290
FXUS66 KPQR 201201
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
401 AM PST Thu Nov 20 2025

.SYNOPSIS...Largely dry weather is expected into the weekend,
however a pattern shift early next week will favor conditions
turning colder and wetter.

&&

.SHORT TERM...Now through Saturday Night...A frontal rain band
remain draped across much of the region early this morning,
although the latest satellite imagery does show post-frontal
clearing along the central Oregon coast as the remaining area of
precipitation lifts to the northeast. Meanwhile, water vapor
imagery shows the elongated parent trough pinching off to form
a closed upper low offshore. As this low makes its closest
approach this morning before diving south into California, some
lingering light rain showers may continue west of the Cascades.
By this afternoon, those chances will be limited just to coastal
areas, before the drying trend continues into tonight. Rainfall
totals are expected to remain light, namely 0.05-0.15 inches
across interior lowlands and 0.25-0.5 inches along the coast,
although locally higher amounts of up to an inch are possible in
the central Oregon Coast Range. Snow levels dropping below 4000
ft through today will support light snow accumulations at the
Cascade passes, most likely of an inch or less before shower
coverage diminishes by the early afternoon.

As the aforementioned cutoff low dips into California, broad but
low-amplitude upper-level ridging will develop over the western
half of the country, supporting a drier stretch of weather into
this weekend. Overnight clearing will yield efficient radiative
cooling and valley fog development both tonight and tomorrow
night, most likely in the Willamette Valley and other sheltered
valleys in the Coast Range. Areas of frost are more likely to
develop where temperatures are cold enough in the Cascade
foothills and atop some of the higher peaks of the Coast Range.

With the ridge axis nearly overhead at the end of the workweek,
shortwaves moving along the strong track will largely remain
to the north in British Columbia and northwestern Washington.
Despite this, there will still be 30-50% chances of light rain
showers reaching the southern Washington coast on Friday,
spreading to the remainder of southwestern Washington and the
northern Oregon coast on Saturday as ridging shifts east. -36


.LONG TERM...Sunday through Wednesday...As the upper-level ridge
axis moves east of the Rockies and troughing settles in over the
Pacific Northwest, ensemble guidance continues to come into
better agreement on the timing of precipitation onset, with the
vast majority of their membership bringing rain into the region
late Sunday into Monday. As such, chances for rainfall increase
quickly through the day on Sunday. Given antecedent ridging,
snow levels look to remain above 6000 ft as this system arrives,
but drop to 2000-3000 ft by the time precipitation winds down
late Monday. This may allow for some light snow accumulations at
the Cascade passes, however chances for more significant snow
totals of 6 or more inches at pass-level remain low, about 10%.
Conditions then trend drier on Tuesday.

Looking toward the middle of the week and the Thanksgiving
travel period, there is a notable chance, about 50%, of at
least a weak atmospheric river directed at the central or
northern Oregon coast. Whether this feature will translate to a
significant precipitation forecast remains to be seen. -36

&&

.AVIATION...A frontal boundary has begun to exit eastward early
this morning. While the most persistent area of rain showers is
largely to the north/east of area terminals, lingering light
showers remain possible until the early afternoon, 21-24z Thu.
Latest satellite imagery shows a narrow region of clearing skies
currently extending from KEUG toward KTMK. Given earlier rain,
this cloud break could provide an opportunity for IFR conditions
to develop within fog or mist before sunrise, most likely near
KEUG. Otherwise, mixed VFR/MVFR conditions should trend to VFR by
midday as cigs lift to 4-5 kft, however confidence remains only
moderate in the timing of improving cigs. As the frontal system
exits the region, skies will clear after 00z Fri, with more
widespread fog at inland terminals possible by 06-09z Fri.

KPDX AND APPROACHES...MVFR/low-end VFR conditions are likely to
continue this morning, with an improvement toward VFR expected by
16-18z Thu as cigs lift, although confidence is not high in the
timing. There remains a low chance, 10-15%, of brief IFR cigs
within a more significant rain shower, but those chances will drop
toward zero after sunrise. Isolated showers may persist through
21-24z Thu before skies trend much clearer this evening. Chances
for IFR fog increase after 06-09z Fri. -36

&&

.MARINE...Southerly to southwesterly winds have begun to ease
below 10-15 kt in the wake of an earlier frontal passage, although
a few wind gusts in excess of 20 kt may yet occur in the next few
hours through sunrise, most likely over the inner waters. Seas,
however, will rise above 10 ft this morning as a long-period
westerly swell arrives. This swell will see seas rapidly rise to
16-19 ft at 14-15 seconds by this afternoon and evening. Small
Craft Advisories in effect across the waters will transition to
Hazardous Seas Warnings from 10 AM today through 4 AM Friday,
spanning the time when seas are expected to be at or above 15 ft.
Additionally, a strong ebb tide across the Columbia River Bar at
428 PM today will exacerbate hazardous conditions, resulting in
seas of 13-16 ft. A Hazardous Seas Warning will also therefore be
in effect for the Columbia River Bar this afternoon into tonight.

While seas will ease below 15 ft by early Friday morning, the
long-period swell will persist through the weekend. 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. -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 from 10 AM this morning to 4 AM PST
     Friday for PZZ210-251>253-271>273.

     Small Craft Advisory until 10 AM PST this morning for
     PZZ251>253-271>273.

&&

$$

www.weather.gov/portland

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