657
FXUS66 KPQR 020547 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
947 PM PST Sun Nov 1 2026

Updated Aviation Discussion...

.SYNOPSIS...The region remains under the influence of a ridge of
high pressure through Monday with additional low clouds/fog and
limited clearing across the inland valleys. Clearer skies above
the inversion in the Coast Range/Cascades, and along the coast.
Mostly dry conditions likely persist through Tuesday as a weak
frontal boundary grazes the coast. Then, an active and wetter
weather pattern returns the second half of Wednesday through the
rest of the week.

&&

.DISCUSSION...Now Through Saturday...This afternoon satellite
imagery continues to show prolific low stratus across the
interior valleys as a strong temperature inversion and weaker
November sun-angle/insolation struggle to facilitate any
appreciable clearing along the I-5 corridor. Those along the
coast and above roughly ~1000-2000ft will continue to enjoy
sunny conditions into the evening. As the axis of the upper-
level ridge passes overhead tonight, the temperature inversion
will strengthen further with continued low stratus and fog into
Monday morning across the lower elevations. Once again, clearing
may be a struggle across the interior lowlands Monday
afternoon, presenting the biggest point of forecast uncertainty
in the short term. Even the higher resolution models like the
HRRR/UW-WRF/REFS/HREF/etc., notoriously struggle in these
scenarios and almost always over-mix the boundary layer
resulting in more clearing than actually occurs. Today (Sunday)
was a great example of this. Should we clear out (unlikely) high
temperatures would jump into the mid to upper 50s, however if
low clouds remained pinned over the Willamette Valley and SW
Washington, highs only rise into the 40s. Nonetheless, most of
our impacts during this time period revolve around fog which
will reduce visibility wherever present.

Then late Monday into Tuesday the latest model ensemble
guidance is in good agreement showing a low pressure system
off the northern California coast moving straight east,
remaining south of the forecast area. While there is still a
slight chance (10-15%) a weak frontal boundary on the northern
periphery of the low is able to squeeze out some light rain
along the north Oregon coast, the vast majority of western
Oregon and southwest Washington should remain dry. At least the
weak troughing overhead and cooling temperatures in the mid-
levels by Tuesday afternoon should weaken the temperature
inversion and help our daytime lingering low cloud/fog
situation. It`s also worth quickly noting the placement of this
low pressure system likely facilitates a period of locally
breezy/gusty east winds through the Cascade gaps and western
Columbia River Gorge, peaking Tuesday morning.

Behind this weather system passing to our south, a shortwave
trough quickly pushes a frontal system toward the coast later
Wednesday, increasing precipitation chances across the area
through Wed night. Most ensembles indicate this system will be
weakening with just light amounts of rainfall most likely -
generally 0.1-0.30" coast range/Cascades, <0.10" inland valleys.
Cluster analysis of 500 mb heights are in relatively good
agreement heading into the latter part of the week with zonal to
southwest flow aloft allowing for a somewhat active pattern
over the NE Pacific to approach the coast. There is still quite
a bit of uncertainty in regards to exact rainfall coverage and
amounts, but there is continued potential for multiple rounds
of systems moving across the area into next weekend. At this
point, no significant precipitation impacts are expected with
any of these weather systems, and snow levels hold around
5000-6000ft. -99/DH

&&

.AVIATION...Through 06Z Tuesday...Current satellite shows low
stratus across the interior lowlands, imposing MVFR to IFR CIGs
across inland terminals as of 05Z Mon. Expect this low stratus to
gradually lower overnight, bringing a 50-70% chance of LIFR fog
between 09-18Z Mon. Similar to last night, the terminal with the
least confidence for fog is KTTD, especially with easterly winds
expected to increase around the terminal by 16Z Mon. By 19-21Z
Mon, expect all terminals to improve back to VFR. While
probabilistic guidance does not suggest lingering deteriorated
conditions beyond 18Z Mon, mid to high level clouds which will
move over the airspace tonight could prevent the sun from
scouring out the low stratus in the morning. Coastal terminals
will likely remain VFR through the TAF period, with probabilistic
guidance only suggesting a 10-15% chance of LIFR and 15-20% chance
of MVFR CIGs between 09-18Z Mon. Winds remain generally light and
variable through the TAF period, although more northerly inland
and easterly along the coast.

KPDX AND APPROACHES...Current MVFR CIGs will lower overnight,
possibly becoming LIFR fog by 10-11Z Mon. Expect conditions to
improve back to VFR by 18-19Z Mon. Mid to high clouds aloft may
inhibit the sun from scouring out the low stratus in the morning,
although confidence is low given little support from guidance.
Variable winds under 4 kt through most of the period, becoming
easterly around 5 kt by the afternoon. ~12

&&

.MARINE...Benign conditions are expected across the coastal
waters through this evening as high pressure returns. Winds
remain light below 10 kt. Light offshore winds develop late
tonight and persist into early next week. Seas remain around 3 to
4 ft this afternoon, but an incoming long period west-northwest
swell is expected to build seas starting this evening. Seas build
to around 8 to 11 ft at 15-19 seconds Monday morning. Small Craft
Advisories remain in effect for the outer coastal waters beyond 10
NM offshore for wave heights peaking at around 10 to 11 ft
through Tuesday morning. This long period swell will result in a
moderate threat for sneaker waves at the coast Sunday evening
through Tuesday. Caution should be used at beaches when in or near
the water.

A weak frontal system approaches the waters on Wednesday,
returning increasing southerly winds. By the end of the week,
model guidance hints at a stronger system entering the waters,
resulting in a 60-80% chance for maximum wind gusts exceeding 21
kt on Friday. In addition, a steeper, longer period swell will
build seas into the mid teens with a 15-20% chance for seas
exceeding 20 ft.       -10/DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Dense Fog Advisory from 1 AM to 10 AM PST Monday for ORZ104-105-
     108-109-111-112-114>118.

WA...Dense Fog Advisory from 1 AM to 10 AM PST Monday for WAZ204>207.

PZ...Small Craft Advisory from 7 AM Monday to 7 AM PST Tuesday for
     PZZ271>273.
&&

$$

www.weather.gov/portland

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