336
FXUS66 KPQR 300436 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
936 PM PDT Fri Aug 29 2025

Updated aviation discussion.

.SYNOPSIS...A low pressure system remaining just offshore over
the Eastern Pacific will bring onshore flow, morning stratus,
and cooler daytime temperatures through Monday. Building high
pressure Tuesday through Thursday will bring warming
temperatures, with moderate confidence that temperatures will
warm at least above 90 degrees. Widespread Moderate to areas of
Major HeatRisk are possible next week.

&&

.SHORT TERM...Friday through Sunday...Visible satellite imagery
this afternoon shows mostly clear skies, which is very different
from this morning when marine stratus covered the coast and much
of the inland areas. The marine stratus didn`t dissipate until
nearly midday inland, which has kept temperatures today cooler
than originally forecast. Temperature observations at 3 PM range
from the mid to upper 70s across the inland valleys that were
impacted by the marine stratus to low to mid 80s across the
Cascades that were not impacted by the marine stratus.

The stratus intrusion was caused by increased onshore flow due
to a low pressure system situated over the Eastern Pacific. This
low pressure system will slowly inch a little bit closer to the
Oregon coast on Saturday, then slowly move slightly north off of
the Washington coast on Sunday, never actually moving inland.
Onshore flow will continue under this pattern with slightly
increased humidities and stratus likely each day. Surface winds
will remain relatively light and diurnal, westerly to
northwesterly in the afternoon, then weakly easterly overnight.
Westerly winds gusts up to 15-20 mph are possible in the
afternoons through Coast Range Gaps and along the Columbia
River. High temperatures are expected to peak in the low to mid
80s for inland valleys each day. -HEC

.LONG TERM...Monday through Thursday...Ensemble guidance
indicates the upper level low pressure system offshore will
begin moving northwest back over the Eastern Pacific with high
pressure beginning to push west into Oregon. Monday`s weather
will be similar to the weekend.

Tuesday through Thursday, ensemble guidance is coming into
better agreement that strong high pressure will continue
building west over Oregon and Washington, which would allow for
a potentially significant warming trend. However, what is
throwing a wrench in the confidence of this warming trend is a
compact closed low that is the remnants of a tropical
disturbance currently located west of Mexico. The GFS, Euro, and
Canadian ensembles all show this negatively tilted low moving
onshore in central California sometime late Monday into early
Tuesday then moving north towards Oregon on Tuesday. However,
what happens with this low Tuesday and beyond is still extremely
uncertain. It could dissipate as it reaches the Oregon border on
Tuesday, or it could continue somewhere into Oregon. If it
dissipates, temperatures could warm into the upper 90s to even
low 100s across NW Oregon and SW Washington. If the low holds
into Oregon, it could bring cloud cover that could dampen
temperatures from rising much past 90 degrees. Latest NBM
guidance (13z run) indicates a 60-85% chance of temperatures
exceeding 90 degrees Tuesday - Thursday for inland valleys,
highest probabilities south of Portland. Additionally, NBM
indicates a 50-70% chance of temperatures exceeding 95 degrees
Wednesday and Thursday, highest chances south of Portland. If
this warmer solution holds, overnight temperatures would be on
the warmer side too with most locations remaining above 60
degrees and possibly above 65 degrees for locations north of
Salem. These temperatures are producing widespread Moderate to
Major HeatRisk.

If the closed low moves north into Oregon, that would also
produce a chance of showers and thunderstorms sometime Tuesday
into Thursday. However, confidence is extremely low in where in
Oregon showers and thunderstorms would even be possible, let
alone if they could happen at all. Latest forecast keeps them
well out of our forecast area, but it still bears to mention
there`s about a 5% chance or so of this solution along the
central Oregon Cascades. -HEC

&&

.AVIATION...At 0430z Saturday, satellite and surface weather
observations showed a marine stratus deck with MVFR cigs around
1500 ft filling in along the coast, already impacting KONP and
likely impacting KAST by 07z Saturday. Although inland areas
remain mostly clear, expect a trend similar to last night with
marine stratus with MVFR cigs most likely filling in over the
southern and northern Willamette Valley towards 12z Saturday
before scattering out around 18z Saturday. Probabilities for cigs
below 3000 ft peak around 40-50% for all inland terminals around
sunrise, with KEUG, KTTD and KPDX having the highest chance. Low
pressure offshore will bring increasing chances for light rain
showers at the coast beginning around 00z Sunday, with KAST having
a higher chance than KONP. However, aviation impacts are not
expected with this showers.

PDX AND APPROACHES...MVFR cigs will most likely redevelop towards
sunrise before scattering out around 18z Saturday. The probability
for cigs below 3000 ft is near 50% during that time. Otherwise,
expect VFR flight conditions with northwest winds between 5-10 kt.
-TK

&&

.MARINE...Benign conditions will continue over the coastal waters
through the upcoming weekend as winds remain around 10 kt or less
and seas hover between 2 and 4 ft, resulting in conditions that
are favorable for small craft. A more typical summertime pattern
returns on Monday and likely continues through at least Wednesday
of next week, bringing persistent northerly winds that are
strongest during the afternoon and evening hours each day,
especially to the south of Cape Falcon. The probability of
reaching small craft advisory level wind gusts of 21 kt or
stronger is around 40-50% each day due to a relatively weak
surface pressure gradient in place. Seas should remain less than 5
ft on Monday before increasing to 5 to 6 ft late Tuesday into
Thursday. -TK/HEC

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

&&

$$

www.weather.gov/portland

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