291
FXUS66 KPQR 050454 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
954 PM PDT Fri Sep 4 2026

Updated Aviation Discussion...

.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...Today through Thursday...This afternoon a
vertically stacked low pressure system continues to churn right
along the central Oregon coastline with showers and isolated
thunderstorms progressing largely south to north across western
Oregon and southwest Washington. As daytime heating peaks, the
latest HREF indicates MUCAPE values top out around 300-600 j/kg
however with effective shear values near 8-13 knots only weaker
pulse-like thunderstorms are anticipated. The strongest
convection may produce infrequent lightning, heavy rain, small
hail, and gusty outflow winds. Headed through the evening hours
activity weakens and decreases thanks to the loss of daytime
heating. Given the lighter winds, ample surface moisture, and
partial clearing overnight, patchy fog is likely across
portions of the region by sunrise Saturday.

This weekend, the majority of deterministic models and their
ensemble counterparts continue to show the broad upper-level low
pressure system holding over the Pacific Northwest with
multiple weak shortwaves embedded within the larger
circulation. Anticipated additional lingering 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 with similar impacts what we`ll see today
(Friday). 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.

Come Monday into early next week the majority of ensemble
members finally show the upper low ejecting eastward favoring
the return of dry conditions by the second half of Monday
through Tuesday coinciding with a gradual warming trend. After
Tuesday into Wednesday ensembles begin to deviate from one
another when trying to resolve the upper-level pattern,
particularly in regards to a ridge of high pressure trying to
develop over the Rockies into southeast Oregon while a trough
amplifies over the eastern Pacific. This latter trough feature
is also going to be influenced by the eventual northerly
progression of Hurricane Marie in the eastern Pacific. The
majority of ensemble favor a warmer/drier solution on Wednesday
with highs near to a touch above normal. It remains to be seen
when or if the leftover remnant moisture from Marie swings into
the Pacific northwest, but at least a decent subset of
ensembles (30-40%) show this as a potential solution around
Thursday/Friday of next week - something we`ll have to watch.
-99/03

&&

.AVIATION...Through 06Z Sunday...A low pressure system remains
in place over the region as of 04Z Sat, maintaining some moist and
variable flow aloft. Rain continues to dwindle heading towards
06Z Sat, with rain showers currently remaining over the Oregon
Cascades/foothills, and near KCVO. Expect rain showers to end by
06Z Sat throughout the airspace. Expect most terminals to maintain
VFR conditions through the TAF period, with the exception of KONP
where conditions may bounce between MVFR and VFR through the night
and become predominantly VFR by 18Z Sat. With wet ground and the
potential for clearing skies tonight for areas south of a line
from KTMK to KUAO, 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. These chances of fog are
also favored by overall light and variable surface winds
throughout most of the airspace. 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 Saturday afternoon,
although mostly focused over the Cascades and Coast Range. Any
storms that do develop will have the potential to produce
lightning, gusty/erratic winds, and small hail.


KPDX AND APPROACHES...VFR conditions persist through the TAF
period, with a 10-20% chance of MVFR CIGs between 13-17Z Sat.
Light winds expected through the TAF period. ~12

&&

.MARINE...Surface low pressure will continue to weaken as it sits
off the central OR coast through tonight. Easterly winds will
continue to ease today, becoming more northerly tonight across the
northern waters, with light and variable winds expected by
Saturday morning. Seas have fallen to around 6 ft at 10 seconds
and will continue to subside to around 4 to 5 ft by Friday
evening. Also, a 15% chance for thunderstorms exists across the
inner waters south of Cape Foulweather Friday afternoon, which
could produce lightning and gusty/erratic winds.

Northerly winds return later Saturday 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 5 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

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

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