574
FXUS66 KPQR 212226
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
326 PM PDT Thu Aug 21 2025

.SYNOPSIS...High pressure will continue building over the region
through the weekend, bringing a prolonged stretch of hot and dry
weather with Moderate to Major HeatRisk for inland valleys
Friday through Monday with high temperatures of 95-103F.
High confidence high temperatures of 90F or warmer continue
through early to mid next week. 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...Thursday night through Wednesday night...A significant
warmup begins tomorrow, marking the beginning of a prolonged period
of hot and dry weather with record high temperatures likely to occur,
except at the coast where temperatures will be much cooler. This
pattern shift is in response to an upper level ridge of high pressure
centered over the Four Corners region, which will be building
northward into the Pacific Northwest this weekend.
Meanwhile, a thermally induced surface trough in southwest
Oregon will shift northward over the Willamette Valley Thursday
night into Friday with high pressure east of the Cascades. This
set-up will result in offshore flow, causing an increase in north
to northeast winds for the Willamette Valley later this afternoon and
evening and easterly winds in the Cascades and Columbia River
Gorge tonight into Friday morning. Max wind gusts are still
forecast to reach 20-25 mph, except 30-35 mph in the western
Gorge and along exposed Cascade ridgetops. This will lead to elevated
fire weather concerns in some areas, which is discussed below in the
fire weather discussion.

Confidence remains high extreme heat will impact areas away from the
coast Friday through at least Monday. Forecast high temperatures on
Friday and Saturday have warmed another degree or two for most
locations, which still looks to be the hottest two days. Expect high
temperatures between 96-103F both days for inland valleys. Even the
Coast Range lowlands and Cascade valleys below 3500 feet are expected
to reach 95-100F. Overall model spread remains minimal, suggesting
confidence is high temperatures within this range will materialize.
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 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. NBM temperature guidance seems reasonable given the set-up
in place and the transition to low-level offshore flow. Note dry and
breezy conditions on Friday 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.

Although model spread increases early next week, forecast confidence
continues to increase for high temperatures above 95 degrees on
Monday, and possibly into Tuesday. Probabilities for this have
increased to 65-90% on Sunday, remain near 55-75% on Monday, but have
increased to 55-75% on Tuesday (except 25-35% in the Cowlitz Valley
and lower Columbia). Probabilities for highs above 95 have increased
considerably on Wednesday as well, now ranging between 35-55%, except
20-30% in the Cowlitz Valley and less than 10% in the lower Columbia.
 These probabilities indicate there is still considerable uncertainty
regarding the exact duration of this heat event and when it will end.

Despite uncertainty regarding the end date of this heat event,
confidence remains high enough in the short term to warrant the
continuation of an Extreme Heat Warning for the Portland/Vancouver
metro area through the central/southern Willamette Valley, Oregon
Cascade foothills, Columbia River Gorge, lower Columbia, Cowlitz
Valley, and Upper Hood River Valley. A Heat Advisory remains in
effect for the Cascades below 3500 feet, the Coast Range valleys, and
lower elevations in the Willapa Hills. Both the Warning and Advisory
are in effect from 11 AM Friday 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.

Another thing that comes into play Sunday into early next week is the
potential for monsoonal moisture moving into the
area from the south, 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 15% or less, 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. -TK/HEC

&&

.AVIATION...Dry southwesterly winds aloft as upper level ridge of
high pressure builds over the region. Expect VFR conditions under
mostly clear skies through the period. North to northwest winds
increase this afternoon with gusts to 20-25 kt along the coast.
Winds ease overnight, becoming light and variable. There is a 50%
chance of reduced visby at KONP after 12z Friday due to mist.

PDX AND APPROACHES...VFR and clear skies expected through the
period. Northwest winds increase this afternoon with gusts up to
15-20 kt. /DH

&&

.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 25-30 kt are expected this
afternoon and evening before dropping to 20-25 kt tonight.
Conditions on Friday are expected to be similar with peak wind
gusts slightly lower than Thursday, likely around 25 kt. So, have
extended the Small Craft Advisories through Friday 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 today through at
least Tuesday for areas away from the coast. Critical fire
weather conditions are expected to occur over the southern
Willamette Valley through 7-8 PM this evening due to dry and
windy conditions. Until then, expect northerly winds
sustained around 15 mph with gusts up to 25 mph. Relative
humidity values will fall as low as 20-25%. Main concern is for
rapid fire spread with any grass fire that may ignite. A Red
Flag Warning remains in effect for Oregon fire weather zone 685
through 8 PM PDT Thursday to cover this threat.

Breezy easterly winds will develop Friday morning and continue
through Friday evening for the eastern Portland/Vancouver metro,
and through Friday night for the Columbia River Gorge and adjacent
Cascade ridgetops. 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 Thursday
night through at least Saturday 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 early 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 Friday to 5 AM PDT Tuesday for ORZ104-
     105-126>128.

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

     Red Flag Warning until 8 PM PDT this evening for ORZ685.

WA...Heat Advisory from 11 AM Friday to 5 AM PDT Tuesday for WAZ202-
     208-211.

     Extreme Heat Warning from 11 AM Friday to 5 AM PDT Tuesday for
     WAZ204>207-209-210.

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

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

$$

www.weather.gov/portland

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