406
FXUS66 KPQR 231006
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
306 AM PDT Sat Aug 23 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 96-106F 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. Thunderstorms for
the central Oregon Cascades are also a growing concern for late
Sunday onward, though confidence in exact placement and timing
is only low to moderate beyond the broad set-up.

&&

.DISCUSSION...Saturday through Friday...The heat is on!
Yesterday kicked off the heatwave with six climate stations
breaking or tying daily high temperature records: Portland,
Hillsboro, McMinnville, Salem, and Eugene all broke their
records and Vancouver tied theirs. Similar high temperatures are
expected today and Sunday across NW Oregon and SW Washington
with inland valleys peaking around 97-103 degrees today and
96-100 degrees Sunday. A number of daily high temperatures
records are in jeopardy again both days. Those records are
listed in the Climate section below.

The strong upper level high pressure and associated surface
thermally induced trough causing the well-above normal
temperatures are slated by ensemble guidance to begin weakening
slightly Monday into Tuesday. This will allow daytime
temperatures to lower slightly. This will be most notable in the
Coast Range, Willapa Hills, and Cascades where daytime
temperatures will fall back into the 70s to 80s. However, inland
valleys are still expected to remain hot. NBM still indicates
high confidence (70-95% chance) of temperatures remaining above
90 degrees both days. Additionally, moderate to high confidence
remains for temperatures to reach or exceed 95 degrees with a
60-85% chance, slightly higher on Monday than Tuesday and for
the Portland/Vancouver metro area and south. Wednesday is
expected to remain warm with inland valleys over 90 degrees, but
chances of temperatures reaching 95 degrees are now around
25-50%. Overnight temperatures are expected to remain on the
warm side every night through Tuesday night. Most inland
locations will remain above 60-68 degrees, warmer north of
Salem, with the Columbia River Gorge remaining above 70 degrees.
Widespread Moderate to Major HeatRisk continues through
Wednesday. The combination of hot daytime temperatures plus warm
overnight lows make it very difficult 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, a surge of monsoonal moisture will move into
Oregon from the desert southwest/California Sunday into next
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, but 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 that high level convective debris from any
thunderstorms may impact/decrease high temperatures, depending
on the coverage and timing.

Ensemble guidance indicates the strong high pressure
finally begins breaking down Thursday and Friday as troughing
develops in the eastern Pacific. Temperatures will finally fall
back into the 80s inland, if not Thursday then by Friday.
Onshore flow is expected to return along with marine stratus.
There are early indicates of the potential for rain to return,
though chances are very low (10-20%) as there are significant
differences in ensemble members for the general progression of
the trough. Either way, the region will finally see relief from
the heat by late week. -HEC/Schuldt


&&

.AVIATION...Upper-level ridging continues, bringing VFR
conditions through most of the TAF period. The only exception:
low to moderate confidence for fog/mist to reduce VIS/CIG at
coastal terminals 12Z Saturday (IFR/LIFR chances: 30-40% at KAST
and 40-60% at KONP). There is moderate confidence that the coast
will return to VFR by 18Z Saturday, with a 10-20% chance that MVFR
will linger instead. By 00-03Z Sunday, conditions will once again
deteriorate along the coast (20-40% chance of IFR). Otherwise,
expect westerly winds under 10 kt.

Inland, clear skies, VFR conditions, and mostly northwesterly
diurnally-driven winds under 10 kt are expected. Hot temperatures
are forecast, so pilots should be aware of high density altitude
and reduced aircraft performance as a result.

PDX AND APPROACHES...Clear skies, VFR conditions, and mostly
northwesterly diurnally-driven winds under 10 kt are expected.
Wind direction could briefly shift easterly between 18Z Saturday
and 00Z Sunday, but winds will remain relatively light. ~Hall

&&

.MARINE...Very little change in the forecast pattern through early
next week. High pressure will remain offshore over the northeast
Pacific 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 are expected in the outer waters, so a Small Craft
Advisory remains in effect until this evening. Could see Small
Craft conditions continue into tomorrow, but will likely weaken
enough to stay out of most of each outer water zone. 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. ~Hall/DH

&&

.CLIMATE...
Daily record high temperatures:

Saturday, August 23

Portland 101 (1988)
Vancouver  95 (2000)
Hillsboro  97 (1996)
McMinnville 103 (1988)
Salem 102 (1988)
Eugene  98 (1911)

Sunday, August 24

Portland   99 (1982)
Vancouver 100 (1988)
Hillsboro 101 (1958)
McMinnville 100 (1926)
Salem  99 (1958)
Eugene  96 (2010)

&&

.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 5 PM PDT this afternoon for
     PZZ271>273.

&&

$$

www.weather.gov/portland

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