869
FXUS66 KPQR 291012
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
312 AM PDT Tue Sep 29 2026

.SYNOPSIS...Today a decaying frontal system drops southward
clipping the region and bringing chances for rain through
tonight with the highest probabilities along the Washington and
north Oregon coast and Coast Range. Dry weather is favored
again by Wednesday, likely lasting through the weekend, with
temperatures trending warmer day to day as well.

&&

.DISCUSSION...Now through Monday night...Current radar and
satellite imagery early this morning shows precipitation/cloud
cover associated with a frontal system slowly sliding southward
into the region. As it progresses throughout the day it is
expected to continue weakening but there should be enough
lingering moisture to facilitate light rainfall over portions
of the Oregon coast and possibly the Portland Metro area and
locations northward into southwest Washington. The latest NBM
suggests there is still around a 45-60% chance for 0.25 inch of
rainfall from Tillamook northward, with a 50-60% chance for a
0.50 inch of rain or more in the Willapa Hills. Rain will be
more spotty with light amounts expected across portions of
southwest WA and the Portland metro, generally only 20-25%
chance for amounts to exceed 0.10 inch, while conditions Salem
southward remain mostly dry.

Thanks to the quick-hitting nature of this frontal system,
confidence is high widespread dry conditions return Wednesday
morning, and from this point onward dry weather likely
continues through the remainder of the week and weekend. The
one caveat includes a weak weather system potentially brushing
northern portions of our forecast area again on Thursday and
Thursday night. But in-line with prior weather model cycles,
most 00z ensemble members are keeping the rain pinned farther
north, with only 10% or less showing rainfall locally.
Temperatures remain fairly seasonable through the end of
September into the first couple of days of October with highs
generally in the low to mid 70s across the inland valleys.

By the weekend, models and their ensembles are in fairly good
agreement of a more pronounced ridge of high pressure building over
the region. This would maintain dry weather and potentially trend
afternoon temperatures around 5-10 degrees above normal for early
October. Clusters hint at more uncertainty though heading into early
next week as ensembles struggle to handle the potential breakdown
and progression of this upper-level ridge. -99/DH

&&

.AVIATION...Through 12Z Wednesday...Early this morning clouds
cover continues to increase across the region with MVFR
conditions along the coast while VFR CIGs/VIS prevail inland
though CIGs have been steadily dropping. For inland sites,
probabilities for terminals to experience MVFR conditions are
highest around the Portland metro at 50-70% between 16-21z. Low
clouds are likely more SCT to BKN throughout the central and
southern Willamette Valley with MVFR chances at 20-40% any
given hour between 14-21z. Southerly winds gradually increase
to 5-10 kt as a cold front associated with the trough moves
through the region. Higher speeds at KAST up to 10-15 kt with
gusts up to 20-25 kt expected.

KPDX AND APPROACHES...VFR conditions likely transition to MVFR
between 14-16z this morning due to lowering CIGs as a frontal
system enters the region. That said, we`ll likely see a switch
back to low-end VFR mid to late afternoon into the evening.
Expect southerly winds around 5-12 knots through the day. -99

&&

.MARINE...This morning a frontal boundary quickly approaches the
waters with southerly wind gusts in the 20-30 knot range peaking
north of Cape Falcon, especially right along the coastline. A
Small Craft Advisory remains in effect for coastal waters north
of Cape Foulweather, including the Columbia River Bar, into the
late afternoon and early evening hours. Behind the front, winds
are expected to abruptly shift to the northwest, transitioning to
a somewhat lighter northerly wind pattern Wednesday. Another weak
system may approach the northern waters from the west on
Thursday, but it likely holds north as it moves toward the
Washington coast then out of the region to the east. Northerly
winds then return Friday, likely persisting over the weekend.

A mid-period west-northwesterly swell of 6 to 8 ft at 13-15
seconds will move through the coastal waters today through tonight,
increasing significant wave heights into the 8 to 10 ft range.
Seas then gradually subside to around 4 to 6 ft later in the week
with no other prominent swells of note at this time. -99/DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ210.
     Small Craft Advisory until 5 PM PDT this afternoon for PZZ251-
     271.
     Small Craft Advisory from 5 AM early this morning to 5 PM PDT
     this afternoon for PZZ252-272.
&&

$$

www.weather.gov/portland

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