378
FXUS66 KPQR 032148
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
248 PM PDT Fri Oct 3 2025

.SYNOPSIS...40-70% chance of light rain showers Friday night into
early Saturday morning. Showers should become more isolated Saturday
afternoon. Low-level offshore flow develops Sunday and continues
through at least Tuesday, bringing an extended period of dry weather
with breezy east to northeast winds and daytime high temperatures in
the 70s across the lowlands.

&&

.DISCUSSION...Friday night through Thursday night...Water vapor
imagery from early Friday afternoon depicted a swath of enhanced
moisture over Vancouver Island and the adjacent coastal waters,
moving southeastward towards northwestern Washington. This area of
moisture is evident along and ahead of a weak upper level shortwave
trough. The latest suite of model guidance continues to suggest this
shortwave trough will move southeastward across western WA and
northwest OR late Friday night into early Saturday morning, bringing
increasing chances for light rain showers to the area. It appears
there will be a break in showers mid to late Saturday morning, before
diurnally driven showers redevelop Saturday afternoon. That said,
hi-res model guidance suggests showers will be quite isolated and
light. Forecast soundings depict very shallow convection with low
equilibrium levels. As such, much of the day will be dry on Saturday,
and most locations will only observe a trace of rain to a few
hundredths of an inch. Expect seasonable temperatures with afternoon
highs in the 60s.

The weather pattern begins to change on Sunday as a thermally induced
surface trough begins building northward into northwest Oregon while
surface high pressure develops east of the Cascades. This will bring
a transition to low-level offshore flow, with east to northeast winds
becoming rather breezy at times, especially on exposed ridgetops in
the Cascades. The Columbia River Gorge and Willamette Valley will
also be breezy. Winds are not expected to be strong enough for wind
damage or notable impacts to occur. The offshore flow pattern looks
to stay in place through at least Tuesday, resulting in at least
three consecutive days with dry/breezy/sunny conditions. Temperatures
will also become noticeably warmer with highs in the 70s across the
lowlands. Tuesday is still shaping up to be the warmest day of the
week with highs in the mid to upper 70s, except lower 70s at the
coast.

Chances for rain return to the forecast late Wednesday into Thursday,
however uncertainty is high that far out in time. While the LREF
grand ensemble mean shows rain amounts ranging between 0.1-0.2 inches
during that time, overall model spread is very large. For example,
the LREF 10-25th percentile for QPF shows no rain at all, while the
90th percentile shows 0.4-0.6 inches. The outcome will also impact
temperatures. If conditions remain dry and mostly sunny, high temps
will likely stay in the 70s. If conditions wind up cloudy and wet,
highs will cool into the 60s. Currently the warmer/drier solution is
favored over the cool/wet solution based on LREF and NBM
probabilistic guidance, albeit not by much. -59

&&

.AVIATION...Satellite imagery as of Friday afternoon depicts
clearing skies and scattered clouds as much of the morning stratus
has now broken out. Most terminals are now predominately VFR,
except for LIFR conditions at KONP. Tonight, a weak shortwave
trough will brush the region, returning lower CIGs and scattered
showers. High confidence (60-80% chance) that IFR/MVFR CIGs or
lower return along the coast by 02-04z Sat, with moderate
confidence (40-70% chance) across Valley terminals after 09-12z
Sat. The highest chances for MVFR CIGs in the Valley are around
the Portland/Vancouver Metro Area. It looks like onshore flow will
favor stratus developing along the Cascade foothills and back-
building into the Valley. Winds generally west-southwesterly under
5 kt across the area, becoming variable and under 5 kt overnight.

KPDX AND APPROACHES...VFR conditions with mid to high level
clouds prevail through this evening. CIGs lower as a weak system
moves through, bringing a 50-70% chance for MVFR CIGs returning
around 09-12z Sat. Southwesterly winds this evening around 5 kt,
becoming variable under 5 kt overnight. -10

&&

.MARINE...A very weak low pressure system will maintain southerly
to southwesterly winds across all waters through this evening.
Since pressure gradients don`t look too tight with this system,
winds remain around 5-10 kt with gusts up to 15 kt tonight
(strongest over the central and southern outer waters). Despite
winds being around 15 kt or less, seas will remain choppy. A brief
Small Craft Advisory has been issued from 11 PM Fri to 5 AM Sat
for choppy seas beyond 10 NM south of Cape Falcon. Expect 6-7 ft
seas at 8-9 seconds through Saturday morning.

Winds shift northwesterly early Saturday morning as surface high
pressure re-builds following the weak system. Northwesterly winds
remain under 15 kt on Saturday, however, stronger high pressure
and tightening pressure gradients will make winds breezier on
Sunday. Winds also shift more northeasterly Sunday into early
next week as a thermal trough develops along the coast. Guidance
suggests high confidence (60-80% chance) that the waters beyond 10
NM south of Cape Falcon will experience northeasterly wind gusts
up to 25 kt (small craft conditions) on Sunday. Elsewhere, these
chances remain around 20% or less. Seas fall to 4-6 ft on
Saturday, and hold through early next week. -10

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 11 PM this evening to 5 AM PDT
     Saturday for PZZ272-273.
&&

$$

www.weather.gov/portland

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