932
FXUS66 KPQR 201142 AAA
AFDPQR

Area Forecast Discussion...UPDATE
National Weather Service Portland OR
441 AM PDT Sun Sep 20 2026

Updated aviation discussion.

.SYNOPSIS...Areas of fog and low clouds Sunday morning will give way
to sunny and warm conditions in the afternoon. Temperatures trend
cooler Monday through Friday as upper level troughing develops over
the Gulf of Alaska. Chances for rain have increased Thursday night
into Friday to 40-60% as troughing attempts pushing into western
Washington and western Oregon.

&&

.SHORT TERM...Now through Wednesday...Guidance is in strong agreement
that a broad but low-amplitude ridge will steadily shift eastward
through the middle of next week while being replaced by an
upper-level trough digging southward over the Gulf of Alaska. Upper
level flow will become southwesterly over Washington and Oregon ahead
of the aforementioned trough, with no signs of any significant
moisture pushing inland. As such, the forecast remains dry through
Wednesday. After upper level heights peak on Sunday, mid-level
temperatures will begin to trend downward Monday through Wednesday,
which will bring a cooling trend across the region.

Surface temperatures will reach around 4-7 degrees above normal over
inland areas Sunday afternoon after areas of morning fog and low
clouds lift, with highs most likely in the upper 70s to low 80s over
the lowlands. Meanwhile, temperatures will remain near normal at the
coast in the 60s. As onshore flow strengthens Monday through
Wednesday and temperatures cool aloft, surface temperatures will
steadily cool be a few degrees each day over inland areas. Otherwise,
longer nights and light winds will favor periods of early morning fog
in sheltered valleys each day, with a typical fall pattern of low
clouds pushing inland overnight and clearing through the day. -23

.LONG TERM...Wednesday night through Saturday night...The forecast
remains dry and mild Wednesday night through Thursday afternoon as
dry southwest flow aloft persists. However, chances for rain Thursday
night into Friday have increased due to an uptick in the number of
ensemble members showing at least some QPF over the area with an
approaching upper level trough. Chances for precipitation falling
within a 24-hour period ending at 5 PM Friday have increased to
40-60%. Exact timing and rain amounts remain uncertain, and around
30-40% of ensemble guidance continues to show no rain at all over the
Willamette Valley. Therefore, confidence is only moderate and it is
too soon to tell if Friday will for sure be a wet day or not.
Regardless of the outcome, chances for rain decrease significantly
Friday night into Saturday to less than 15%, suggesting multiple days
with rain are unlikely.

It is also worth mentioning that chances for frost increase over the
Upper Hood River Valley Friday night and Saturday night when there is
a 30-50% chance for overnight lows around 37 degrees or colder,
mainly in the Parkdale area. Probabilities are around 10% in Odell
and 1-5% in Hood River. Those with sensitive outdoor vegetation in
this area should monitor the forecast over the coming days. -23

&&

.AVIATION...Through 12Z Monday...Areas of fog and low stratus
continue to expand across the area this morning with calm winds in
place. LIFR to IFR visibilities and/or ceilings are impacting all
TAF sites as of 1100-1130Z Sunday, except at KHIO which will
likely hold off on low cloud development until approximately 13Z
Sunday. Similar to what was observed yesterday, fog and low clouds
will lift sometime between 19-21Z Sunday and give way to mostly
clear skies and VFR conditions.

Winds will stay fairly light through the TAF period, aside from
KONP where northwest winds will increase this afternoon with gusts
up to approximately 20 kt.

KPDX AND APPROACHES...Expect low stratus with ceilings ranging
between 500-800 feet through this morning, beginning sometime
between 12-13Z Sunday. Similar to yesterday, skies should rapidly
clear out sometime between 19-20Z Sunday and bring a return to VFR
conditions. Calm winds this morning should become predominately
northwest around 3-6 kt this afternoon. -23

&&

.MARINE...High pressure over the waters will maintain northerly
winds through this weekend. Northerly winds peak in strength
Sunday afternoon and evening when there is a 50-90% chance for
maximum wind gusts of 21 kt or slightly stronger across the
waters, with the highest chances across the inner waters out to 10
NM offshore. Given wind gusts of this magnitude are not expected
to be frequent or widespread, Small Craft Advisories are not
anticipated at this time. Significant wave heights will remain
around 3 to 5 ft through the weekend, mainly driven by a
persistent northwesterly swell with a dominant wave period near 7
seconds.

Northerly winds are expected to linger Monday through Wednesday,
with wind gusts generally staying under 20 kt. A long period
west-northwesterly swell is set to arrive either Monday afternoon
or evening, pushing seas up by one to two feet. However, seas
will not be particularly steep as the dominant wave period with
this swell will be around 11-13 seconds. -23

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

www.weather.gov/portland

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