027
FXUS66 KPQR 232125
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
225 PM PDT Sun Aug 23 2026

.SYNOPSIS...Upper level ridging and low-level offshore flow develops
Monday, continuing into Tuesday, bringing warmer and sunnier
conditions with high temperatures in the mid 80s to lower 90s across
the interior lowlands, warmest on Monday. Wildfire smoke will also
begin to increase over the Columbia River Gorge, Upper Hood River
Valley, and the greater Portland/Vancouver metro area Monday morning
and then linger through Tuesday; however smoke is not expected to be
dense for most locations. Onshore flow arrives by Wednesday and
continues thereafter, which will clear any lingering smoke out of
the area and bring relatively cooler temperatures through the end of
the week and into the weekend.

&&

.DISCUSSION...Tonight through Saturday Night...Water vapor satellite
imagery reveals the upper level shortwave trough lifting across NE
Washington into Canada this afternoon. Heights aloft will continue
to increase through tonight allowing for clearing skies. As a ridge
of high pressure builds aloft over the region, a surface thermal
trough develops along the coast extending into western WA early
Monday morning. This will allow for light offshore flow to develops,
especially over the western slopes of the Cascades with east winds
increasing through the Columbia River Gorge later Monday morning.
Winds are not expected to be very strong, but gusts up to 25-30 mph
will certainly be possible through the western gorge. Temperatures
at 850 mb are also expected to rapidly rise to around 20C by Monday
evening. Downsloping winds and afternoon mixing will therefore allow
for surface temperatures to warm into the upper 80s to lower 90s
across much of the inland lowlands, as well as through Cascade
valleys, while temperatures at the coast will likely warm into the
70s before winds shift as sea-breezes occur early in the afternoon.
This offshore flow will also cause wildfire smoke to begin to filter
back down into the valleys, including into the Portland/Vancouver
Metro area, Columbia River Gorge and Upper Hood River Valley.
However, smoke is not expected to be dense for most locations.

By Monday evening, the surface thermal trough is expected to shift
east into the Willamette Valley, and potentially to the Cascade
crest, allowing for onshore flow to return across much of the area.
Lingering low pressure in the valley will likely allow for very
light offshore flow to return over the Cascade foothills Monday
night into early Tuesday. This will likely maintain elevated
overnight temperatures in the lower to mid-60s where the easterly
winds persist. A moderate risk of heat related illnesses will
therefore exist Monday into Tuesday. Wildfire smoke is also likely
to linger into Tuesday as well for northern portions of the forecast
area.

Early Tuesday, a shortwave trough will lift just offshore, skirting
the coast, as a deeper upper level low in the Gulf of Alaska drops
south. This should cause a southerly wind reversal to occur along
the Oregon coast and into the Willamette Valley. Heights aloft still
remain high with the axis of the upper level ridge over the
Intermountain West, but 850 mb temps cool to around 16-17C. Still
expecting Tuesday temperatures to warm into the mid to upper 80s
(about 4-8 degrees above normal). By Tuesday evening, surface high
pressure building along the coast will bring a strong marine push of
westerly winds. Any lingering wildfire smoke should shift back east
of the Cascades by Wednesday.

Models and their ensembles are showing fairly good agreement that
the upper level trough over the NE Pacific gradually pushes east
over the Pacific NW Wednesday through Thursday, with troughing
likely persisting over the region through the end of the week and
into the weekend. There is high confidence that temperatures trend
cooler to near or slightly below average. Confidence is low
regarding precipitation, if any will occur later this week. But, if
any rain does fall, it would most likely be very light. Best chances
would be drizzle along the coast with a weak frontal passage
Thursday morning; and again on Saturday, but PoP remains around 15%
or less.  /DH

&&

.AVIATION...00Z TAFs...Widespread VFR conditions with mostly clear
skies will likely prevail from 00Z Monday through 00Z Tuesday,
with one potential exception at the coast. By 11Z Monday, KONP has
a 50-60% chance for the return of low stratus with ceilings below
1000 ft and surface visibilities around 2 SM or lower.
Probabilities for low stratus to return to KAST are lower at
around 20%. Inland TAF sites have around a 10-20% chance to see a
brief period of MVFR low stratus between 12-17Z Monday. Aside from
KONP, these probabilities are not high enough to justify a
mention in the TAFs.

Expect breezy northerly winds along the coast through 03Z Monday,
gusting upwards of 20 kt at KONP. Winds will be relatively weaker
inland, mainly out of the north to northwest. Around 18-20Z
Monday, easterly winds around 8-11 kt are expected to develop at
KTTD and KPDX as offshore winds develop through the Columbia River
Gorge. This will also push some wildfire smoke into the Gorge and
greater Portland/Vancouver metro area Monday morning. Although
dense smoke is not expected, slantwise visibilities may be
reduced. In addition, temperatures are expected to warm into the
lower 90s Monday afternoon at the inland TAF sites, so be aware of
high density altitude which may reduce aircraft performance.

KPDX AND APPROACHES...Expect VFR flight conditions with mostly
clear skies from 00Z Monday through 00Z Tuesday. Light winds
should become northwest around 7-8 kt by 00Z Monday with an
incoming sea breeze. Winds become light again by 08Z Monday,
before becoming easterly around 8-11 kt sometime between 18-20Z
Monday. Once the easterly winds begin, expect increasing wildfire
smoke at and near the terminal. Although dense smoke is not
expected, slantwise visibilities may be reduced. Temperatures are
expected to warm into the lower 90s Monday afternoon at the
terminal, so be aware of high density altitude which may reduce
aircraft performance. -23

&&

.MARINE...Northerly winds will gradually increase Sunday afternoon
and evening as high pressure strengthens over the northeast
Pacific. Gusty winds will develop over the waters, increasing from
south to north from Florence to Cape Shoalwater. Wind gusts up to
25 kt are expected to develop Sunday evening over the southern
and central waters, and over the northern waters Sunday night.
These wind speeds will then persist through Monday afternoon/early
evening before decreasing Monday night. Small Craft Advisories
remain in effect from 5 PM Sunday to 5 PM Monday for the coastal
waters from Florence north to Cape Falcon and from 11 PM Sunday to
8 PM Monday for the coastal waters north of Cape Falcon to Cape
Shoalwater. Gusty north winds up to 25 kt are also expected for
the Columbia River Bar starting at 8 AM Monday, which also has a
Small Craft Advisory in effect.

A southerly wind reversal arrives early Tuesday morning over the
inner waters with gusts up to 15-20 kt expected by Tuesday
afternoon. This will also bring increasing chances for marine fog
beginning early Tuesday morning, especially over the inner
waters. Visibilities may fall below 1 SM at times as the southerly
winds develop and upwelling occurs. Aside from the increasing
winds and potential marine fog, significant wave heights look to
remain relatively low at around 3 to 5 ft through Friday. -23

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 8 AM to 8 PM PDT Monday for PZZ210.

     Small Craft Advisory from 11 PM this evening to 8 PM PDT Monday
     for PZZ251-271.

     Small Craft Advisory from 5 PM this afternoon to 5 PM PDT Monday
     for PZZ252-253-272-273.
&&

$$

www.weather.gov/portland

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