023
FXUS66 KPQR 020455 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
955 PM PDT Thu Oct 1 2026

...Updated aviation discussion...

.SYNOPSIS...Dry weather persists going forward accompanied by a
warming trend into the weekend as a ridge of high pressure
builds overhead - well above normal temperatures by Sat/Sun.
Expect patchy morning fog at times across inland valleys as
well, although offshore winds develop Saturday and Sunday may
limit the coverage of fog somewhat. Otherwise, little in the way
of weather impacts through at least the middle of next week.

&&

.DISCUSSION...Now through Wednesday...Dry conditions and above
average temperatures will be the story to start October. Ridging
is currently centered over the Great Basin with a weak short
wave passing over Vancouver Island is keeping the ridge
suppressed over the PacNW. Upper level cloud cover can be seen
streaming in overhead along westerly flow will continue through
much of the day. Temperatures today are expected to top out 4-6
degrees warmer than yesterday (Wednesday), topping out in the
mid to upper 70s across the interior lowlands. Chances to reach
80 remain around 15-30% for the Willamette Valley with higher
chances of 40-50% across the Portland Metro.

Tomorrow is expected to be very similar to today with patchy fog
possible tonight and stratus developing along the coast. Highs are
expected to top out in the mid to upper 70s with lower probabilities
of reaching 80 as 850 mb temperatures across the area drop a degree
or two.

Heading into the weekend, the upper level ridge is expected to
amplify into the PacNW, supporting a noticeable warm-up both days.
850 mb temperatures are expected to jump into the 14-20 C range on
Saturday and between 17-22 C on Sunday. This is expected to
translate to Saturday highs in the upper 70s to low 80s across the
interior lowlands and mid 60s to low 70s along the coast. Sunday
highs jump up into the low to mid 80s inland while coastal areas see
similar temperatures to Saturday. Most areas are not expected to
reach record high temps, but the relatively weak 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 over the next several
days, ensembles continue to support the development of a surface
thermal trough along the coast on Friday through this weekend. This
is expected to shift winds from onshore (westerly) to offshore
(easterly)  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 tops of the coast range as
well) during the overnight to morning hours, increasing to peak
gusts up to 20-35 mph. Then, as mixing gets underway and the
inversion breaks, 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. Exploring the NBM, the probability of wind
gusts peaking above 30 mph is less than 10-25% everywhere except in
the western Columbia River Gorge and surrounding terrain at 40-55%,
which is generally the windiest location during offshore easterly
flow.

Throughout the end of the week into the weekend the combination of
overnight clearing/longer nights, locally lighter winds, and a
fairly prominent temperature inversion will facilitate fog
development. But, the placement of valley fog likely shifts to some
of our more protected valley areas over the weekend as the
previously mentioned offshore flow develops - this is a point of
notable forecast uncertainty. Should the overnight offshore
flow/east winds end up weaker or decoupled from the boundary layer
over the Willamette valley, fog end up fairly decent in coverage.
The REFS and even the ECMWF points to this foggier scenario playing
out at least on Saturday morning. Wherever present, fog will greatly
reduce visibility and may potentially impact travel.

By Monday, the vast majority of ensemble members indicate the ridge
axis shifts east of WA and OR, allowing the overall flow to turn
back onshore while bringing an end to the locally breezier east
winds. Temperatures lower again into the 70s to near 80 for the
interior valleys Monday afternoon into the middle of the week,
though we`ll remain generally 5 to 10 above normal for early
October. For better or worse, ensemble guidance is adamant in the
continuation of dry weather through the middle of next week,
potentially longer.       -19/99

&&

.AVIATION...Through 06Z Saturday...Satellite imagery and terminal
observations as of late Friday evening depicts VFR conditions with
high clouds over the region. Low pressure offshore will support a
marine layer pushing into the coast tonight, however, there is
uncertainty with how low CIGs will get. While marine stratus hasn`t
reached the Oregon coast yet as of 05z Fri, observations from KUIL
in the Olympic Peninsula already show high-end MVFR CIGs around 2.5-
3 kft. Meanwhile, high-resolution guidance is suggesting high
confidence for IFR/LIFR at KAST and KONP overnight with hourly
chances for IFR/LIFR CIGs around exceeding 60-70% at any hour
between 09-18z Fri. High pressure aloft isn`t strong enough to keep
marine layer really low. For now, the TAFs trend towards MVFR at
KAST and high-end IFR/MVFR at KONP, and will monitor how CIGs
progress overnight. Coastal terminals may also see VIS reductions to
IFR/MVFR tonight with the stratus.

Meanwhile, predominately VFR conditions with high clouds prevail for
Willamette Valley terminals throughout the TAF period. There is a 10-
15% chance for MVFR stratus across the Valley at any given hour
between 12-18z Fri, but confidence is too low to include in the
TAFs. Variable winds under 5 kt tonight across the region, becoming
more west/northwesterly 4-6 kt in the afternoon.

KPDX AND APPROACHES...VFR with high clouds and northwesterly winds 3-
5 kt through the TAF period. 10-15% chance for MVFR CIGs at any
given hour between 12-18z Fri.      -10

&&

.MARINE...Expect calmer weather today as a weak weather system
brushes the waters to the north. Winds will temporarily shift
out of the west around Cape Falcon northward this evening.
Northerly winds then return across the entire waters Friday
through the weekend into early next week, bringing wind gusts
around 10 to 20 knot. Otherwise, the west to northwesterly swell
of 4 to 6 ft at 9 to 11 seconds will gradually subside to around
3 to 5 ft at 8 to 9 seconds by Friday and persist through the
weekend. At this time, there are no other prominent swells of note
through at least the the middle of next week.   ~12

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

www.weather.gov/portland

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