Lake Oswego, Oregon 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

509
FXUS66 KPQR 132210
AFDPQR

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

.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...Satellite shows the incoming low pressure center
spinning in the northeast Pacific which is pushing marine stratus
inland along the Coast. High pressure remains elsewhere keeping
skies VFR. Along coastal terminals, conditions are a bit more
variable bouncing between IFR and MVFR in an unpredictable manner.
Through the next 12 hours or so, the low pressure system will
drop down with a cold front moving inland. Will see a steady
decline of conditions. CIGs will remain VFR, but barely. Along the
Cascades, there is around a 30-50% chance of fog and/or low
stratus forming in the early morning on Thursday. Not expecting
fog to move into main Willamette Valley terminals, though there is
around a 40% chance of MVFR CIGs from KCVO eastward in the
valleys.

Within the Columbia River Gorge, winds are increasing with gusts
as high as 25 kt.

For those long-term planning, looking at a significant amount of
rain starting on Friday with breezy winds.


PDX AND APPROACHES...VFR through much of the forecast. Wind
direction has been a bit shifty today, though in general mostly
northwesterly less than 10 kt. Through the remainder of the
afternoon, diurnal heating will aid in increasing those
northwesterly winds. Overnight there is around a 30% chance of
MVFR CIGs forming after 10Z Thursday, with the highest probability
between 15-19Z Thursday. Low confidence in the ceiling forecast.

&&

.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...Small Craft Advisory until 2 PM PDT this afternoon for
     PZZ271>273.
&&

$$

www.weather.gov/portland

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