887
FXUS66 KPQR 111301 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
600 AM PDT Mon Aug 11 2025

...Updated aviation discussion...

.SYNOPSIS...Strong high pressure maintains hot weather weather
through Tuesday, with temperatures threatening triple digits in
the interior valleys each day. Onshore flow brings a significant
cooldown on Wednesday, with temps returning near seasonal norms
through the end of the week. Chances are increasing for
measurable rain across the area late in the week.

&&

.SHORT TERM...Now through Tuesday Night...High pressure
continues to dominate the upper level pattern this morning as
an impressive 600 decameter ridge remains anchored over the
eastern Pacific along 140W longitude. An embedded shortwave
feature is weakly apparent on water vapor imagery offshore of
the Washington and Oregon coasts, but expect this feature to
have little to no impact on sensible weather today. Temperatures
remain in the 70s across much of the interior lowlands as of 3
AM Monday, contributing to major HeatRisk across the area today.
The latest sounding from KSLE shows 850 mb temps above 23 C over
the area, with little change expected in the air mass today.
Can thus expect another day of high temperatures in the upper
90s to low 100s in the interior valleys this afternoon. NBM
probabilistic guidance accordingly shows chances to reach 100
degrees ranging from 40-60% across the Portland/Vancouver Metro
to over 90% in the central/south Willamette Valley again today.
Expect another night of lows only reaching into the mid 60s and
perhaps closer to 70 degrees in urban areas tonight into Tuesday
morning as high pressure remains in control.

The ridge will begin to retrograde westward into the open
Pacific on Tuesday, but any impacts on afternoon high temps
will be minimal as 850 mb temps remain around 22-23 C and 500 mb
height falls will be modest at best. Could therefore see highs
running a degree or two lower across the area on Tuesday, but
still generally in the upper 90s to low 100s. This is reflected
in the NBM probs which show chances to reach 100 degrees roughly
on par with today`s values across the interior valleys. The
first tangible signs of relief from the heat will more likely
come overnight Tuesday as increasing onshore flow allows lows to
drop farther into the 60s and even the upper 50s in some inland
locations. /CB

.LONG TERM...Wednesday through Sunday...Wednesday will bring
a welcome return to a cooler onshore flow regime as high
pressure is gradually replaced by upper level troughing over
western Canada. These effects will be most strongly felt across
the north on Wednesday, as the probability to reach 90 degrees
increases from 25% in the Portland area to closer to 70% around
Eugene. Still, can expect Wednesday afternoon`s highs to run
anywhere from 10-15 degrees cooler than Tuesday across the
inland valleys, with HeatRisk falling back into the minor
category as overnight lows return to more comfortable values.
Beyond Wednesday, confidence remains high that temperatures will
reside near or slightly below seasonal norms in the upper 70s
to low 80s for the duration of the week.

Precipitation chances have continued to increase next Friday
into Saturday with this forecast package as various ensemble
systems begin to latch onto the idea of deeper upper level
troughing developing over the NE Pacific and bringing another
round of measurable rain to parts of northwest Oregon and
southwest Washington. While rain is still by no means a
certainty, NBM guidance does depict a 50-60% chance for a
wetting rain of a quarter inch along northern coastal areas and
parts of southwest Washington through Saturday morning, with
probs ranging from 45% in the Portland area to around 25% in the
Eugene area. Will continue to monitor in the coming days, as
the prospect of another wetting rain would certainly be welcome
news to those with fire weather interests west of the Cascades.
/CB

&&

.AVIATION...High pressure will maintain VFR conditions with clear
skies across most of the region today. There is a 10-30% chance
for IFR/MVFR CIGs and/or VIS along the coast between 12-17z Mon
due to potential marine stratus and mist, with the highest chances
around KONP. Any stratus that forms should break out by 17-18z
Mon with daytime heating, returning VFR conditions. Guidance does
hint at marine stratus returning to the KONP area after 00z Tue,
while VFR conditions prevail elsewhere. Expect northerly to
northwesterly winds under 10 kt across the region.

Another note: with hot temperatures forecast today, be aware of high
density altitude (and reduced aircraft performance as a result).

PDX AND APPROACHES...VFR with clear skies. Northwesterly winds
under 10 kt. -Alviz

&&

.MARINE...High pressure across the waters will maintain northerly
winds through Wednesday. The breeziest winds will be this morning
with northerly wind gusts of 20-25 kt, strongest across the outer
waters beyond 10 NM. Winds gradually weaken today to around 15 kt
or less as pressure gradients ease. Expect seas around 7-9 ft at
10-11 seconds through Tuesday with a northwesterly swell. There is
a 40-60% chance that wave heights exceed 9 ft today, with the
highest chances across the outer waters. Small Craft Advisories
were extended for the outer waters through Tuesday evening, mainly
for seas. The Small Craft Advisories for the inner waters south of
Cape Falcon remain in effect through this afternoon.

A pattern change arrives on Thursday as low pressure in the
northeast Pacific shifts winds more southwesterly. Minimal impacts
expected so far with these southerly winds as guidance suggests
only a 10-20% chance for small craft conditions late this week.
                                                      -Alviz

&&

.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 5 PM PDT this afternoon for PZZ252-
     253.

  Small Craft Advisory until 11 PM PDT Tuesday for PZZ271>273.

&&

$$

www.weather.gov/portland

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