start to
dissipate after 16-19z and VFR conditions should return by late
morning or early afternoon.

KPDX AND APPROACHES...Cloud cover around 1000 feet remains in
place but should break up and lift to low end VFR for a period
this evening. Fog and low stratus become increasingly likely
tonight into Wednesday morning. Probabilities for IFR conditions
increase to around 40-60% by 12z Wednesday. Northwesterly winds
around 5 kt expected through the period. -19

&&

.MARINE...Northerly winds will weaken through the evening,
dropping below 10 kt overnight. A long period westerly swell
moving into the waters will keep wave heights around 8-10 feet
with a period of 14-16 seconds through tonight. Waves drop to
wound 5 feet by late Wednesday and should remain close to this
level through at least Thursday night.

A more active pattern develops later in the week as a series of
frontal systems is expected to move across the waters beginning
Thursday. Winds turn southerly on Thursday with a 30-50% chance
for wind gusts to reach 21 kt, highest probabilities across the
northern waters. Seas expected to remain below 10 feet through
there is a 10-15% chance of greater than 10 feet Saturday morning.
Expect this parade of fronts to continue through the weekend,
with the strongest of the fronts potentially on Sunday.
-19

&&

.BEACH HAZARDS...A long-period westerly swell is expected along
the northwestern Oregon and southwestern Washington coasts through
Wednesday. Waves may run up farther than normal on beaches,
including over rocks, logs, 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
remains in effect through 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.

Additionally, there is a Coastal Flood Advisory for minor tidal
overflow flooding during high tide from 9 AM to 2 PM on Thursday
for the South Washington Coast and the Clatsop County Coast in
Oregon. Minor flooding up to 1 foot above ground level is
possible during high tide in low lying areas near bays, sloughs,
and the low reaches of the coastal rivers. Coastal Residents in
the warned area should remain alert for rising water and take
appropriate action to protect life and property. Remain out of the
water to avoid hazardous swimming conditions. -19

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Coastal Flood Advisory from 9 AM to 2 PM PST Thursday for ORZ101.

WA...Coastal Flood Advisory from 9 AM to 2 PM PST Thursday for WAZ201.

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

     Small Craft Advisory until 10 PM PST this evening for PZZ271-272.
&&

$$

www.weather.gov/portland

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