057
FXUS66 KPQR 051135
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
435 AM PDT Mon Oct 5 2026

Updated aviation discussion.

&&

.SYNOPSIS...Unseasonably warm and dry conditions continue
through Thursday with areas of early morning valley and coastal
fog. Weak offshore flow will see slightly warmer temperatures
midweek, before a trough brings a return to cooler temperatures
with chances for light rain Friday into the weekend.

&&

.SHORT TERM...Now through Thursday Night...Low amplitude upper
ridging will persist overhead through midweek, leading to
continued unseasonably warm and dry weather. Afternoon highs
inland will continue to reach about 10 degrees above normal for
early October each of Tuesday and Wednesday afternoons. Nightly
fog or low clouds will also reoccur along the coast and within
inland valleys, however the relatively weaker ridge aloft will
yield a deeper surface layer and likely lesser impacts to the
visibility at the surface. Much of the coast, southern and
central Willamette Valley, eastern Portland/Vancouver metro
area, and lower Columbia and Cowlitz Valleys will see 30-60%
chances of visibility less than 1/2 mile through 8-9 AM PDT this
morning; if observed visibility falls below 1/4 mile, Dense Fog
Advisories may be needed. Morning commuters may encounter
limited visibility on area roadways and should consider allowing
for extra time.

By Wednesday and Thursday, upper-level ridging will re-amplify
over the West Coast, pushing mid-level temperatures back up near
20C and allowing a weak coastal thermal trough to develop. This
will again yield an offshore pressure gradient which will drive
easterly flow, however the magnitude of the gradient remains
uncertain. Mid-range ensembles support a mean value near -2 mb
between Portland and The Dalles, similar in magnitude to this
past weekend when nocturnal east winds developed in the Cascades
and foothills with gusts as high as 20-30 mph in the western
Columbia Gorge and nearby terrain. Warm temperatures in the
upper 70s to low 80s are also expected Wednesday and especially
Thursday afternoon, some 10-15 degrees above normal. Despite
this abnormal warmth, daily records on Thursday in the upper 80s
at northern Willamette Valley sites (Portland, Vancouver,
Hillsboro, McMinnville) will likely be out of reach. However,
daily records at Salem (84F set in 1971 and 2022) and Eugene
(83F set in 1934 and 1943) may be in jeopardy. -36


.LONG TERM...Friday through Sunday...Late in the week and into
this weekend, long-range ensemble guidance supports an upper-
level trough developing over the Pacific Northwest, bringing a
return to onshore flow, cooler and more seasonable temperatures,
and low chances for light rain. While there continues to be
uncertainty in its evolution, the majority of ensemble members
still maintain light rain arriving along the north Oregon and
south Washington coast around midday Friday, reaching inland
areas by Friday afternoon. Potential rainfall amounts continue
to look very light, with a 10% or less chance for even 0.1
inches of rain for most.

As the core of the upper trough moves overhead, much cooler air
aloft will allow for sharply cooler low temperatures Saturday
and especially Sunday morning. Chances for temperatures in the
mid 30s supporting frost will reach 25-35% in the Upper Hood
River Valley around Parkdale and Dee on Saturday morning,
increasing to 35-65% and including lower elevations near Odell
on Sunday morning, as well as near 10% in Hood River proper.
Chances for frost will also reach 30-50% in north Oregon Coast
Range valleys, 15-30% in the southern Willamette Valley and
Cascade foothills from Cowlitz County south to Lane County, and
5-10% in the central Willamette Valley on Sunday. Chances for a
true freeze Sunday morning are limited to 25-35% in the Upper
Hood River Valley near Parkdale and Dee, and 5-10% along OR-58
between Eugene and Oakridge. Those with agricultural interests
or home growers with sensitive outdoor plants should continue to
monitor the forecast this week. -36

&&

.AVIATION...Through 12z Tuesday...Latest terminal observations
again show areas of IFR/LIFR cigs/vis as low clouds or areas of
fog/mist reoccur early this morning. Coastal terminals are
largely seeing LIFR conditions, although satellite imagery shows
clearing only 10 miles or so offshore off the north OR and
south WA coasts, meaning KAST/KTMK and other small terminals may
see improved conditions earlier if nearshore clouds break up.
Farther south along the central OR coast, the low cloud deck is
more solid, leading to higher confidence in persistent LIFR
condition this morning. As diurnal northwest winds increase to
10-15 kt with gusts of 20-25 kt after 17-19z Mon, mechanical
mixing will help lift and break up low clouds, with a period of
VFR conditions favored after 20-21z Mon. Winds ease and low
clouds bringing vis/cig restrictions return this evening by
00-03z Tue.

At inland terminals, areas of fog/mist are also beginning to
develop in favored locations, notably including the southern
Willamette Valley and lower Columbia/Cowlitz Valleys where
largely LIFR conditions prevail. Elsewhere, VFR conditions
remain in place, but chances for IFR vis will increase to 30-60%
in the hours around sunrise; TEMPO groups in TAFs at all
terminals reflect the chances for intermittent MVFR/IFR vis as
local pockets of fog develop through 16-17z Mon, after which
daytime heating and diurnal north to northwest winds rising to
5-10 kt will clear any remaining low clouds.

KPDX AND APPROACHES...VFR conditions most likely to prevail
throughout the period. Chances for fog/mist to produce IFR vis
restrictions increases to 40% from 14-17z Mon, after which
there is high confidence in a return to VFR as daytime heating
and northwest winds rising to 5-8 kt aid in mixing out any
remaining clouds. -36

&&

.MARINE...
High pressure offshore will continue to maintain
diurnal northerly winds through the week with peak afternoon
and evening wind gusts of 20-25 kt today through Wednesday.
Small Craft Advisories remain in effect from 11 AM until 11 PM
PDT today within 10 NM south of Cape Falcon and out to 60 NM
south of Cape Foulweather. Expect largely wind-driven seas
around 4-6 ft through midweek, with a west-northwest swell of
3-4 ft at 10-12 seconds.

High pressure aloft will also support areas of dense fog
developing nightly as cloud bases are compressed down to the
surface. Dense Fog Advisories for widespread visibility of 1 SM
or less also remain in effect across the coastal waters
including the Columbia River Bar until noon PDT today.

More active marine conditions are likely in the latter half of
the week as troughing over the Gulf of Alaska generates a
building northwest swell and chances for rain return to the
region Friday into the weekend. Seas will increase to 7-10 ft
Wednesday into Thursday, with the longer-period swell also
supporting a moderate risk for sneaker waves to the coast. -36

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Dense Fog Advisory until noon PDT today for PZZ210-251>253-
     271>273.
     Small Craft Advisory from 11 AM this morning to 11 PM PDT this
     evening for PZZ252-253-273.
&&

$$

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