Excessive Heat in Oregon, August 10 to 12, 2025

Area Forecast Discussion
National Weather Service Portland OR
344 AM PDT Sun Aug 10 2025

.SYNOPSIS...Strong high pressure over the eastern Pacific will
yield hot temperatures today through Tuesday. Extreme
Heat Warnings and Heat Advisories remain in effect. Fortunately,
conditions return closer to normal on Wednesday with a cooling
trend into the end of the week.

&&

.SHORT TERM...Now through Tuesday Night...The dominant feature
on water vapor imagery this morning is a stout upper level ridge
of high pressure which encompasses much of the eastern Pacific,
with the ridge axis running roughly parallel to 140W longitude.
A stretch of well above normal temperatures will commence
across northwest Oregon and southwest Washington today as this
ridge continues to strengthen offshore, sending 850 mb temps
soaring into the 21-23 C range over our area - well above the
90th percentile of early August KSLE sounding climatology. These
values will correspond to surface temperatures climbing well
into the 90s in the interior valleys this afternoon, with
chances for the first triple digit readings of the season
ranging from 25-35% across the Portland/Vancouver Metro to
about 70-80% in the central/south Willamette Valley. The
combination of well above normal high temps along with
overnight lows running in the upper 60s to perhaps 70 degrees in
some urban areas will drive NWS HeatRisk into the major
category across a wide swath of the area today through Monday,
with the current Extreme Heat Warnings and Heat Advisories going
into effect today at noon. One other factor to consider today
will be the potential for locally critical fire weather concerns
in parts of the Willamette Valley this afternoon. These
concerns are discussed in greater detail in the fire weather
section below.

Models continue to exhibit slightly larger forecast spreads with
respect to high temps on Monday, due in large part to the
presence of a developing weak shortwave feature embedded in the
eastern periphery of the ridge. Most of the guidance continues
to suggest any sensible weather impacts associated with this
feature would be minimal, with probabilities to reach 100
degrees ticking upwards to 15-25% in the Cowlitz Valley 40-60%
in the Portland/Vancouver Metro, and 85-95% in the central/south
Willamette Valley for Monday afternoon. Still, a slightly
stronger shortwave feature and the minor boost in onshore flow
it would provide could spell the difference between highs in
the mid to upper 90s vs the low triple digits from the
Portland/Vancouver Metro to parts of southwest Washington,
producing a small but non trivial difference in terms of
HeatRisk impacts in some of these locations on Monday.

The pattern shows signs of breaking down on Tuesday as the
ridge retrogrades farther offshore into the open Pacific.
However, confidence continues to increase that the heat will
hang on for one more day as the arrival of a stronger shortwave
trough over the Pacific Northwest is delayed until Tuesday night
or Wednesday morning. As a result, temperature guidance on
Tuesday now reflects values more similar to today and Monday,
with NBM probs to reach 100 degrees holding at 15-25% in the
Cowlitz Valley 40-60% in the Portland/Vancouver Metro, and
70-80% from Salem to Eugene through Tuesday afternoon. Latest
guidance suggests this could potentially keep HeatRisk in the
Major category in some locations through Tuesday. /CB

.LONG TERM...Wednesday through Saturday...The aforementioned
shortwave trough will move across the region Tuesday night or
Wednesday, opening the door to a cooler onshore flow regime
during the latter half of the week. Inland high temperatures
will drop back into the 80s on Wednesday, with relatively high
confidence that temperatures will remain near or slightly below
seasonal norms in the upper 70s to low 80s through the end of
the week. There is no precipitation in the forecast for
the next seven days, with the exception of a slight chance along
the south Washington coast with the arrival of onshore flow late
in the week. Will mention that the Euro AIFS ensemble appears
rather bullish on chances for more widespread rain returning to
the region next weekend, which is notable in that this was the
first model suite to catch on to the rain event that occurred
back on August 6. Something to monitor moving forward. /CB

&&

.AVIATION...Satellite imagery as of early Sunday morning shows
marine stratus along the coast bringing a mix of LIFR/IFR/MVFR
CIGs to coastal terminals. Expect these lower CIGs to continue
along the coast through 17-19z Sun, with intermittent clearing to
VFR around KONP. Mist may also reduce visibility to MVFR
thresholds at times along the coast through 18z Sun, especially
at KONP. CIGs and/or VIS along the coast should improve to VFR by
19-20z Sun as daytime heating progresses. High pressure will
maintain VFR conditions with sunny skies across Willamette Valley
terminals through the TAF period. Northerly to northwesterly winds
across the region will be strongest in the afternoon with gusts
up to 20-25 kt.

PDX AND APPROACHES...VFR with clear skies. Northwesterly winds
under 10 kt through 20-21z Sun, then increasing to 10-15 kt with
gusts up to 25 kt through the evening. 	-Alviz

&&

.MARINE...High pressure across the waters will maintain northerly
winds across the waters through at least Thursday. Tighter
pressure gradients today will lead to increased winds, strongest
in the afternoon and evening with northerly wind gusts to 25-30
kt. In the latest update, the Small Craft Advisory was expanded
into the inner waters north of Cape Falcon (out 10 NM) from
1400 Sunday to 2300 Sunday. Small Craft Advisories remain in
effect across the rest of the waters through Monday afternoon.
Winds ease overnight.

Expect wind-driven, choppy seas around 6-7 ft at 10 seconds today,
building to 8-11 ft at 10 seconds on Monday as a northwesterly
swell moves in. Wave heights will be highest across the outer
waters. The inner waters north of Cape Falcon remain out of the
Small Craft Advisory on Monday for now, however, will continue to
monitor the incoming swell today to see if this zone will become
hazardous to small craft. 	-Alviz

&&

.FIRE WEATHER...Enhanced fire weather concerns will exist in
parts of the Willamette Valley today as the orientation of a
strengthening thermal trough along the west slopes of the
Cascades yields breezy north winds. Still do not anticipate
widespread critical fire weather conditions being met, but the
combination of minimum RH values in the low 20s and north winds
gusting to 15-20 mph does raise the possibility that conditions
will flirt with Red Flag criteria in the central/south valley
for a few hours this afternoon. Lighter winds will help to limit
fire weather concerns on Monday. /CB

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory from noon today to 10 PM PDT Tuesday for ORZ104-
     105-108.

     Extreme Heat Warning from noon today to 10 PM PDT Tuesday for
     ORZ109>125.

WA...Heat Advisory from noon today to 10 PM PDT Tuesday for WAZ202-
     204-208.

     Extreme Heat Warning from noon today to 10 PM PDT Tuesday for
     WAZ205>207-209-210.

PZ...Dense Fog Advisory until 11 AM PDT this morning for PZZ210-
     251>253.

     Small Craft Advisory from 2 PM this afternoon to 11 PM PDT this
     evening for PZZ251.

     Small Craft Advisory until 5 PM PDT Monday for PZZ252-253-
 	 271>273.

&&

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