970
FXUS66 KPQR 210538
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
938 PM PST Thu Nov 20 2025

.UPDATED AVIATION DISCUSSION...

&&

.SYNOPSIS...Largely dry weather is expected into the weekend,
with foggy and frosty mornings. A pattern shift early next week
will favor conditions turning wetter.

&&

.DISCUSSION...Thursday afternoon through Wednesday night...
Weak high pressure is building over the eastern Pacific this
afternoon and will continue building northeast over NW Oregon
and SW Washington tonight into Friday. Partly cloudy skies can
be observed on visible satellite imagery this afternoon. Skies
will continue to clear by the evening hours before the high
pressure overhead will allow for sufficient radiative cooling to
result in widespread fog or low stratus development across much
of the Willamette Valley late tonight through Friday morning,
clearing by early Friday afternoon. Additionally, temperatures
tonight will be quite chilly, falling into the 30s across the
majority of the lowlands, with frost likely across much of the
interior lowlands. As the ridge continues building inland
tomorrow into Saturday, expect a rinse and repeat for most
locations of overnight and morning fog and frost. However, some
locations may not break out of the fog at all Friday afternoon
or Saturday afternoon, especially in the southern Willamette
Valley where very light winds will allow fog to become trapped.
These locations may see high temperatures each day only in the
40s as the clouds will limit surface heating.

Ensemble guidance continues coming into better agreement that
ridging will become more zonal on Saturday. A frontal system is
expected to move into the Vancouver Island region with a cold
front stretching from Vancouver Island well southwest into the
eastern Pacific, nearly stalling here through the day on
Saturday with a weak warm front approaching the WA coast. This
would funnel a stream of moisture into the WA and northern OR
coast with a 30-60% chance of rain showers hovering in this
region through the day Saturday. Elsewhere is expected to remain
dry. An upper trough approaches the coast late Saturday into
Sunday, finally pushing the frontal system east, bringing a
round of widespread rain through the region Sunday with
scattered showers continuing into Monday. Rain amounts will once
again be on a low side with 0.30-0.9 inches along the coast and
terrain and 0.15-0.40 inches for the inland valleys.

Colder air will funnel into the region behind this frontal
system for Sunday night into Monday night, especially as
transient high pressure builds over the eastern Pacific and
along the coast into Tuesday. Another round of frosty overnight
conditions is possible with 50-80% chance of morning low
temperatures falling below 36 degrees, highest chances Monday
night into Tuesday morning. Daytime temperatures on Tuesday also
look to be on the chilly side with inland locations struggling
to reach 50 degrees.

In terms of precipitation, guidance becomes more uncertain
Tuesday and beyond. Some ensembles indicate a weak weather
system could undercut the ridging sometime on Tuesday or
Wednesday, leading to increasing precipitation chances. With the
cold air still in place Tuesday morning, forecast morning
temperatures near freezing in the southern Willamette Valley.
This combined with a 15-20% chance of rain in the area is
leading to a mention of a mix of rain and snow in the forecast.
However, probabilities for any accumulating snow (greater than
0.01 inch) are near zero, so if any snow does fall, it would be
flurries or slushy rain. Then, ensemble members are in better
agreement of another weather system approaching the area
sometime Wednesday into Friday, bringing another round of
precipitation, though confidence is low on exact timing and
amounts. There`s around a 50-70% chance of a weak atmospheric
river associated with this weather system, so keep an eye on the
forecast if you have travel plans around the holiday. -03


&&

.AVIATION...Late this evening a ridge of high pressure continues
to build overhead with dry conditions taking hold across the
region. However the combination of partial clearing, lighter
winds, and ample surface moisture likely supports ample fog
development headed into the sunrise hours, especially for more
fog prone like KEUG, KHIO, and KUAO. In this regards KEUG has
already dropped to IFR conditions as of 04-05z. We`ll have to keep
an eye on light persistent easterly winds along the coast and far
western the Columbia River Gorge which may aid in keeping those
areas(like KTTD) fog free. Still, even for these spots it`ll be a
close call for either fog or low stratus come sunrise. Headed
through Friday morning the burn off period for fog will be
challenging as some areas will see lingering degraded linger
longer than others, particularly in the Tualatin Valley and
central/south Willamette valley. The latest 00z high resolution
models show the fog dissipating around ~18-22Z Fri for these
aforementioned areas but models often scour out the fog and low
clouds too quickly in these setups. There`s a decent chance
(40-50%) KEUG doesn`t clear out at all Friday. Looking just
outside of the TAF period, it`s worth highlighting there is high
confidence in another round of dense fog/low clouds for the
Willamette Valley Friday night into Saturday.


KPDX AND APPROACHES...Expect VFR conditions to persist the next
several hours into early Friday morning. However, chances for a
period of degraded conditions due to fog are increasing with a
50-65% chance for IFR CIGs/VIS between 13-16z after which point
we`ll likely see improvement back to VFR. Due to weak easterly
flow through the Gorge, portions of the airport closest to the
I-205 bridge will most likely clear first Friday morning. Winds
stay fairly light through the TAF period, generally less than 5-8
knots. -99

&&

.MARINE...Winds have eased and seas are beginning to amplify.
Currently seas have been slower to respond, but buoy 46089 is
showing seas of 19 ft and increasing. However, these heights
have not been replicated in the inner waters. Seas of 8-11 ft at
14 seconds are being observed but should increase over the next
several hours. With the later start time, there may be a longer
period of Hazardous Seas that extends beyond 4 AM Fri. Have
issued a Small Craft advisory for seas on the back end of the
Hazardous Seas Warning due to elevated seas just below criteria.


Seas will therefore remain at 10-13 ft until Monday, a
considerable duration of conditions hazardous to small craft.
Winds, meanwhile, will remain generally out of the south at 10-15
kt through Saturday night, before increasing and turning out of
the northwest as a frontal system crosses the waters Sunday into
Monday. -27/36

&&

.BEACH HAZARDS...An energetic westerly swell is expected along
the northwestern Oregon and southwestern Washington coasts for a
long duration from Thursday through next Monday. Initially, the
swell will reach 15-18 ft at 15 seconds through much of
Thursday, before weakening slightly to 10-12 ft at 12-15 seconds
from early Friday afternoon through the the weekend. Even when
this swell is slightly lower amplitude, its long-period nature
will yield a high risk for sneaker waves along area beaches.
These energetic waves can run significantly farther up a beach
than normal, including over rocks and jetties, creating
potentially life-threatening conditions in the surf zone when
beachgoers can be unexpectedly knocked off their feet and pulled
out into cold ocean waters.

A Beach Hazards Statement has therefore been issued from 5 AM
Thursday through 5 AM Monday. Caution should be used when in or
near the water, and beachgoers 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...Hazardous Seas Warning until 4 AM PST Friday for PZZ210-
     251>253-271>273.
     Small Craft Advisory from 4 AM to 10 AM PST Friday for PZZ210.
     Small Craft Advisory from 4 AM Friday to 4 AM PST Saturday for
     PZZ251>253-271>273.
&&

$$

www.weather.gov/portland

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