856
FXUS66 KPQR 050908
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
208 AM PDT Sat Sep 5 2026

.SYNOPSIS...Expect a showery, unsettled airmass to remain
overhead into the weekend with cooler than normal temperatures
persisting. Conditions trend drier by the early to middle
portion of next week as high temperatures gradually rise back
closer to normal for early September. However, uncertainty in
the large scale pattern grows noticeably around the middle to
end of next week.

&&

.DISCUSSION...Saturday through Friday...The upper level low
pressure system remains situated over the PacNW this weekend as
the surface low has weakened over the coast. Very light winds
early Saturday morning through Sunday morning with clearing
upper level clouds will lead to the potential of low stratus or
fog development in the morning hours each day along the coast
and interior lowlands. Multiple weak shortwaves embedded
within the larger upper low pressure circulation will bring
additional shower chances over NW OR and SW WA, most likely
during the daytime hours and over terrain features as diurnal
heating likely plays a major role in shower generation. Also
can`t rule out stronger cells or a pulse-like thunderstorm or
two forming in the afternoon and evening hours each day. Brief
heavy rain, small hail, and gusty winds are possible with any
strong shower or thunderstorm that forms. Confidence remains
high that temperatures hold below normal for this time of year
with upper 60s to mid 70s in the interior lowlands, 60s along
the coast, and 40s to low 60s over the Cascades (coldest at
higher elevations). If you`re venturing up in the mountains to
enjoy the weekend it may be worth packing a jacket.

Ensemble guidance is in high agreement that the upper low will
finally move eastward Monday into Tuesday, into Idaho by late
Monday and southern Canada by Tuesday. This will bring dry
conditions by midday Monday and temperatures warming back to
near normal by Tuesday as most ensemble members indicate zonal
flow begins to take shape over the PacNW.

Wednesday into Thursday, ensembles begin to deviate from one
another over the PacNW as they try to resolve the upper-level
pattern, particularly in regards to a ridge of high pressure
over the central US trying to amplify northwest over the Rockies
into southeast Oregon while a trough amplifies over the eastern
Pacific. About 80% of ensemble members indicate at least zonal
flow if not slight ridging over the area on Wednesday, leading
to the warmest temperatures of the week with a 75-85% chance of
interior lowland temperatures exceeding 80 degrees and a 40-60%
chance for exceeding 85 degrees. By Thursday, about 50% of the
members hold on to this pattern with the other 50% indicating
weak to moderate troughing developing over the area. By Friday,
about 70-80% of the ensemble members suggest troughing impacting
the region, though precipitation chances with this are extremely
variable. This trough feature could be influenced by the
eventual northerly progression of remnants from Hurricane Marie
in the eastern Pacific with around 50-60% of ensemble members
suggesting this in the Thursday/Friday timeframe. However, how
much moisture lingers from Marie and how much this will impact
the PacNW is very uncertain at this point. Will be keeping an
eye on this as Marie progresses through the Pacific over the
next week. -03/99

&&

.AVIATION...Through 12Z Sunday...A low pressure system remains in
place over the region, maintaining some moist and variable flow
aloft. Predominately VFR conditions, with the exception of KONP
where conditions may bounce between IFR/MVFR/VFR through the night
and become predominantly VFR by 18Z Sat. With wet ground and the
potential for clearing skies tonight, and light and variable wind
for areas south of a line from KTMK to KUAO, low stratus or fog
development is possible. Guidance suggests a 40-60% chance of
MVFR, 20-40% chance of IFR, and 5-20% chance of LIFR conditions
between 12-18Z Sat for KONP, KSLE, and KEUG. Any lowered flight
levels should improve to VFR by 16-19z Sat. There`s a 50-60%
chance of marine stratus redeveloping at KONP by 06-10z Sun with a
20-50% chance of low stratus or fog in the southern Willamette
Valley after 09-12z Sun. The coast will see light southeasterly
winds shift northwesterly in the afternoon and strengthen but
remain under 8 kt.

A 15-25% chance of thunderstorms return between 18Z Sat through
03Z Sun, mostly focused over the Cascades and Coast Range. Any
storms that do develop will have the potential to produce
lightning, gusty/erratic winds, small hail, and heavy rain.

KPDX AND APPROACHES...VFR conditions could bounce between MVFR
through 17Z Sat, with a 20-30% chance of more persistent low
stratus or fog development producing MVFR/IFR conditions between
13-17Z Sat. Light and variable winds expected through the TAF
period. ~12/03

&&

.MARINE...Surface low pressure will continue to weaken into early
Saturday morning as it sits off the OR coast. Northerly winds that
developed across the waters overnight are becoming light and
variable this morning. Seas have fallen to around 4 to 5 ft at 10
seconds.

Northerly winds return later today into Sunday as weak high
pressure rebuilds over the waters. Winds are expected to peak at
around 15 kt or less. Seas remain at around 3 to 6 ft through the
weekend. Conditions look to remain rather benign into early next
week, though high pressure may strengthen toward the middle of
next week. -DH/03

&&

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

&&

$$

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