853
FXUS66 KPQR 110515
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1015 PM PDT Thu Sep 10 2026

Updated aviation discussion.

&&

.SYNOPSIS...The overall weather pattern remains fairly
progressive heading into mid-September with temperatures
gradually cooling into the weekend. Saturday through the first
half of Sunday a low pressure system ushers in a period of
widespread rain shower activity and unsettled conditions.
However, we`ll quickly transition back into a sharp warming and
drying trend by the early to middle portion of next week.

&&

.SHORT TERM...Now through Sunday...This afternoon the region
remains under the influence of broad northwesterly flow as a
weak upper-level shortwave trough pushes into the Pacific
Northwest. There is an accompanying dry cold front just
beginning to work into northwest Oregon and southwest Washington
as well which will pass overhead this evening leading to cooler
temperatures come Friday morning - overall little in the way of
direct impacts. Due to clearing skies across the inland areas
come sunrise Friday behind this feature in addition to light
winds and decent surface moisture, patchy fog and/or low clouds
are anticipated across the inland valleys. The next upper level
low will begin approaching the region as Friday progresses
bringing additional cloud cover while keeping temperatures
suppressed during the afternoon. High temperatures likely fall
into the upper 60s to low 70 degree range for the interior
lowlands and low to mid 60s for the coast, around 5-10 degrees
below normal for this time of year. For those who enjoy more
summer-like temperatures we`ll likely swing back that direction
by the middle of next week - more on that in the long term
discussion.

Ensemble guidance from the GEFS/GEPS/ENS indicates the
aforementioned upper level low pressure system deepens just off
the coast late Friday into early Saturday morning before
shifting east and moving inland by Saturday afternoon. This
weather system will facilitate our next round of widespread
rain showers for Pacific Northwest, though some uncertainty
still remains in the exact timing of precipitation as the latest
model guidance has trended a touch slower than previous runs.
Rain is forecast to begin sometime Saturday morning along the
coast and spread inland sometime between midday Saturday and
late Saturday afternoon. With the slowing of the precipitation
onset, rain is now expected to continue into Saturday night with
showers continuing through Sunday for portions of the interior
lowlands and Cascades (best chance higher terrain features).
This could also impact thunderstorm chances on Saturday. If the
core of the low pressure system helping to destabilize the
atmosphere doesn`t move over the area until later on Saturday
when peak heating begins to wane, there is less chance for
deeper convection to develop, limiting thunderstorm chances.
However, cold core funnel clouds could still develop given the
overall pattern. Rotation with cold core funnel clouds rarely
reaches the ground or causes impacts, but it is not impossible.
They are also non-mesocyclonic in nature and can form without
strong deep-layer wind shear in place. Despite the model timing
differences, around 95% of model ensemble guidance suggests
measurable rain will occur with this system. The latest forecast
indicates total rain amounts ranging between 0.1-0.5 inch for
most locations, highest in the Cascades in Coast Range, although
amounts have increased across the southwest Washington
Cascades, closer to 0.5-1.0 inch there.

Thanks to this weather system temperatures cool even more on
Saturday and now likely stay very similar on Sunday due to
continued cloud cover and shower chances. The total NBM spread
for temperatures ranges is fairly low for both Saturday/Sunday,
with highs most likely between the upper 50s and mid to upper
60s for the interior lowlands. -99/03

.LONG TERM...Monday through Wednesday...Headed into the middle
of next week conditions trend noticeably warmer as ensemble
models begin to converge regarding the upper-level pattern. The
vast majority (>90%) of ensemble guidance depicts the upper
level low overhead ejecting eastward into the the Rockies and
Northern Plains by Monday. A weaker secondary upper-level trough
on the backside of this low looks to remain over Oregon and
Washington through at least Tuesday albeit degrading day to day
while a ridge of high pressure attempts to amplify over the
eastern Pacific. This will allow temperatures to rebound,
likely rising up into the mid 70s to low 80s across the inland
valleys by Tuesday afternoon. Come Wednesday the ensemble space
is now favoring (70-75% chance) the ridge of high pressure over
the eastern Pacific nudging closer towards the region pushing
temperatures even higher into the mid 80s across the lowlands -
only 25-30% of ensembles leave weak troughing overhead by this
point (thus lower temperatures than forecast). Given the
average placement of the ridge, offshore easterly flow is also
appearing more likely in the midweek timeframe as well -
something to watch. -99/03

&&

.AVIATION...Through 06z Saturday...Largely VFR flying conditions
expected with increasing chances for MVFR cigs as low stratus
develops overnight. Higher confidence in persistent 60-80%
chances for MVFR cigs at coastal terminals after 08-10z Fri,
while the likelihood of MVFR cigs at inland terminals is
generally lower, 30-60%, highest along the Cascade foothills and
at Portland-area terminals after 12-14z Fri, and lower
elsewhere along the Willamette Valley. There are additionally
10-20% chances for restricted vis within fog/mist within
sheltered valleys. Low clouds will tend to mix out by 16-18z
Fri, yielding a return to widespread VFR conditions.

Light west to northwest winds will ease to 3 kt or less
overnight, before building to 5-10 kt along the coast and to
around 5 kt inland by midday Friday.

KPDX AND APPROACHES...VFR conditions favored through at least
12z Fri, before chances for MVFR cigs reach 50-60% in the
hours around sunrise Friday morning. High confidence in further
VFR conditions after low clouds mix out after 18-19z Fri.
Northwest winds ease to 2-3 kt overnight, then build to around 5
kt by midday Friday. -36

&&

.MARINE...High pressure will maintain northerly winds across
all waters through at least Friday. Breezy north winds with
gusts reaching 20-25 kt will continue through this evening.
Marginally steep seas of 6-8 ft at 9 seconds will also continue
to pose a hazard to small craft beyond 10 NM through tonight
before easing. Therefore, Small Craft Advisories remain in
effect through 8 PM PDT this evening across the inner water
(within 10 NM) and across the outer waters (beyond 10 NM)
through 8 AM PDT Friday.

Another weaker system is expected to approach the coastal waters
from the north late Friday into Saturday. This will result in a
southerly wind shift along with seas subsiding towards 4 to 6 ft
and gusts below 20 kts. A more active pattern is expected to
return next Tuesday. This system looks to bring northerly winds
back into the forecast with gusts approaching 20 kt. Seas are
also expected to build towards 5 to 7 ft. -42/03

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.

WA...None.

PZ...Small Craft Advisory until 8 AM PDT Friday for PZZ271>273.

&&

$$

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