653
FXUS66 KPQR 220939
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
239 AM PDT Fri Aug 22 2025

.SYNOPSIS...Prolonged heatwave today through at least Tuesday
due to high pressure building over the region. Moderate to
Major HeatRisk for all inland locations through Tuesday with
high temperatures of 95-103F for inland valleys. Moderate to
high confidence high temperatures of 90F continue through
Wednesday. Dry and breezy conditions on Friday will lead to
near critical fire weather conditions in the eastern
Portland/Vancouver metro and Columbia River Gorge.

&&

.DISCUSSION...Friday through Thursday...A multi-day heatwave
begins today for NW Oregon and SW Washington due to strong high
pressure building into the PacNW from the Desert SW. Confidence
continues to increase that this event will last at least through
Tuesday with high temperatures over 95 to 100 degrees for
inland valleys, and the potential of temperatures above 90
degrees continues through Wednesday. In addition, overnight
lows will be running warm with many locations struggling to dip
below the upper 60s to around 70F, resulting in a Moderate to
Major HeatRisk for all inland areas. The warmest overnight lows
are expected in the Columbia River Gorge where lows in the low
to mid 70s are in the forecast due to breezy easterly winds
through the night. An Extreme Heat Warning and Heat Advisory
remain in effect from 11 AM today through 5 AM Tuesday. If you
have extended outdoor plans, especially ones that include
strenuous activity, it is important to stay extra hydrated to
avoid heat-related illness. Stay in the shade as much as
possible, and take frequent breaks. Additionally, these hot
daytime temperatures plus warm overnight lows will make it very
difficult to for buildings without air conditioning to
sufficiently cool off overnight, which could exacerbate heat
impacts in a long-duration heat event such as this one. Those
vulnerable to heat should be extra cautious.

There is extremely high confidence in ensemble guidance that
today and Saturday will be the hottest days. Most inland valleys
are forecast to reach high temperatures of 98-103 degrees with
highs in the low to upper 90s for the Cascades, Coast Range, and
Willapa Hill lowlands. Temperatures Sunday and Monday will only
be slightly lower. NBM indicates a 75-95% chance of
temperatures exceeding 95 degrees both days, and a 40-65% chance
of temperatures reaching 100 degrees (highest probability south
of Portland to Salem). For Tuesday, chances have also increased
for temperatures to exceed 95 and 100 degrees at 60-80% chance
and 30-55% chance respectively, except for slightly lower
probabilities of 40-60% chance and 10-30% chance respectively
for the SW Washington lowlands. Wednesday now has high
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.
Additionally, there`s now a 40-60% chance for high temperatures
to reach 95 degrees, which is a decent increase from the
previous forecast package. There is still decent model spread
for temperatures early next week, but the low end of the spread
remains in the low 90s through Tuesday, which would still result
in at least 5 days of temperatures over 90 degrees.

As Thursday comes into the picture, the area may finally see
some cooling. Ensemble guidance indicates the strong high
pressure could finally begin breaking down as troughing develops
in the eastern Pacific. The temperature spread is pretty large,
but the high end of the spread (instead of the low end) is in
the low to mid 90s with the mean forecast lowering inland
temperatures into the upper 80s.

In addition to the heat, dry and breezy conditions today will
lead to near critical fire weather conditions in the eastern
Portland/Vancouver metro, Columbia River Gorge, and adjacent
Cascade ridgetops. Please see the fire weather discussion below
for details.

The potential for monsoonal moisture moving into the area from
the south continues for next week, bringing increasing chances
for showers and thunderstorms in the central Oregon Cascades.
This could begin as early as Sunday afternoon in eastern Lane
County when an upper level impulse will push northward towards
the Cascades. Note that steering flow looks to be very weak,
suggesting any storms that do develop would move very slowly.
Given the high PWAT values in place (over 1"), heavy rain would
be possible with any thunderstorm that develops. As of right
now, confidence remains low regarding the exact location,
timing, and coverage of storms. NBM PoPs are generally around
10-20%, but have the potential to increase with future forecast
updates. Even if thunderstorms develop east of the Cascade
crest, there is the potential for convective cloud debris to
move west of the Cascades and impact high temperatures,
depending on the coverage and timing. -HEC/TK

&&

.AVIATION...High pressure will continue to dominate the region,
supporting mainly VFR conditions. Guidance still suggests a low
chance (20-30%) for sub-VFR conditions for KONP through 14-15z but
nothing has been observed on satellite as of 9z. Light and
variable winds overnight will increase from the northwest
after 18-21z to 10-15 kt with gusts 20 kt along the coast.

Conditions inland remain VFR with light winds overnight. Winds
increase from the north/northeast after 18z to around 10 kt with
gusts to 15 kt. Stronger winds from the east/northeast are
expected across the western Columbia River Gorge and into the
eastern metro where sustained winds could reach 15 kt with gusts
to 25 kt. 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 conditions beneath clear skies expected.
Light winds overnight will increase from the north/northeast after
18-20z. Expect winds 10-15 kt with gusts to 20 kt during the
afternoon and evening. -Batz

&&

.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. Could see wind- driven Small Craft
Advisory conditions 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. /Hartsock

&&

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

Breezy easterly winds expected through tonight for the Columbia
River Gorge and adjacent Cascade ridgetops and this morning
through this evening for the eastern Portland/Vancouver metro.
Winds will be strongest on exposed ridgetops where wind gusts
will most likely peak between 25-35 mph. Elsewhere, expect wind
gusts between 15-20 mph, except up to 30 mph in the western
Columbia River Gorge. The breezy east winds will occur
simultaneously with low relative humidity values of 20-30% or
less, resulting in near critical fire weather conditions. Use
extra caution with potential ignition sources, especially in
grassy areas. Outdoor burning is not recommended.

Strong nighttime thermal belts will 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 10-15% chance of thunderstorms over the Willamette
N.F. near the Cascade crest 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. -TK/HEC

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Heat Advisory from 11 AM this morning to 5 AM PDT Tuesday for
     ORZ104-105-126>128.

     Extreme Heat Warning from 11 AM this morning to 5 AM PDT
     Tuesday for ORZ108>125.

WA...Heat Advisory from 11 AM this morning to 5 AM PDT Tuesday for
     WAZ202-211.

     Extreme Heat Warning from 11 AM this morning to 5 AM PDT
     Tuesday for WAZ204>210.

PZ...Small Craft Advisory until 8 PM PDT this evening for
     PZZ251>253.

     Small Craft Advisory until 5 AM PDT Saturday for PZZ271>273.
&&

$$

www.weather.gov/portland

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