559
FXUS66 KPQR 190933
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
233 AM PDT Tue Aug 19 2025

.SYNOPSIS...Troughing over the northeastern Pacific Ocean will
give way to high pressure building northwest from the Desert SW
later this week. Persistent onshore flow will help to moderate
daytime high temperatures through the middle of the week.
However, the building high pressure late this week will produce
warmer temperatures with Moderate HeatRisk inland as well as
weak offshore flow.

&&

.DISCUSSION...Tuesday through Monday...Relatively benign weather
is expected Tuesday into Wednesday as upper level troughing over
the eastern Pacific continues onshore flow for NW Oregon and SW
Washington. This will keep daytime temperatures near daily
normals with low to mid 80s for inland valleys and 60s along the
coast.

A significant pattern change is in store for the region beginning
Thursday. Ensemble guidance indicates upper level high pressure
centered over the Desert SW begins spreading northwest,
allowing for a warming trend. Temperatures on Thursday are
forecast to peak in the upper 80s to low 90s for inland valleys.
Additionally on Thursday, a surface thermal trough is expected
to push north into Oregon. Depending on the location of the
thermal trough as well as how far north into the state it
develops, surface pressure gradients could tighten over the
Willamette Valley and the Columbia River Gorge, causing some
measure of increased offshore (north to east) winds. Latest NBM
guidance indicates a 40-60% chance of wind gusts exceeding 20
mph from 2-8 pm between Salem and Eugene but only a 5-20% chance
of reaching 25 mph. Additionally, there`s only a 5-20% chance of
sustained winds reaching 15 mph for the same time and locations.
With minimum relative humidities expected to fall below 25% with
the increasing temperatures, increased winds could cause
elevated fire weather concerns. However, there`s only a 30-40%
chance of meeting Red Flag Warning criteria at this time (wind
speeds of 15+ mph and/or wind gusts of 25+ mph coinciding with
relative humidities of 25% or less for 4 hours or more). It`s
still important to note that fire safety should be practiced on
Thursday.

Friday into Saturday, ensemble guidance is in very good
agreement that the high pressure will continue spreading
northwest into Oregon and southern Washington, causing
temperatures to warm even more. Latest NBM forecast indicates
high temperatures in the mid to upper 90s for inland valleys.
There`s a 70-90% chance of temperatures exceeding 95 degrees on
Friday and 40-70% chance on Saturday for the Willamette Valley,
Portland/Vancouver metro area, Columbia River Gorge, and Hood
River Valley. There`s also a 20-50% chance of temperatures
reaching 100 degrees on Friday, mainly from Corvallis to the
Portland/Vancouver metro area, which provides confidence that
Friday will be the hottest day. Ensemble guidance indicates
the high pressure begins slowly shifting east on Sunday, though
not as much as previous runs. Latest NBM guidance has increased
chances of temperatures remaining above 90 degrees (55-90%) and
for temperatures reaching 95 degrees (20-45%), with highest
probabilities south of the Portland/Vancouver metro area.
Additionally, overnight temperatures are expected to remain
above 60 degrees for inland locations around and north of Salem
and near to above 70 degrees for the Columbia River Gorge for
Friday night through Sunday night. This combination of warm
daytime temperatures and mild overnight temperatures is
producing widespread Moderate HeatRisk Friday through Sunday and
locally Major HeatRisk in the Columbia River Gorge. This means
those who are vulnerable to the heat are at risk for heat-
related illnesses, including those with outdoor plans and those
without access to adequate cooling.

By Monday, ensemble guidance suggests the high pressure will
continue shifting southeast, though there are subtle differences
on how much it will shift, which is causing more uncertainty in
the high temperature forecast. NBM indicates a 45-65% chance of
temperatures reaching or exceeding 90 degrees again across the
Willamette Valley but only a 15-35% chance of reaching 95
degrees. -HEC

&&

.AVIATION...Mainly VFR conditions are expected across the airspace
through the TAF period. Guidance suggests sub-VFR conditions
along the coast but current observations show clear skies and very
little cloud cover in the area. HREF guidance has also continued
to back off on stratus development along the coast with only a
20-30% chance for sub-VFR CIGs developing. Starting to see some
stratus develop around K6S2 so could see some stratus build
northward towards KONP but confidence is low. VFR conditions
persist inland with SCT to BKN clouds around FL050-FL060
dissipating by 12-14z. Light and variable winds overnight will
increase after 20z to between 4-7 kt from the N/NW.

PDX AND APPROACHES...There is high confidence for VFR conditions
through the TAF period. SCT to BKN clouds around FL050-FL060
persist through early Tuesday morning. Light winds overnight
increase to around 5 kt from the northwest after 21z. -Batz

&&

.MARINE...Benign conditions are expected to persist through
midweek with light southerly to southwesterly winds and seas of
4-6 ft driven largely by a subsiding west-northwesterly swell at
9-10 seconds. High pressure building over the northeastern Pacific
will see winds shift out of the northwest to north by Tuesday
night, with a 70-90% chance of gusts exceeding 20 kt on Wednesday
across most of the waters, highest within the inner waters. The
pressure gradient across the waters is expected to tighten on
Thursday and Friday, leading to increasing probabilities for
Small Craft Advisory conditions. Probabilities for wind gusts of
25 kt or greater have jumped to between 50-90% across the waters,
highest along the central coast of Oregon. -Batz

&&

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&

$$

www.weather.gov/portland

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