110
FXUS66 KPQR 042119
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
219 PM PDT Fri Sep 4 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...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 00Z Saturday...A low pressure system
remains over the region late this afternoon with moist,
southerly flow across the area. Most TAF sites remain VFR even
with the showers and cloud cover rotating around the region but
brief reductions to MVFR is possible at times with heavier
showers. Chances for thunderstorms (15-30%) will persist for the
next several hours this afternoon as well, ending by 02-04z. Any
storms that do develop will have the potential to produce
lightning, gusty/erratic winds, and small hail. Once showers
decrease overnight we`ll have to keep an eye on the amount of
clearing approaching the sunrise hours as the recent rainfall and
lighter winds will present the ingredients for patchy fog
formation. Currently KSLE and KEUG have the best chance for patchy
fog between 11-16z with a 15-20% chance for IFR or lower
conditions. Higher confidence in widespread VFR CIGs/VIS 17-18z
onward. Generally expect light and variable winds inland with
southeasterly winds less than 10 kt along the coast.

KPDX AND APPROACHES...This afternoon as of 21z a band of
showers and embedded T-storms are approaching the terminal from
the south, likely passing to the north by 22-23z. Expect
scattered showers into the evening with a additional chances for
isolated thunderstorm activity until sunset. While VFR conditions
are favored most hours, models do show a 15-20% chance for MVFR
conditions 12-16z Saturday. Light winds expected through the TAF
period. -99/DH

&&

.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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