121
FXUS66 KPQR 181808 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1008 AM PST Tue Nov 18 2025

Updated aviation discussion.

.SYNOPSIS...Largely dry weather through Thursday night aside
from a weak front bringing light rain Wednesday night into early
Thursday. The pattern shifts wetter by the end of the workweek
as a more potent system could bring more widespread lowland rain
and mountain snow late this weekend or early next week.

&&

.SHORT TERM...Now through Thursday Night...A weak upper-level
trough and associated mid-level cold pool will pass overhead
through today, however little in the way of precipitation is
expected. Rainfall of less than 0.1" is most likely along the
Oregon Coast north of Tillamook and Long Beach Peninsula of
Washington, as well as inland through the Willapa Hills and
southern Washington Cascades. While snow levels are low, only
3500-4000 ft, very low precipitation amounts will translate to a
few tenths of an inch of snow, at most.

Dry conditions are otherwise expected across the region, with
near-normal afternoon high temperatures in the upper 40s to low
50s for most today trending 3-5 degrees warmer by Thursday. The
most noticeable sensible weather of the next couple days will be
cold overnight temperatures some 5 degrees or so below normal.
Wednesday will likely feature the coldest morning of the season
so far for most, with temperatures around sunrise in the low to
mid 30s. Widespread frost is possible in the coldest areas,
however patchy fog may also form before temperatures fall enough
to yield frost, instead keeping lows a few degrees warmer by
limiting additional radiative cooling. Regardless, a true fall
chill will be in the air mornings through midweek.

Early Thursday morning, another trough and associated surface
front will approach the coast from the west. Much like other
weak troughs that have neared the region over the last week,
the bottom of the trough looks likely to pinch off into a closed
upper low which will sink southward into California while the
rump trough to the north weakens as it moves onshore. The net
result locally is relatively weak forcing for ascent and
therefore generally light rainfall totals across the region. The
highest amounts will be nearer to the upper low, namely across
the central Oregon Coast and areas west to the Cascades, where
0.1-0.4" of rain is forecast. Elsewhere in interior portions of
northwestern Oregon north of Lane County, along the north Oregon
coast, and across much of southwestern Washington, rain of up
to 0.15" is expected. Snow levels will generally remain above
5000 ft through this event, limiting impacts at the passes. -36


.LONG TERM...Friday through Monday...While another upper low
dives southward into southern California, very low amplitude
ridging will be centered over the Pacific Northwest. This will
place the mid-latitude jet and resultant storm track pointed
into Vancouver Island. As shortwave impulses approach the coast,
this will keep persistent chances of rain in western Washington
with lower chances extending south into western Oregon. Ensemble
guidance is in fairly good agreement that the storm track will
sag southward as the upper ridge axis shifts inland through the
weekend, bringing increased chances for precipitation to the
region especially through Sunday and Monday. As snow levels fall
due to cold air within any troughing, impactful mountain snows
remain possible by next Monday, with a 35-45% chance for 6" of
snow at the Cascade passes through 4 AM Tuesday. -36

&&

.AVIATION...High pressure will maintain calm winds across the area
throughout the TAF period, except around 15-18z Wednesday when
easterly winds will develop at KTTD and KPDX, beginning at KTTD
first and KPDX last. High clouds this morning will push east of
the Cascades between 00-03z Wednesday, while cloud cover clears
out west of the Cascades. This will set the stage for fog and low
stratus to develop across much of the Willamette Valley between
06-12z Wednesday, likely impacting all inland terminals. The
exception is at KTTD where easterly winds should prevent fog from
developing. KPDX will likely be near the edge of the fog/low
stratus deck, but suspect visibilities at KPDX will fall to 1 SM
or lower by 09-10z Wednesday before fog scours out by 17-18z
Wednesday as east winds reach the terminal. There is a 50-75%
chance for dense fog reducing surface visibilities to 1/4 SM at
KEUG, KSLE, and KUAO. Probabilities are lower at KHIO at 10%, but
feel these probabilities are misleadingly low given the clear
skies and calm winds in place this evening and with KHIO being a
fog-prone TAF site. Also worth noting is temperatures will be
right around 32 degrees at KEUG when fog develops, meaning
freezing fog is possible.

KPDX AND APPROACHES...VFR flight conditions will persist through
approximately 09z Wednesday. Clearing skies after 00z Wednesday
with calm winds will favor fog and low stratus development after
09z Wednesday, with surface visibilities likely falling to 1 SM or
lower. There is a 30% chance visibilities will fall as low as 1/4
SM. Confidence is rather low regarding the exact time fog and low
stratus will scour out at the KPDX terminal, as the terminal will
be near the edge of the stratus/fog deck and the end time will
depend on when easterly winds reach the KPDX terminal. Latest
guidance suggests east winds will finally reach the KPDX terminal
around 17-18z Wednesday, which is when fog and low clouds are
expected to scour out. -23

&&

.MARINE...A brief reprieve from active weather is expected
Tuesday and Wednesday as seas subside to 6-8 ft at 12-13 seconds.
Winds will also ease while remaining out of the northwest through
Tuesday evening, becoming 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, but
may be locally stronger downwind of coastal gaps.

Winds veer to the south on Wednesday as another frontal system
approaches the waters, then increase with gusts up to 30 kt
through Wednesday night, with the strongest gusts likely to
remain beyond 10 NM offshore. Behind the passing front, winds
become northwesterly and weaken through Thursday. A building
westerly swell moving into the waters will most likely see seas
become steep and hazardous by Thursday afternoon with wave
heights of 14-16 ft and a dominant wave period of 14-15 seconds.
While this is the most likely outcome, there remains notable
uncertainty: there is a 10% chance that waves only reach 10-13 ft,
and there is equally a 10% chance seas reach 18-19 ft by Thursday
afternoon. Seas are then expected to slowly subside to 10-13 ft
on Friday, then persisting through the weekend. -36/42

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

$$

www.weather.gov/portland

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