010
FXUS66 KPQR 242152
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
252 PM PDT Sun Aug 24 2025

.SYNOPSIS...High pressure will lead to hot and dry conditions
across interior locations east of the Coast Range, and morning
fog along the coast. Monsoonal moisture moving into the area
will bring a 15-25% chance for thunderstorms across the Cascades
today through Wednesday, especially for the Linn and Lane County
Cascades. Onshore flow continues through the end of the week,
gradually dropping temperatures closer to normal with increasing
afternoon humidity.

&&

.SHORT TERM...Now through Tuesday Night...High pressure will
maintain hot and dry conditions today with afternoon highs
forecast in the upper 90s across interior valleys and 70s along
the coast. Monsoonal moisture from upper level shortwaves to
our south is bringing in mid to high level cloud cover over the
area, which will keep us a few degrees cooler than the last two
days. Overnight lows remain forecast between 60 to 70 degrees,
warmest in the Columbia River Gorge and urban areas from Salem
northward. Most of the Extreme Heat Warnings and Heat Advisories
across northwest OR and southwest WA continue through Tuesday,
except for the Heat Advisory along the Coast Range and Willapa
Hills which is in effect until Monday morning. Continue to stay
hydrated, take precautions while outside, and check on those
most vulnerable to heat.

Increased monsoonal moisture will also lead to a slight
(15-25%) chance for thunderstorms across the Cascades today
through Wednesday. Thunderstorm chances will mainly be confined
to the Willamette National Forest (Linn and Lane County
Cascades) each afternoon, however, as monsoonal moisture
increases the next few days, thunderstorm chances (10-15%) will
may spread into the north Oregon and south Washington Cascades.
The upper level pattern is not the most robust for thunderstorm
development, as we`d typically would like to see more southerly
or slight southwesterly flow aloft to bring even more moisture
and instability. Southeasterly flow could help push any surface-
based thunderstorms into the Willamette Valley (less than 10%
chance), but soundings are also showing a capping inversion
closer to the surface that would prevent significant surface-
based convection.

If any thunderstorms form, the main threat will be lightning
and gusty outflow winds. Most thunderstorms are expected to be
wet as models are showing PWAT values between up to 1-1.25 inch
over the Cascades, which comes close to the 90th percentile of
PWATs for this time of year. Can`t rule out an isolated dry
thunderstorm or two, however, confidence is not high enough that
we would be seeing widespread abundant lightning to warrant any
fire weather headlines. The forecast these next few days is
pretty rinse and repeat with temps dropping a few degrees each
day along with afternoon thunderstorm potential.      -Alviz

&&

.LONG TERM...Wednesday through Saturday...Most ensemble guidance
are in general agreement of broad low pressure entering the
northeast Pacific from the Gulf of Alaska in the latter half of
the week. What we have high confidence in right now is that this
will maintain onshore flow, supporting the downward trend in
temperatures and increase in afternoon humidity. Temperatures
will likely fall close to normal by the end of the week, with
highs forecast in the low 80s. NBM guidance shows a 15-30%
chance for temperatures of 90 degrees or hotter Wed-Thu across
the Willamette Valley, falling to a 5-10% chance by Fri-Sat.

What there is still uncertainty on is the exact track and
magnitude of this low pressure. This leads us to a lower
confidence forecast in the long term in regards to the
specifics. As is common with the first system after a prolonged
period of high pressure, this low will act as the sacrificial
lamb causing the ridge to weaken.

Our current air mass is so dry that any precipitation that
falls from this low will initially lean towards virga, where
precipitation evaporates before reaching the surface. Areas with
orographic lift like the Coast Range and Cascades would the
highest probability of rain. The best chances for rain come on
Friday, but there`s still uncertainty on the pattern. Current
48 hour chances for 0.10" of rain or more ending 5 AM Saturday
is around 20-40% along the coast, Coast Range, and Willapa
Hills, and 10-25% across interior valleys.     -Alviz/Muessle

&&

.AVIATION...Generally VFR conditions are expected away from the
coast through the TAF period. Satellite imagery shows marine
stratus and fog hanging right along the coastline this afternoon
and while KAST was able to clear out, other sites like KONP
closer to the water likely will hold on to IFR/LIFR conditions
in perpetuity. Any coastal terminals which do see clearing will
likely (70-90%) see LIFR/IFR conditions return around 00-05Z.
VFR conditions are expected to prevail through the TAF period at
all inland sites with SCT-BKN CIGS AOA 10-25kft. Winds stay
fairly light, generally less than 10 knots.

Additional hot temperatures are expected through this afternoon
into the early evening; pilots should continue to be aware of
high density altitude and reduced aircraft performance as a
result.

PDX AND APPROACHES...Going forward expect SCT-BKN high clouds
to continue to move overhead from time to time with VFR
conditions and fairly light W-NW winds.       -Schuldt

&&

.MARINE...A fairly stable summertime pattern is expected through
the middle of the week as a surface high pressure remains
offshore over the eastern Pacific. This feature will help to
maintain northerly winds tonight into late Wednesday although it
appears frequent gusts exceeding ~20-21 knots hold right along
the edge of the outer waters each afternoon and evening. Given
the marginal nature of these winds, have held off from issuing
any Small Craft Advisories. It`s also worth noting we`ll need to
keep an eye on marine fog during the evening, overnight, and
early morning hours the next few days which may reduce
visibility below 1/2 mile. Seas generally remain driven by a
fresh northwesterly swell, at around 4 to 6 ft, with a dominate
period of around 7-9 seconds. The next chance for a pattern
change arrives on Thursday into Friday with a low pressure
system approaching the coastal waters resulting in a southerly
wind switch.      -Schuldt

&&

.CLIMATE...
Daily record high temperatures:

Sunday, August 24

Portland   99 (1982)
Vancouver 100 (1988)
Hillsboro 101 (1958)
McMinnville 100 (1916, 1926)
Salem  99 (1958)
Eugene  96 (1958, 1982, 2010)

Monday, August 25

Portland  95 (2016)
Vancouver  96 (1982, 2010)
Hillsboro  96 (1982, 2010, 2016)
McMinnville  98 (1916, 1996)
Salem  97 (1967, 2016)
Eugene  97 (2010, 2016)

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Heat Advisory until 5 AM PDT Tuesday for ORZ104-105-126>128.

     Heat Advisory until 5 AM PDT Monday for ORZ106-107.

     Extreme Heat Warning until 11 PM PDT Tuesday for ORZ108>125.

WA...Heat Advisory until 5 AM PDT Tuesday for WAZ202-211.

     Heat Advisory until 5 AM PDT Monday for WAZ203.

     Extreme Heat Warning until 11 PM PDT Tuesday for WAZ204>210.

PZ...None.

&&

$$

www.weather.gov/portland

Interact with us via social media:
www.facebook.com/NWSPortland
x.com/NWSPortland