353
FXUS66 KPQR 200555
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1055 PM PDT Sat Sep 19 2026

.UPDATED AVIATION DISCUSSION.

&&

.SYNOPSIS...Seasonably warm and dry weather this weekend will
trend toward more typical early fall weather through the
workweek as temperatures cool and a weather system approaches
from the Gulf of Alaska. Uncertainty in the position of this
system leads to low chances for rain beyond midweek.

&&

.SHORT TERM...Now through Tuesday Night...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. After peaking on Sunday, upper-level heights
and mid-level temperatures will begin to trend downward on
Monday, leading to a general cooling trend across the region. At
the surface, temperatures will reach some 5-10 degrees above
normal inland Sunday afternoon, namely the upper 70s to low 80s,
while the coast remains near normal in the 60s. As onshore flow
strengthens Monday through Wednesday, inland temperatures will
steadily cool be a few degrees each day. Otherwise, longer
nights and light winds will favor periods of early morning fog
in sheltered valleys, and a typical fall pattern of low clouds
pushing inland overnight and clearing through the day.


.LONG TERM...Wednesday through Saturday...Model consensus
decreases beyond the middle of the week as uncertainty in the
position of an upper-level trough dropping southward from the
Gulf of Alaska increases. This uncertainty is reflected in the
increased spread in possible high temperatures as well as low
chances of rain from late Wednesday through Friday, but in
general, a trough located closer to the coast will favor rain
and cooler temperatures while a more distant trough will instead
favor drier weather and near-normal temperatures.

Mean forecast highs fall to the upper 60s inland and low 60s
along the coast by Friday, some 5 degrees below normal. However
the 80% confidence interval (the difference between the 10th
and 90th percentiles of the forecast distribution) nearly
doubles in width from 2 degrees F on the coast and 4-6 degrees
F inland on Wednesday to 4 degrees F on the coast and 6-10
degrees F inland on Friday. In general, Rainfall chances will
also increase as the trough approaches. There is good agreement
in the location of an initial passing shortwave on Wednesday,
with rainfall chances of only 10-15% along the south Washington
and far north Oregon coasts with higher chances farther north
on the Olympic Peninsula. Thursday into Friday, about one
quarter of ensemble members favor the coolest and wettest
scenario, resulting in fairly widespread 15-25% chances for
rain to end the workweek.       -36

&&

.AVIATION...Through 06Z Monday...Late this evening satellite and
surface observations show generally VFR conditions across the
region outside of some low clouds/fog along portions of the Oregon
coast and coast range. This low cloud/fog layer likely expands up
the coastline as the night progresses with widespread degraded
CIGs/VIS by 12-14z Sunday. Expect gradual improvement to MVFR at
coastal terminals by the midday hours with decent chances for at
least some clearing during the mid to late afternoon.

For inland terminals VFR conditions generally prevail for a few
more hours, however, high resolution guidance is becoming more
bullish on areas of fog/low clouds across portions of the
Willamette Valley around and just after the sunrise hours
(12-17z). KEUG has the highest chance (80%) for IFR/LIFR
conditions come 12-14z while probabilities are lower elsewhere.
Outside of the south Willamette Valley, KSLE, KUAO, and KTTD are
other sites which could see some degraded conditions (40-50%
chance) between ~13-18z but confidence in the exact placement
of the fog was too low to add it as a prevailing condition at
this time. High confidence (90%) in widespread VFR conditions at
inland sites Sunday afternoon and evening. Winds stay fairly
light overall outside of the coast where increasing
northwesterly winds at sites like KONP likely gust up around
15-25 knots in the afternoon.

KPDX AND APPROACHES...VFR conditions prevail through late
tonight. That said, we`ll need to keep a close eye on sunrise
fog/low cloud formation (13-16z) with the latest guidance
suggesting it remains just to the east (near the base of the
foothills) and south of KPDX. Would place the probability for
IFR or lower conditions at some point Sunday morning at ~30-40%.
Otherwise, high confidence in VFR conditions 17-19z onward with
fairly light winds (less than 10 knots) through the TAF period.
-99

&&

.MARINE...High pressure over the waters will maintain northerly
winds through this weekend. Northerly winds strengthen this
afternoon and evening with gusts up to 15 kt, strongest over the
waters south of Cape Falcon. 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
between 7 to 8 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. -10/23

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&

$$

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