813
FXUS66 KPQR 061802 AAB
AFDPQR

Area Forecast Discussion...UPDATE
National Weather Service Portland OR
1102 AM PDT Sun Sep 6 2026

Updated Aviation discussion

.SYNOPSIS...Cooler than average temperatures continue today
with chances with showers and isolated thunderstorms as a
closed upper level low remains in place over the region.
Trending drier Monday through Wednesday with temperatures
gradually warming each day as low-level offshore flow develops.
The forecast becomes more uncertain Thursday into Saturday,
with the potential for weather conditions to range anywhere from
cool and showery to warm and dry depending on the evolution of
the large scale weather pattern.

&&

.DISCUSSION...Sunday through Saturday...Ensemble guidance is in
good agreement that today will be the last day the persistent
upper low pressure system churns over the PacNW before it
finally moves east of the Cascades tonight into eastern Oregon,
eastern Washington, and western Idaho. This low will bring
continued chances for showers and isolated thunderstorms
today across most of northwestern Oregon and southwestern
Washington before chances decrease from west to east this
evening as the low progresses eastward. Rain amounts will be
noticeably higher for many inland valley locations when compared
to Saturday. Although mainly dry conditions are favored at the
coast, relatively wetter conditions are expected inland over the
Willamette Valley, greater Portland/Vancouver metro area,
Columbia River Gorge, Cascades/foothills, and Upper Hood River
Valley. These areas have a 15-35% chance for 0.25 inches of
rain or more through 11pm PDT Sunday, except 45-60% in the
Cascade foothills and 55-85% in the Cascades. The additional
rain will continue to dampen fire season and keep wildfire smoke
out of the area. With the excess cloud cover and occasional
rain on Sunday, temperatures will remain cooler than average for
early September with highs mainly in the mid 60s to lower 70s,
coolest at the coast and in the Cascade foothills.

Although the aforementioned low will be well to the east of the
Cascades on Monday, a shortwave trough rotating counter-clockwise
around the low is set to move over Washington and possibly far
northern Oregon. Model ensemble guidance suggests this feature will
most likely produce very little to no rain at all, and the NBM backs
this up with probabilities less than 5% for 0.01 inches or more
between 5am PDT Monday and 5am PDT Tuesday except for 10-15% for
the Willapa Hills.

Temperatures will trend noticeably warmer Tuesday into
Wednesday with high confidence for dry weather as low-level
offshore flow begins to develop. On Tuesday, afternoon
temperatures will warm into at least the mid to upper 70s,
except lower 70s at the coast. Come Wednesday, widespread highs
in the 80s are expected. Even the coast has a chance to reach 80
degrees or warmer on Wednesday if offshore winds last into the
afternoon hours (5 to 15% chance, except a 20-50% chance for
inland coastal communities such as Astoria and Tillamook).

Come Thursday into Saturday, uncertainty increases
substantially in regards to the large scale weather pattern and
whether or not we will remain warm and dry or transition back to
a cool and showery weather pattern. On Thursday, a cluster
analysis for 500 mb heights shows around 40% of the total
ensemble space from the GEFS/ENS/GEPS produces weak upper level
troughing over B.C., western WA and far northwest OR. The
remaining 60% of the total ensemble space depicts some degree of
ridging over the area. The current deterministic forecast
aligns with the latter outcome, suggesting the continuation of
dry weather with highs still in the 80s for inland valleys,
albeit several degrees cooler than Wednesday. For Friday into
Saturday, clusters come into better agreement for upper level
troughing (around 90% of the total ensemble space shows some
degree of troughing over or near the area). However, there are
significant differences in the exact amplitude, location, and
timing of this trough, which will impact precipitation chances
and temperatures. As such, the NBM 10th to 90th percentile
temperature spread is very large for each day, ranging from
70-90 degrees on Thursday and 65-85 degrees on Friday. Friday
and Saturday currently have a higher chance for conditions to
trend cooler and wetter compared to Thursday, which the latest
deterministic NBM represents with a 10-20% chance of showers
Friday night into Saturday. Anyone with outdoor plans late in
the week should monitor the forecast for updates over the next
several days. -23/03

&&

.AVIATION...Through 18Z Monday...A low pressure system overhead
will shift east of the Cascades after 00z Monday with increasing
northerly flow aloft today. Steady rain across the Willamette
Valley will gradually dissipate becoming more showery through this
afternoon. Areas within the heaviest rainfall are experiencing
reduced VIS and lowered CIGs to low MVFR and brief periods of IFR.
Expect conditions to generally improve to widespread VFR by 20-21z
today. Confidence is high that marine stratus will push onto the
coast by 02-03z with low MVFR to IFR CIGs likely. There are also
increasing chances for MVFR stratus to develop after 12-14z Monday
across inland terminals. Expect generally light and variable winds
at most terminals through tomorrow morning.

KPDX AND APPROACHES...Predominately VFR conditions expected
through at least 12z Monday. Light rain expected to become more
scattered this afternoon as showers gradually dissipate through
04z Monday. There is around a 40-50% chance for MVFR stratus to
develop between 12-18z Monday. Light and variable winds expected
through the period, except SW winds to around 6 kt possible this
afternoon. /DH

&&

.MARINE...Weak high pressure building offshore will produce light
northerly winds of less than 15 kt through Monday. Rather benign
conditions then continue through at least the middle of next week
with surface high pressure strengthening as the stagnant upper low
ejects eastward, favoring stronger north winds Tuesday into
Wednesday. There`s a 60-80% chance of north wind gusts exceeding
21 kts across the waters Tuesday afternoon into Wednesday
morning. Seas continue at 3-6 ft with a dominant northwest swell
at 8-10 seconds. -36/03

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

www.weather.gov/portland

Interact with us via social media:
www.facebook.com/NWSPortland
x.com/NWSPortland