876
FXUS66 KPQR 121743
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1043 AM PDT Sat Sep 12 2026

Updated aviation discussion.

&&

.SYNOPSIS...A cool and unsettled weekend is underway as an
upper-level low moves across the Pacific Northwest. Rain will
spread inland today, with showers continuing through Sunday and
a 10-20% chance of thunderstorms this afternoon and evening.
Conditions then turn progressively warmer and drier early next
week as high pressure builds offshore. Increasing easterly flow
by Wednesday and Thursday could bring gusty winds to the Gorge,
Cascades and nearby foothills, while also contributing to warmer
and drier conditions.

&&

.DISCUSSION...Now through Friday...The weekend storm system is
moving closer to the region this morning, with rain expected to
reach the coast late this morning and spread inland through the
afternoon. Showers will continue tonight and into Sunday as the
upper low moves eastward. Confidence is high that most of the
forecast area will receive measurable precipitation, with
temperatures remaining well below seasonal average through the
weekend.

Most locations should see around 0.10-0.40 inch of rain through
Sunday, while higher totals are expected in the mountains. The
southwest Washington and north Oregon Cascades are favored for
0.50-1.00 inch, with the highest amounts likely in southwest
Washington. There is some potential for locally heavier rainfall
if a more concentrated band of showers develops on the north
and northeast side of the low. A southward shift in this band
would increase rainfall totals across the Portland Metro,
particularly Saturday night into Sunday morning. At the higher
end of the forecast envelope, which is around a 10% chance at
this point, rainfall could reach 0.50-0.75 inch in the interior
lowlands and 1-2 inches in the Cascades, with the highest
amounts again favored in southwest Washington.

As the upper low moves east of the Cascades Sunday, showers
should become more scattered and increasingly focused over the
higher terrain. The inland valleys and immediate coast should
trend mostly dry by late Sunday afternoon, while the Cascades
could continue to see showers into the evening.

A 10-20% chance of thunderstorms exists from mid-afternoon
through this evening. The main limiting factor is timing, as the
period of strongest daytime heating only briefly overlaps with
the coldest air aloft. Even so, model soundings show enough
instability to support a few thunderstorms. Any storms that
develop could produce occasional lightning, brief heavy rain and
locally erratic wind gusts. Cold-core funnel clouds are also
possible with the stronger showers. These are typically short-
lived and remain above the ground, though a funnel reaching the
surface cannot be ruled out.

Cool conditions continue Sunday as clouds and showers linger
across the region. Interior highs should generally remain in the
upper 50s to mid 60s, with cooler readings possible in areas
that see heavier showers. The pattern then begins to change
Monday as the upper low moves farther east and high pressure
starts building over the eastern Pacific. A weak trough may
linger near the region into Tuesday, but temperatures should
steadily recover, reaching the low to mid 70s across the
interior valleys by Tuesday.

The warm-up becomes more pronounced Wednesday and Thursday.
Ensemble guidance now gives about a 75% chance that the
offshore ridge shifts closer to the Pacific Northwest,
supporting temperatures well into the 80s across the interior
lowlands. The remaining guidance keeps some troughing near the
region and would favor somewhat cooler temperatures.

Easterly flow is also becoming increasingly likely by midweek
as the ridge strengthens and lower pressure develops over
northern California. The strongest winds currently appear most
likely Wednesday into Thursday morning, with gusts of 25-35 mph
and isolated gusts near 40 mph possible in wind-prone areas of
the Columbia River Gorge, Cascades and adjacent foothills. The
tops of the Coast Range could also become windy, although
confidence is lower there. At the higher end of the forecast
envelope, around a 10% chance, gusts could reach 30-40 mph with
isolated gusts of 45 mph in the most exposed locations. The
combination of warmer temperatures, lower humidity and
increasing east winds Tuesday through Thursday could increase
fire-weather concerns. Increasing winds may also pose a risk for
downed trees and branches, particularly where soils remain
saturated. This period will be worth monitoring as we get
closer. ~12

&&

.AVIATION...Through 18z Sunday...VFR conditions prevail across
the airspace ahead of an approaching low pressure system. Cigs
will trend downward as rain arrives from the west from 22z
Sat-01z Sun, most likely bottoming out at low-end VFR levels of
3-5 kft inland and MVFR levels at coastal terminals this
afternoon to evening. Chances for MVFR cigs generally increase
through 06z Sun, reaching 70-80% at the coast and near 50% along
the I-5 corridor. 15-20% chances of isolated thunderstorms will
persist through the same period, with low probability terminal
impacts of gusty or erratic winds and heavy rain rates likely to
be brief if they do occur.

South to southwesterly winds will rise to 8-12 kt with gusts up
to 20 kt at coastal terminals and to 5-10 kt inland through
this afternoon, before easing to around 5 kt out of the south
tonight.

KPDX AND APPROACHES...VFR conditions favored through the period,
with increasing chances for MVFR cigs as rain shower begin
shortly after 00z Sun, reaching near 50% from 06z Sun through
tonight. 15% chance for an isolated thunderstorm this afternoon
and evening, with low confidence in the occurrence of brief
terminals impacts. South to southwesterly winds of 4-8 kt
through the period. -36

&&

.MARINE...An area of weak low pressure near Vancouver Island
strengthens slightly as it drops south over the waters today.
Winds have begun to shift out of the south and will increase to
around 10-15 kt with gusts up to 20 kt through the morning into
the afternoon. Heavier showers or thunderstorms that develop
with this low pressure system over the waters today could
produce stronger wind gusts and lightning. Sunday, onshore
southwesterly winds will persist as the low pushes inland. High
pressure rebuilds over the waters by Monday, returning northerly
winds to the coastal waters early next week. Lastly, seas are
expected to subside slightly to around 4-5 ft during the weekend
as a northwest swell persists at 9-10 seconds. ~12/DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

www.weather.gov/portland

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