353
FXUS66 KPQR 180410 AAB
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
810 PM PST Mon Nov 17 2025

Updated Aviation Discussion

.SYNOPSIS...A brief ridge will bring a period of drier weather
from late Tuesday into early Wednesday before a weakened front
arrives late Wednesday, introducing lowland rain and mountain
snow through early Thursday. Another short-lived ridge builds in
on Friday, followed by a return to showery conditions through
the weekend.

&&

.DISCUSSION...Now through Sunday...Cooler and drier air spreads
across the region today as a shortwave ridge moves overhead,
promoting clearing skies later this evening. Patchy fog will
develop overnight into early Tuesday, although increasing cloud
cover moving in from the northwest late tonight introduces some
uncertainty regarding fog development, especially for southwest
Washington. Another weak shortwave passes Tuesday, bringing
mostly clouds and light precipitation potential, with the best
chances along the north Oregon coast from Tillamook County
northward and across southwest Washington. Rainfall totals
through Tuesday evening have a 20-40% probability of remaining
below one-tenth of an inch.

Snow levels, currently around 3500 to 5500 feet this afternoon,
will fall to approximately 3000 to 3500 feet by late Tuesday
morning before rising again to above 4500 feet by Wednesday
afternoon. Precipitation remains limited for meaningful Cascade
snow through Tuesday. Clearing returns Tuesday night, with an
increasing likelihood of fog; there is a 40-60% chance for
freezing fog in the southern Willamette Valley. Areas of frost
are also possible in the coldest valley locations including the
Hood River Valley, sheltered valleys of the northern Coast
Range, and parts of the southern Willamette Valley. Expect
overnight lows in the 30s, with mid to upper 30s along the coast
and within the Portland/Vancouver metro, and mid to low 30s
elsewhere.

Dry conditions hold through Wednesday afternoon before the next
frontal system moves in late Wednesday into Thursday. Forecast
uncertainty persists regarding whether the approaching trough
will drop south towards California - resulting in weaker
precipitation and a milder cooling trend, or will approach
around the Washington and Oregon border - resulting in a trough
that could bring stronger forcing, colder air aloft, and
broader precipitation coverage. While there is more model
agreement on a solution, location and strength still remains
uncertain. Significant snowfall at the Cascade passes (six
inches or more) remains unlikely at 10% or less, while the
probability for at least one inch of snow is around 25-35% at
Santiam and Willamette Passes and near 10% at Government Camp.
Thursday onward, temperatures remain near or slightly above
seasonal normals, with highs in the low to mid 50s and lows in
the upper 30s to mid 40s through the rest of the week and into
the weekend. A shortwave trough arriving from the northwest on
Saturday brings a renewed chance of lowland rain and mountain
snow, setting up a showery pattern through the weekend. At the
moment, there is only a 5-10% chance for 6 inches or more of
total snow on Sunday. Could see higher chances for 6 inches or
more of total snow at the start of next week. ~12

&&

.AVIATION...As of 04Z Tuesday, satellite and surface weather
observations continue to show VFR flight conditions across the
airspace, with north to northwest winds less than 10 kt. Given
the clearing skies, moist air and light winds, there is a
probability of IFR/LIFR conditions developing within the
Willamette Valley from 12Z-15Z Tuesday with a general 5-10%
probability for most inland locations. However, given the moist
northerly flow expected for KEUG and KHIO, there is a higher
probability (25-40% probability) for IFR/LIFR conditions to
develop. Otherwise, VFR conditions expected to be the predominant
flight category. Any IFR/LIFR conditions that manifest, should
improve to VFR around 17Z-19Z Tuesday. After 19Z Tuesday, VFR
conditions expected to dominate through the remainder of the TAF
period.

KPDX AND APPROACHES...Expect predominately VFR conditions
continue through the TAF period. However, there is a less than 10%
probability of IFR/LIFR conditions developing from 12Z-15Z
Tuesday. Any IFR/LIFR conditions that manifest, should improve to
VFR around 17Z-19Z Tuesday. /42

&&

.MARINE...Buoy observations from early Monday afternoon showed
the continuation of north to northwest winds around 10 to 20 kt,
with seas around 9 to 11 ft at 11 to 13 seconds. Expect seas to
fall below 10 ft across all waters by midnight. Until then,
small craft advisories remain in effect.

A brief reprieve from the active weather is expected Tuesday and
Wednesday as seas subside to 6 to 8 ft at 11-14 seconds. Winds
will also ease while remaining out of the northwest through
Tuesday evening. Winds become northeasterly Tuesday night and
then easterly for a brief period of time Wednesday morning as
offshore flow develops. East winds should generally stay under 10
kt at that time, but may be locally stronger downwind of gaps in
the coastal terrain.

Winds veer to the south Wednesday afternoon and evening as another
frontal system approaches the waters. Wind speeds will also
increase at that time, likely peaking around 15 to 20 kt with
gusts up to 25-30 kt, strongest over the outer waters beyond 10 NM
offshore. Southerly winds should then decrease through the day on
Thursday. That said, a westerly swell will build over the waters
on Thursday despite weakening winds. Seas will most likely become
steep and hazardous Thursday afternoon through Thursday night
with significant wave heights peaking around 14-15 ft with a
dominant wave period around 14-15 seconds. Although this is
currently the most likely outcome, there is still a large degree
of uncertainty. Some wave model guidance shows seas only peaking
around 10 ft or less, while other guidance shows seas peaking near
25 ft. For now, there is a 50% chance seas peak near 14-15 ft,
and a 10% chance seas peak near 20 ft or higher. Given the low
forecast confidence in place on Thursday, have decided to hold
off on issuing a Hazardous Seas Watch for now. -23

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until midnight PST tonight for PZZ210-
     251>253-271>273.
&&

$$

www.weather.gov/portland

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