643
FXUS66 KPQR 010445 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
945 PM PDT Wed Sep 30 2026

...Updated aviation discussion...

.SYNOPSIS...A building ridge of high pressure will lead to a warming
trend through this weekend. Expect above average temperatures with
dry conditions through the first week of October. Patchy morning fog
at times across inland valleys will be possible, before offshore
winds develop Saturday and Sunday. Otherwise, little in the way of
weather impacts through the middle of next week.

&&

.DISCUSSION...Now through Tuesday Night...Current satellite imagery
shows a few lingering clouds giving way to mostly sunny skies this
afternoon as a broad ridge of high pressure develops over the
region. Near average temperatures for the end of September will be
followed by a warming trend through the weekend as we move into
October. A weak weather system is expected to remain north of the
area as it moves toward Vancouver Island Thursday and Friday. This
feature will also keep a flatter ridge over the region with high
clouds streaming across the area. 850 mb temperatures are also
gradually warming a few degrees, which will in turn allow afternoon
highs to warm into the mid to upper 70s across the interior
lowlands through Friday.

Due to decent clearing during the overnight/morning hours, light
winds, and a more prominent temperature inversion developing each
night, patchy fog development is likely, especially in our more
protected valley areas with a water source. Morning fog will greatly
reduce visibility wherever present.

Expect temperatures to jump a few more degrees over the weekend as
the upper level ridge amplifies over the Pacific NW along with
mostly sunny skies each afternoon. Temperatures will likely warm
into the upper 70s to lower 80s on Saturday before warming a few
more degrees, into the lower to mid-80s on Sunday. Most areas are
not expected to reach record high temps, but the record of 84
degrees on Sunday at PDX could be in jeopardy. Offshore flow could
also bring slightly warmer temperatures to the coast as well with
highs into the upper 60s to lower 70s.

Underneath this upper-level ridge pattern, ensembles indicate a
near surface thermal trough develops along the coast on Friday
through this weekend. This pattern is expected to cause winds to
shift from the onshore (westerly) pattern the area has
generally been observing over the past couple of weeks to offshore
(east to northeasterly). At this time, pressure gradients do not
look to be very high, peaking at a -3mb to -4mb difference between
PDX and DLS, so winds aren`t expected to be strong. Instead, expect
to see a typical diurnal behavior of winds becoming easterly on the
west side of terrain (mainly Cascades, potentially coast range peaks
as well) in the overnight to morning hours and increasing to peak
gusts up to 20-35 mph. Then, winds decrease over the terrain during
the day and increase through the valley from the north in the
afternoon hours with gusts up to 20 mph. The probability of wind
gusts peaking above 30 mph is less than 10-25% everywhere except for
through the western Columbia River Gorge and surrounding terrain at
50-65%, which is generally the windiest location during offshore
flow. At least confidence is moderate to high regarding the
transition back to onshore flow Sunday night into Monday which would
bring an end to these drier and locally breezy conditions.

By Monday, the vast majority of ensemble members indicate the ridge
axis shifts east of WA and OR, allowing for increased onshore flow.
Temperatures should lower again into the 70s for the interior
valleys, though still remaining somewhat above normal, with dry
weather continuing through the middle of next week.  DH/99

&&

.AVIATION...Through 06Z Friday...Satellite imagery and terminal
observations as of late Thursday evening depicts VFR conditions
with SCT/BKN high clouds. Chances for MVFR stratus at any
terminal is around 5-15% at any given hour between 10-17z Fri,
with the highest chances along the coast and KEUG. High pressure
over the region will maintain predominately VFR conditions with
high clouds through the TAF period. Variable winds under 5 kt
overnight become north/northwesterly and increase to 5-10 kt in
the afternoon, strongest in the central and southern Willamette
Valley.

KPDX AND APPROACHES...VFR with high clouds and northwesterly
winds 2-5 kt continue through the TAF period.       -10

&&

.MARINE...Calmer conditions over the waters continues today, with
wave heights around 5 to 6 feet. A weak weather system out of the
west will approach the northern waters late Thursday, temporarily
shifting winds out of the west and increasing them slightly.
Northerly winds then return Friday, likely persisting through the
weekend into early next week. Otherwise, the west to
northwesterly swell of 5 to 6 ft at 9 to 11 seconds today will
gradually subside to around 3 to 4 ft Thursday and continue into
the weekend. There is no other prominent swells of note at this
time. ~12/99

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

$$

www.weather.gov/portland

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