163
FXUS66 KPQR 190600
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1000 PM PST Tue Nov 18 2025

.UPDATED AVIATION DISCUSSION...


.SYNOPSIS...A weakening frontal band is sliding slowly eastward
through the forecast area this afternoon, producing widespread
mid-level cloud cover and virga. Precipitation reaching the
ground has been extremely limited, and dry conditions will
prevail for most locations. After a brief interruption Wednesday
night into Thursday with a weak front brushing the region, a
broader transition toward a wetter, more active pattern takes
shape over the weekend and into early next week.

&&

.SHORT TERM...Now through Thursday Night...The frontal zone
draped from the north Oregon Coast toward southwest Washington
continues to drift inland. There continues to be little to no
precipitation from this frontal band as most of the moisture
continues to evaporate within the sub-cloud layer. The trailing
edge of the band now stretches from roughly Tillamook northeast
to Kelso, and this feature will exit over the Cascades by late
this evening.

Temperatures will hold near seasonal norms through this
afternoon, but the combination of clearing tendencies and a
drier air mass tonight favors stronger radiational cooling.
Early this morning, a brief period of freezing fog developed in
the Eugene area, and the pattern tonight points to a
similar a similar risk for the southern Willamette Valley. Fog
potential overall is higher tonight than last night, especially
for Salem southward. Could see pockets of dense fog elsewhere
in interior valleys before sunrise Wednesday morning. Easterly
winds within the Columbia River Gorge and along the coast will
likely keep fog out of nearby terminals, although fog being
advected within the Columbia River Gorge towards Troutdale and
Portland is not out of the question.


Wednesday will remain largely quiet, with temperatures a few
degrees warmer than today. The next system arrives late
Wednesday as a modest shortwave and surface front approach from
the Northeast Pacific. Model consensus continues to show the
upper trough splitting, but with the main closed low
heading northeastward towards Juneau AK and a small shortwave
trough that may form a small closed surface low drifts eastward
towards the Pacific Northwest. Uncertainty remains regarding the
location of the shortwave trough as it moves towards the PNW, as
models suggest that it will move into either Washington or
Oregon. This system will bring around 0.20 to 0.40 inches of
rain to the coast and Coast Range, 0.10 to 0.20 inches within
the interior valley, and 0.10 to 0.30 inches along the Cascades
and Cascade foothills, with the higher amounts expected along
the central Oregon Coast and Coast Range. Snow levels will stay
above 5000 feet, keeping travel over the Cascade passes largely
unaffected.

.LONG TERM...Friday through Tuesday Morning...The end of the
workweek begins under a broad but low-amplitude ridge, keeping
the primary storm track pointed into British Columbia on Friday,
focusing the better rain chances over western Washington and
brushing only the far northern portions of our region. Farther
south, shower chances remain lower but not zero as weak
disturbances pass along the periphery of the ridge.

Over the weekend, the ridge axis shifts inland and gradually
breaks down as a series of Pacific waves drop southward.
Ensemble guidance has grown more aligned in showing the storm
track dipping south into Oregon by Sunday, introducing a
steadily increasing probability of widespread rain. Confidence
is higher for a more organized system late Sunday into Monday,
which could deliver meaningful precipitation to the lowlands and
accumulating snow to the Cascades. Cooling aloft within the
approaching trough supports falling snow levels, and current
probabilities show a 25-35% chance for at least 6 inches of new
snow at the Cascade passes from late Sunday into early Tuesday
morning.
~12


&&

.AVIATION...Tonight high pressure will maintain calm winds and
mostly clear skies setting the stage for widespread fog and low
cloud development resulting in degraded flight conditions through
much of Tuesday morning. Currently as of ~05-06z, CIGs/VIS have
already begun to lower across the central and southern Willamette
valley with more localized pockets of fog elsewhere into the
Portland Metro and in coast range/Cascade valleys. High confidence
(70-90%)in the continuation of this trend towards IFR/LIFR
conditions for most inland sites by 08-11z, including KPDX. The
REFS which has captured fog development well thus far projects a
~70-80% chance for <0.5 mile VIS for all inland terminals
excluding KTTD by 12z. It`s this latter site (KTTD) and coastal
sites outside of well protected valleys (KONP, and to some extent
KAST) where forecast confidence is lower due to the development of
easterly flow as the night goes on which would limit fog/low
stratus formation where it can surface. Still, would give KTTD a
40-50% chance for IFR to LIFR conditions between 09-13z before
those east winds become more prominent. It`s also worth noting
temperatures will be right around 32 degrees at KEUG by sunrise,
meaning freezing fog is possible.

East flow and added mixing as the morning goes on will chip away
at the fog/low stratus largely N to S through the Willamette
Valley but will struggle to scour out the airmass KSLE to KEUG.
Forecast confidence regarding the timing of any categorical
improvement through Wednesday morning into the afternoon is low.
That said, expect breezy east wind with gusts up 20-30 knots to
develop at KTTD by 16-18z.

KPDX AND APPROACHES...Fog is currently attempting to develop
around the terminal late this evening as confidence grows in a
drop to IFR/LIFR conditions around 08-10z with a probabilities
peaking at 75% for <0.5mile vis around 12-13z Wednesday.
Confidence is still rather low as to exactly when fog and low
stratus will scour out at the KPDX terminal, as the terminal
will be near the edge of the stratus/fog deck. The end time
depends solely on when easterly winds reach the KPDX terminal.
Current guidance suggests the earliest this occurs would be
around ~15z Wednesday but they tend to progress too quickly in
these scenarios. Higher confidence in a return to VFR by
18-21z.
-99

&&

.MARINE...
Buoy observations from Tuesday afternoon showed seas
ranging between 6 to 8 ft at 11 to 12 seconds, with light north to
northeast winds around 10 kt. Winds are still expected to become
easterly for a brief period of time Wednesday morning as offshore
flow develops. East winds should generally stay at or under 10
kt, but may be locally stronger downwind of coastal gaps. Winds
veer to the south and increase Wednesday afternoon as another
frontal system approaches the waters, with wind gusts peaking
between 25 and 30 kt Wednesday evening through Wednesday night as
the front moves through. Small Craft Advisories have been issued
to cover this threat.

Winds weaken significantly on Thursday behind the frontal passage,
however a long period westerly swell will be rapidly increasing.
Forecast seas have increased with today`s forecast update, and are
now expected to peak between 17-19 ft Thursday afternoon and
evening with a dominant wave period of 14-15 seconds. There is a
10% chance seas will peak at or slightly above 20 ft. Given
increasing confidence for steep and hazardous seas on Thursday, a
Hazardous Seas Watch has been issued for the inner and outer
waters late Thursday morning through Thursday night.

Seas are then expected to slowly subside to 10-13 ft Friday
morning and afternoon, and then remain within that range through
the upcoming weekend. Winds look to stay under 20 kt Friday
through the weekend as well. -23

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory from 7 PM Wednesday to 10 AM PST Thursday
     for PZZ251>253.
     Hazardous Seas Watch from Thursday morning through late
     Thursday night for PZZ251>253-271>273.
     Small Craft Advisory from 2 PM Wednesday to 10 AM PST Thursday
     for PZZ271>273.
&&

$$

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