715
FXUS66 KPQR 140338 AAA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
838 PM PDT Wed Aug 13 2025

Updated Aviation Discussion

.SYNOPSIS...
Cooler conditions have arrived today as the strong high pressure
ridge weakens and onshore flow increases. Inland highs will
trend closer to seasonal norms, while marine clouds and patchy
coastal fog linger along the shoreline. A strong trough will
move in from the Gulf of Alaska late Thursday into Friday,
bringing widespread rain, breezy conditions, and a more
pronounced drop in temperatures. Drier and gradually warmer
weather is expected to return early next week.

&&

.SHORT TERM...Now through Thursday Night...The midweek cooldown
is underway, with inland temperatures running roughly 10-15
degrees lower than Tuesdays highs. Skies remain mostly sunny
across interior valleys, as todays onshore flow has not been
strong enough to push marine stratus into the Willamette Valley.
Coastal areas are seeing a mix of lingering low clouds and some
breaks of sunshine this afternoon, following pockets of dense
fog earlier in the day - mainly south of Lincoln City.

This evening, conditions will stay mild, with overnight lows
dipping into the upper 50s to low 60s for most inland location.
Along the coast, low clouds and fog will redevelop overnight
into Thursday morning, potentially reducing visibility before
lifting later in the day.

On Thursday, the first trough moves east while a stronger system
approaches from the Gulf of Alaska. This will maintain and even
strengthen westerly onshore flow, reinforcing cooler air and
bringing more marine influence. Highs will be near or slightly
below seasonal averages - upper 70s to low 80s inland, and 60s
along the coast. Most areas will remain dry through the day, but
rain chances will increase during the evening particularly
along the north Oregon and south Washington coasts. Coastal
rainfall totals by late Thursday night could reach 0.10 to 0.25
inches, with the highest amounts north of Astoria.

.LONG TERM...Friday through Tuesday...A stronger Pacific system
will arrive Friday, ushering in widespread rain and cooler-
than-normal temperatures across the region. The associated warm
front will bring steady precipitation during the day, followed
by a cold front Friday night into early Saturday. Rain will be
accompanied by breezy southerly to southwesterly winds,
especially along the coast and high terrain.

While confidence is high that most areas will see measurable
rainfall, amounts will vary depending on the exact track of the
system. Current trends suggest the heaviest totals north of
Salem, with lighter - but still significant - amounts to the
south. There is around a 40-70% chance for Friday 24 hour total
rainfall to exceed 1 inch at the coast (north of Lincoln City),
Cascades (north of Government Camp), and north of Portland. A
30-50% chance for Friday 24 hour total rainfall to exceed 0.5
inch for all other areas south of the aforementioned locations.
Saturday, precipitation will move more inland, giving a 40-60%
chance for Saturday 24 hour total rainfall to exceed 1 inch in
the Cascades. Otherwise, highs on Friday and Saturday will
generally stay in the mid to upper 70s inland.

The pattern will be generally unfavorable for thunderstorms,
though a brief window of instability could develop Saturday
afternoon behind the cold front, mainly along the Cascades.
Specifically, there is a 15-20% chance for thunderstorms in the
Cascades and a 5-10% in the valley.

From Sunday through early next week, the trough will weaken and
shift eastward, allowing for drier weather and a gradually
warming trend. However, residual onshore flow will likely keep
temperatures near or just below normal through at least Monday.
~Hall

&&

.AVIATION...Westerly flow aloft persists as upper level trough
moves over the region. Moisture remains confined to the lower
levels tonight through Thursday morning, with marine stratus
expected to persist along the coast. IFR to LIFR conditions likely
at KONP with around a 60% chance of fog reducing vsbys to 1/2SM.
Low clouds also likely to develop near the western slopes of the
Cascades and backbuild toward the I-5 corridor overnight. Chances
for MVFR CIGs have increased through the Willamette Valley, with
highest chances (60-80%) at KEUG between 08-16z Thursday.
Elsewhere inland, chances for MVFR CIGs sit at around 40-60%.
Expect conditions to improve to predominately VFR and CIGs lifting
above FL050 by Thu afternoon as more midlevel moisture arrives.
Light rain is expected to approach the coast by 00z Friday.

PDX AND APPROACHES...Predominately VFR expected through the
forecast period. Expect increasing low clouds after 08z Thu, with
around a 50-60% chance of MVFR CIGs between 12-16z Thu morning.
Northwest winds 7-9 kt this evening expected to become light early
Thu morning. /DH

&&

.MARINE...Weakening high pressure will maintain northwesterly
winds across the waters through tonight with gusts around 10-15 kt
or less. Seas around 6-8 ft at 8-9 seconds today will gradually
fall to 5-6 ft at 7-8 seconds tonight.

Thursday begins a pattern change as a low pressure system in the
northeast Pacific shifts southeastward and turns winds more
southwesterly. Latest model guidance projects a high confidence
forecast in amplifying conditions during the frontal passage on
Friday. Winds will be the main threat on early Friday morning
through Saturday morning with a bulk of that front with a weak
coastal jet forming. Winds will be strongest in PZZ251 and the
northern most areas of PZZ252. Here, could see gusts as high as 30
kt. There currently a 20% chance of gale force winds near the
Columbia River Bar and northward, though confidence is low. During
this time, seas will be dominated by the wind wave.

Conditions will settle into Saturday as the bulk of the front
pushes inland and we become post frontal. Winds will become
northwesterly once again. -Muessle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

$$

www.weather.gov/portland

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