461
FXUS66 KPQR 222254
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
354 PM PDT Fri Aug 22 2025

.SYNOPSIS...It`s hot! A prolonged heatwave likely persists
through at least Tuesday due to a robust ridge of high pressure
holding over the region. Moderate to Major HeatRisk for all
inland locations through this period as a result, with high
temperatures of 96-104F for inland valleys - little relief
during the overnight hours, especially urban locations. At least
a slow cooling trend finally pushes high temperatures back into
the 80s around the Thursday/Friday timeframe. Cascades
thunderstorms are also a growing concern late Sunday onward,
however, confidence in exact placement and timing is only low to
moderate beyond the broad set-up.

&&

.SHORT TERM...Now through Sunday night...Abnormally hot
temperatures are the name of the game and most important aspect
of the weather forecast moving through the next several days as an
upper-level ridge of high pressure stays largely stationary
across western CONUS. High confidence (95%+) continues for
daytime max temperatures to peak in the upper 90s to the 100-104
range across inland valleys through the weekend. These hot
daytime temperatures are also being assisted by a near surface
thermal trough lingering near the coast range helping to induce
easterly flow across the Cascades which is the surface pattern
we typically need to reach triple digits. In addition, overnight
lows will be running rather warm with many locations struggling
to drop below the upper 60s or near 70F, resulting in a
Moderate to Major HeatRisk across all inland areas. It`s
entirely possible sites like KPDX, KHIO, KTTD, and KSLE, etc.
tie or set daily records for the warmest high temperature and
warmest low temperature the next days should the current
forecast hold, and it likely will. Hopefully this helps to
illustrate unusual and impactful nature of our ongoing late
August heat-wave. The combination of hot daytime temperatures
plus warm overnight lows make it very difficult to for buildings
without air conditioning to sufficiently cool, exacerbating
heat impacts in a long-duration heat event such as this one.
Those vulnerable to heat should be extra cautious.

Beyond the heat, the next feature we`re keeping our eye on is a
surge of monsoonal moisture from the desert southwest/California
moving into Oregon later on Sunday into need week. While much
of this instability is capped over western Oregon, enough local
terrain forcing and mid-level moisture could (10-20% chance) be
available over the Lane County Cascades for convective
initiation. At least high resolution guidance like the UW-WRF
and REFS seem to favor the crestline eastward into central
Oregon thanks to W-SW winds aloft steering activity out of our
area Sunday/Sunday night. These steering winds do shift straight
southerly on Monday which is a cause for concern. -Schuldt

.LONG TERM...Monday through Friday...While temperatures begin
to slowly nudge lower Monday and Tuesday, the heat-wave will
still be underway with moderate to high confidence in daytime
temperatures around the mid to upper 90s across the interior
valleys. NBM indicates a 60-75% chance of temperatures meeting
or exceeding 95 degrees both days, and a 30-50% chance of
temperatures reaching 100 degrees (highest probability south of
Portland to Salem, and on Monday). These daytime highs in
addition to the continuation of warm overnight temperatures
keeping Heatrisk in the major category prompted the extension
of the Extreme Heat Warning through Tuesday evening for the
inland Valleys, Columbia River Gorge, and Cascade foothills.
Wednesday has decent confidence in temperatures remaining above
90 degrees (70-85% chance) for the Willamette Valley including
Portland area, with only a 40-60% chance for the SW Washington
lowlands. Ensemble guidance indicates the strong high pressure
finally begins breaking down Thursday and Friday as troughing
develops in the eastern Pacific.

A mentioned in the short term discussion, monsoonal moisture
and Cascade thunderstorms continue to be a concern through
Wednesday. While the steering flow does turn southerly starting
on Monday, it appears rather weak, suggesting any storms that
do develop would move very slowly. Given the high PWAT values in
place (>1"), heavy rain would be possible with any thunderstorm
that develops. As of right now, confidence remains low
regarding the exact location and coverage of storms. It`s also
worth noting high level convective debris from any thunderstorms
may impact/decrease high temperatures, depending on the
coverage and timing. -Schuldt/HEC

&&

.AVIATION...Dry southwest flow aloft continues as an upper level
ridge of high pressure remains over the region. Expect VFR
conditions under mostly clear skies through the period. Guidance
suggests around a 50% chance for IFR conditions along the central
Oregon coast after 12z Saturday, including KONP, due to
reductions is visby with mist/fog possible. Lower chances (20%)
along the northern coast. Northwest winds increase along the coast
this afternoon with gusts up to 20 kt, while offshore winds are
developing near surface out of the Columbia River Gorge, with
gusts to around 20-25 kt near KTTD. NNE winds continue through
the central and southern Willamette Valley today, becoming more
variable overnight.

Additionally, hot temperatures are forecast, so pilots should be
aware of high density altitude and reduced aircraft performance as
a result.

PDX AND APPROACHES...VFR under clear skies expected. NW winds
expected to become ENE by 21z this afternoon, with gusts up to
15-20 kt. Winds expected to turn back to the northwest later this
evening, around 05z Saturday. Day time temperatures today and
Saturday are expected to be hot, so pilots should be aware of
high density altitude and reduced aircraft performance as a
result. /Hartsock

&&

.MARINE...Very little change in the forecast pattern through early
next week. High pressure will remain offshore over the northeast
Pacific through the remainder of the week and through the weekend.
This will maintain northerly winds across the coastal waters,
with strongest winds diurnally driven each afternoon and evening
as pressure gradients tighten. Gusts to 25 kt expected this
afternoon and evening. Small Craft Advisory conditions likely persist
into the weekend but mainly over the outer waters as the pressure
gradient shifts offshore. Seas generally remain wind driven, at
around 4 to 6 ft with a dominate period of around 8-9 seconds.
The next chance for a pattern change arrives late next week with
the potential of a low pressure system approaching the coastal
waters. /DH

&&

.FIRE WEATHER...Expect hot and dry conditions through at least
Tuesday for areas away from the coast.

Breezy easterly winds currently in place across the western
Gorge into the eastern Portland Metro and across the higher
Cascade foothills are expected to slowly weaken tonight, and
while present on Saturday won`t, be near critical levels. Still,
daytime relative humidity will low in the teens to 20s east of
the coast range.

In addition, strong nighttime thermal belts likely produce poor
overnight relative humidity recoveries across the higher
terrain through at least Sunday night, especially for elevations
above 3000 ft where maximum relative humidity values in the 20s
and 30s are forecast. Note that relative humidity values most
likely won`t follow a typical diurnal curve, as humidity values
are likely to peak in the evening before dropping rapidly
overnight.

There is also a 10-25% chance of thunderstorms over the
Willamette N.F. near the Cascade crest late Sunday through next
week during the afternoon/evening hours each day. Note that any
thunderstorm that does develop will most likely be slow moving
and wet, which would help decrease the potential for widespread
new fire starts. -Schuldt/HEC

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory until 5 AM PDT Tuesday for ORZ104-105-126>128.
     Heat Advisory until 5 AM PDT Monday for ORZ106-107.
     Extreme Heat Warning until 11 PM PDT Tuesday for ORZ108>125.
WA...Heat Advisory until 5 AM PDT Tuesday for WAZ202-211.
     Heat Advisory until 5 AM PDT Monday for WAZ203.
     Extreme Heat Warning until 11 PM PDT Tuesday for WAZ204>210.
PZ...Small Craft Advisory until 8 PM PDT this evening for
     PZZ251>253.
     Small Craft Advisory until 5 PM PDT Saturday for PZZ271>273.
&&

$$

www.weather.gov/portland

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