001
FXUS66 KPQR 300507
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1007 PM PDT Sat Aug 29 2026

Updated aviation discussion.

.SYNOPSIS...Weak low pressure will result in lingering showers
across southwest Washington and far northwest Oregon this
afternoon. Tomorrow through Monday, high pressure will return
dry and warm conditions with mostly sunny skies. Tuesday through
the end of the week, will see a significant pattern change
with cooler temperatures, widespread rain chances, and a 10-20%
chance for thunderstorms. Wednesday and Thursday are expected to
be the wettest days.

&&

.SHORT TERM...Today through Monday night...Radar imagery as of
early Saturday afternoon depicts lingering light showers across
southwest Washington and far northwest Oregon as an upper-level
trough gradually exits the Pacific Northwest. Later this
evening, expect conditions to dry out as high pressure rebuilds.
Will see ridging set-up over the region Sunday to Monday,
returning predominately warm and dry conditions with mostly
sunny skies. Temperatures tomorrow are expected to warm up
slightly with highs in the mid to upper 70s across interior
valleys with 60s along the coast. Monday will be the warmest day
of the week as the ridge reaches its peak amplitude and
supports afternoon highs in the low to mid 80s across interior
valleys.      -10

&&

.LONG TERM...Tuesday through Friday...A significant pattern
change begins on Tuesday as we head toward more fall-like
weather. The long term forecast is characterized by two separate
upper-level troughs, the first one approaching on Tuesday. This
initial trough will swing down from the Gulf of Alaska and track
towards southern Oregon and northern California. This will
result in increased cloud cover, cooler temperatures, and about
a 25-50% chance for light showers on Tuesday. Given the position
of this trough, will also see southerly flow aloft setting up over
our area. Southerly flow aloft is typically a favorable pattern
for thunderstorms as it brings more moist, unstable air from
the south. However, there is uncertainty with exactly how much
instability we would get from this trough, as model soundings on
Tuesday aren`t showing too much of an unstable layer in the
mid-levels of the atmosphere. For now, there is about a 10-15%
chance for thunderstorms across the region on Tuesday.

Wednesday to early Thursday morning will be the more significant
soaker days as the majority of ensemble members are showing a
second, much deeper upper-level trough dropping down into the
Pacific Northwest. The associated surface front swings through
on Wednesday, returning widespread rain, cooler temperatures,
and breezy winds from the south. Chances for exceeding 1 inch
of rain in 48 hours between 5 AM Wednesday to 5 AM Friday are
around 60-80% across northwest Oregon and southwest Washington,
with the highest chances along the coast, Coast Range, and
Cascades. Chances for exceeding 2 inches during this same
timeframe are around 25-45% for these higher terrain features,
and 10-20% along the I-5 corridor.

Thursday afternoon to Friday, the upper-level trough moves
directly overhead and we transition into a post-frontal
environment with lingering showers. Given that there will be
cooler air aloft, this will favor increasing atmospheric
instability and thus chances for thunderstorms. There is around
a 15-20% chance for thunderstorms on Thursday following the
initial frontal passage. Any passing thunderstorms may produce
lightning, heavy rain, erratic winds, and small hail. Overall,
while the upcoming rain will not quite yet be a "fire season
ender," it will definitely slow down fire season and help put a
damper on ongoing wildfires.       -10

&&

.AVIATION...Through 06z Monday...As of 05z Sunday, predominately
VFR conditions being observed across NW OR and SW WA. Marine stratus
will likely form again for the N OR and SW WA coasts after 06-09z
Sun, yielding SCT to BKN low clouds. There`s only a moderate chance
of MVFR cigs along the coast north of KTMK, around 40-60% chance at
any given hour, with a 30-40% chance south of KTMK. Will also likely
see SCT to BKN lower clouds reform inland after 10-12z Sun, with a
40-60% chance of MVFR ceilings for Portland area and SW WA
terminals, 20-30% chance elsewhere. Any lowered flight conditions
are expected to improve to VFR by 16-18z Sun. Winds generally north
to northeast less than 6 kts into Sunday morning, becoming north to
northwest and increasing to 8-12 kts after 18-21z Sun.

KPDX AND APPROACHES...VFR conditions prevail with a 40-60% chance of
MVFR cigs developing after 10-12z Sun. Cigs expected to improve to
VFR again by 16-18z. Winds generally north to northwest 3-5 kts,
increasing to around 8-10 kts after 22z Sun. -03

&&

.MARINE...An upper-level low moving inland along the Canada-US
border will be replaced by brief upper-level ridging Sunday
through Tuesday. North to northwest winds will strengthen as the
ridge builds, reaching diurnal peaks of 10-15 kt each of Sunday
and Monday afternoons. By Tuesday, more robust upper-level
troughing digging over the northeast Pacific will see winds shift
out of the south to southwest Tuesday morning. Largely wind-driven
seas through this period will persist at 3-5 ft.

As the aforementioned trough and associated surface frontal
features approach the coast Tuesday into Wednesday, southerly
winds will rise to 20-30 kt, with modest chances (around 50%) for
gale- force gusts, particularly on Wednesday. Seas will similarly
build above 10 ft as winds increase. Both winds and seas are then
expected to ease through the end of the workweek, however
uncertainty during this period remains high.        -36

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

www.weather.gov/portland

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