557
FXUS66 KPQR 202313
AFDPQR

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

.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...Building ridging over the area will keep conditions
dry and partly cloudy over the next 24 hours. Winds are variable
in direction today and will continue to be, lessening overnight.
Generally easterly winds in the north and southerly in the
Willamette Valley. Overnight winds will become light and variable
with a slight northerly track within the southern Willamette
Valley. As is common, ridging behind a low will increase the
probability for widespread fog. In areas that are more fog prone
like KEUG, KHIO, and KUAO expect dense fog. However, easterly
winds along the coast and the Columbia River Gorge may aid in
keeping those areas fog free. Dry conditions on Friday. The burn
off period of fog will be challenging to determine as some areas
will linger longer than others. For example, in the northern
Willamette Valley, high resolution models show the fog dissipating
by 18Z Fri, while in the south it`s closer to 00Z Sat.

KPDX AND APPROACHES...VFR through the next 24-hrs aside from a
30% chance of IFR CIGs after 12Z Fri. At this same time, there is
a 15% chance of VIS of 1/2 mile or less. Probabilities for IFR
conditions are highest on the west side of the terminal. There is
a common trend where the portions of the airport closest to the
I-205 bridge will clear first which likely will be the case Fri
morning. Fog will lift around 18Z Fri if it does form. -27

&&

.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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