758
FXUS66 KPQR 102132
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
232 PM PDT Sun Aug 10 2025

.SYNOPSIS...Increasing high pressure with a thermal trough
forming over the Pacific Northwest will lead to intensifying
temperatures through Tuesday. A cooling trend will start on
Wednesday as stronger northwesterly flow develops. For those
wanting rain, there appears to be an incoming system later in
the week that may deliver rainfall to the area.

&&

.SHORT TERM...Now through Tuesday Night...Synoptically, the next
few days will be dominated by an anchored strong high pressure
system. This high will usher in warmer air from the south
causing temperatures to increase significantly. Today thus far,
temperatures have risen into the low 90s throughout the
Willamette Valley and into the 60s along the coast. Warm
conditions persist through the Cascade Valleys where
temperatures near 85-90 degrees F have been reported. Will
continue to see temperatures rise with them reaching nearly 100
degrees F today in the lowlands. With these types of
temperatures, a thermal trough will form near the surface. A
thermal trough forms when the air is so warm that it causes air
to rapidly rise and thus creates an area of temperature induced
low pressure. In this type of pattern, northerly winds are the
most common. This afternoon, the northerly winds will increase
through the Willamette Valley leading to gusts around 20-25 mph
in areas from Corvallis southward, and along the coast. Coupled
with the warm temperatures during the day, temperatures will
stay elevated overnight.

The combination of the high daytime and night time recovery
temperatures, the duration of the heat, and the high dew point
temperatures, much of the Willamette Valley and south Washington
Valleys sit in Major HeatRisk, and the Coast Range Valleys,
Lower Columbia, and Cowlitz Valleys are in a Moderate HeatRisk.
This leads to two different hazards being issued: an Extreme
Heat Warning for the Willamette Valley and the Gorge, and a Heat
Advisory in other interior valleys west of the Cascade
foothills.

Heat continues on Monday, with increasing probabilities of
temperature meeting or exceeding 100 degrees F inland. Monday is
slated to be the hottest day of the week as it will be day 3 of
the thermal trough development and thus the compounding factor
of multiple days of heat. Overnight, there was a shift in the
Tuesday high temperatures which remains consistent with latest
model runs. Let`s dive into some of the numbers. In Eugene on
Monday, the general box of the box and whisker plot which
represents the 25th-75th percentile is around 103-105 degrees F.
However, the 90th percentile is close to 110 degrees F (around
a 10% chance), and the 10th percentile (also a 10% chance) is
around 100 degrees. On the lower end of that range the numbers
are fairly consistent however there is still quite a spread.
Based on the overall trends, have leaned into values closer to
the 10th-25th percentile for high temperatures on Monday.
Looking at Tuesday, the same ranges (10th-90th, and 25th-75th
percentile) go from 97-110 degrees (10th-90th) and 99-103
degrees (25th-75th). Overall, while the spread is still high,
there is high confidence that we will exceed 100 degrees around
Eugene. While other areas are not quite as hot, the overall
trend remains consistent with the probabilistic spread.

As Tuesday comes to an end, a low pressure system in the Gulf of
Alaska will push into Canada. This will extend weak shortwave
troughs over the area overnight into Wednesday. More details
below! -Muessle


.LONG TERM...Wednesday through Sunday...The aforementioned
shortwave trough will move across the region Tuesday night
through 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. If you`re wanting a break from the
hot sunny weather, there has been a major shift in the forecast
that may make those wishes come true. On Thursday into Friday
morning, a low pressure system coupled with a low aloft will
shift into the Northeast Pacific. On Thursday onshore flow will
intensify causing winds to increase from the west. But Friday
will be a day of rain...yes...rain. Rain probables are highest
along the coast and from Marion County northward. Overall, there
is quite a bit of uncertainty as it will greatly depend on
where the low moves. If it shifts northward, more areas of our
forecast area will miss out on the rain, but if it shifts south,
the opposite is true. If rain does occur, it will last through
much of the weekend. -Muessle


&&

.AVIATION...High pressure will maintain VFR conditions with sunny
skies across most of the region through the TAF period. Only
exception is a 50% chance of MVFR/IFR ceilings along the coast
between 09-18z Monday as a band of marine stratus is expected to
form just off the coast. The main uncertainty is whether the
stratus will push onshore to the terminals or if it will remain
offshore. Increased northerly to northwesterly winds with gusts
up to 20-25 kt, decreasing after 00-06z Mon to sustained winds
less than 10 kts.

PDX AND APPROACHES...VFR with clear skies. Northwesterly winds
10-15 kt with gusts up to 25 kt, decreasing after 03-06z Mon. -HEC

&&

.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. Winds slowly ease overnight into Monday afternoon. Small
Craft Advisories remain in effect across the rest of the waters
through Monday afternoon.

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 to see if this zone will become
hazardous to small craft. -Alviz/HEC

&&

.FIRE WEATHER...Enhanced fire weather concerns will exist in
parts of the Willamette Valley this evening 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. Based on area observations as of
1400, winds have generally remained below criteria. However,
they are still breezy which may create localized complications.
Will note though that overnight humidity recoveries will be
high. Lighter winds will help to limit fire weather concerns on
Monday. -CB/Muessle

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Heat Advisory until 10 PM PDT Tuesday for ORZ104-105-108.
     Extreme Heat Warning until 10 PM PDT Tuesday for ORZ109>125.
WA...Heat Advisory until 10 PM PDT Tuesday for WAZ202-204-208.
     Extreme Heat Warning until 10 PM PDT Tuesday for WAZ205>207-
     209-210.
PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ251.
     Small Craft Advisory until 5 PM PDT Monday for PZZ252-253-
     271>273.
&&

$$

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