233
FXUS66 KPQR 151032
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
332 AM PDT Tue Sep 15 2026

.SYNOPSIS...A weak trough will bring increasing clouds and a
few light showers to the higher terrain today, with seasonably
cool temperatures continuing. Warmer and drier conditions return
Wednesday and Thursday as easterly flow develops, followed by
renewed uncertainty in temperatures Friday through the weekend.

.DISCUSSION...Now through Sunday...The weather pattern will
undergo a fairly noticeable transition over the next couple of
days. For today, a weak upper-level trough will move across the
Pacific Northwest while moisture remains limited. Increasing mid
and high level clouds overnight will likely be followed by
areas of low clouds and patchy fog in the interior valleys this
morning. Some cloud cover should persist into the afternoon,
keeping temperatures in the upper 60s to low 70s across the
interior and in the 60s along the coast. Despite the passage of
the trough, measurable precipitation is unlikely for most
locations. The best chances, around 30-50%, will be confined to
the North Oregon Coast Range, Willapa Hills and Cascade crest,
with probabilities around 5-15% elsewhere.

The trough will shift southward tonight into Wednesday as
ridging strengthens offshore and begins to build into the
Pacific Northwest. This will mark the start of a much warmer
pattern, with interior highs climbing into the upper 70s to low
80s Wednesday. A developing thermal trough along the coast and
Cascade foothills will also turn the low-level flow offshore,
resulting in increasing easterly winds through the Columbia
River Gorge and other east-west oriented terrain gaps. Pressure
gradients between KTTD and KDLS are expected to fall into the -1
to -3 mb range, supporting gusts around 20-25 mph in the Gorge
and locally breezier conditions over exposed terrain and
ridgetops. The central and southern Willamette Valley should
also become breezy as winds turn more northerly. There is a
30-50% chance of gusts exceeding 30 mph in the Gorge Wednesday,
with probabilities around 5-15% across the central and southern
Valley. Despite the warmer temperatures and increasing winds,
afternoon humidity should remain above 30%, keeping fire-weather
concerns minimal.

Thursday currently appears to be the warmest day of the week.
Weak offshore flow will continue through the morning, with
moderate to high confidence for interior temperatures reaching
the low 80s. The thermal trough should then weaken Thursday
afternoon, allowing onshore flow to return and limiting further
warming. Meanwhile, the upper-level trough will shift east
toward the Great Basin. Some wrap-around moisture could produce
a 5-10% chance of thunderstorms along the crest of the Lane
County Cascades Thursday, while the remainder of the forecast
area remains dry and outside the thunderstorm threat. SPC has
included a portion of the Lane County Cascades in a general
thunderstorm risk, so this potential will need to be monitored
as Thursday approaches.

The forecast becomes more uncertain Friday through the weekend
as ensemble guidance diverges on how quickly the upper-level
pattern evolves. Roughly half of the guidance maintains weak
troughing over the Great Basin, which would keep temperatures
closer to the low 70s, while the other half favors stronger
ridging over the Pacific Northwest and warmer temperatures
potentially reaching the mid 80s. Thus, there is still a fairly
broad range in possible temperatures late in the week, but the
overall signal continues to favor dry weather with above-
seasonal-average temperatures. ~12


&&

.AVIATION...Through 12Z Wednesday...Westerly flow aloft will
grdadually shift northerly as an upper level trough drops south
towards northern California. High clouds continue to drift
southeastward into the airspace, with ceilings above 20 kft
gradually lowering through the TAF period. Expect predominantly
VFR conditions through the TAF period, with the exception of a
30-50% chance of MVFR CIGs at coastal terminals before 20Z Tue
and a 20-30% chance of brief fog at KEUG before 17Z Tue.
Otherwise, expect light winds this morning to become north to
northwesterly around 5-8 kt through the afternoon, possibly up
to 10 kt at coastal terminals.

KPDX AND APPROACHES...VFR conditions are expected through the TAF
period, with high clouds overhead. Light winds this morning will
become northwesterly around 3-6 kt throughout the TAF period. ~12


&&

.MARINE...
North to northwest winds continue today as high pressure builds
offshore. A strengthening thermal trough along the coast is
expected to increase pressure gradients across the coastal
waters on Wednesday, increasing northerlies to 15-20 kt with at
least an 80-90% chance for wind gusts exceeding 21 kt south of
Cape Falcon. As a result, Small Craft Advisories have veen
issued for the waters south of Cape Falcon from 2 to 11 PM
Wednesday. Small Craft winds could hold on until 2 AM Thursday
but confidence remains low at this time. Winds are likely to
ease later in the week as low pressure drifts offshore. A
persistent northwest swell around 4 to 5 ft at 7 to 8 seconds is
expected to continue through Tuesday. Seas then build to around
6 ft on Wednesday as northerly winds strengthen. ~12/23


&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory from 2 PM to 11 PM PDT Wednesday for
     PZZ252-253-272-273.
&&

$$

www.weather.gov/portland

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