056
FXUS66 KSEW 092201
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
301 PM PDT Thu Oct 9 2025

.SYNOPSIS...An approaching, offshore upper level low will set
the stage for a pattern shift to cooler and wetter weather
through the weekend and into early next week. In addition to
widespread rain there will be periods of breezy conditions, and
lowering snow levels Saturday night into early next week that
will result in the first notable high elevation snow of the
season.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...The offshore
upper level low lingering along 130W will begin to shift onshore
Friday afternoon and evening. Light precipitation associated
with this system may begin to trickle into into southwestern
Washington this evening, and more earnestly Friday morning with
widespread stratiform rain setting up over most of the region by
Friday afternoon and lingering through Saturday. As the upper
level low begins to shift onshore into Oregon Friday evening
there may be enough marginal support for isolated thunderstorms
mainly along the coast and possibly over the higher terrain.
Gusty southerly winds particularly early Saturday morning near
Whidbey Island to western Whatcom county are possible.
Temperatures will remain near normal Friday, trending cooler
with highs over the lowlands in the mid to upper 50s Saturday.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...Another surge of
widespread precipitation is expected Early Sunday morning as an
upper level trough slides southward through British Columbia.
In addition to precipitation, this will bring a surge of cooler
air and much lower snow levels, now expected dip to around 3000
feet in the northern Cascades to 4000 ft in the southern
Cascades by Monday morning. This will opening the door the first
notable high elevation snowfall for the higher elevations. Best
bets for accumulations are above 5000 feet, with an 80% chance
of 2 or more inches at Rainy Pass, and a 45% chance at Stevens
Pass. Accumulations are not expected at Snoqualmie pass, however
there is a good chance for periods of mixed rain and snow
particularly in the early morning hours Sunday and again Monday
morning. For those that plan to head to the higher mountain
elevations this weekend should be prepared to encounter snow and
cold conditions and closely monitor the weather forecast in the
next few days.

Ensemble guidance into the medium range continues to favor the
upper low digging south into California early next week, pulling
precipitation with it resulting in a drier trend. It will also
help support the potential for cool, clear nights and the
potential for frost in the mornings as low temperatures trend
closer to the 30s for some locations in the interior away from
the water.

&&

.AVIATION...Southerly flow aloft with an upper level low offshore
today, shifting southeasterly Friday morning. Surface winds
remaining light and variable a little later than expected for most
terminals, but still expected to become northerly 4-8 kts by 00Z
late this afternoon and continue this evening. Light and variable
winds will return overnight tonight.

VFR conditions remain in place over the bulk of W WA this afternoon
with most terminals seeing only mid to high level clouds at the time
of this writing /22Z/. CLM is the only exception, where lingering
stratus is resulting in continued MVFR conditions there. Model
guidance continues to suggest they should break out and become VFR
by 00Z...but with how long these stratus has lingered, confidence in
this solution is shaken. May opt to keep the lower cigs in for the
00Z update. As the upper level low shifts eastward tonight, will see
better chances for showers overnight with cigs lowering down into
more uniform MVFR conditions throughout the area carrying over into
the remainder of the TAF period.

KSEA...VFR conditions through tonight and a majority of the
overnight period. As showers become more consistent by very early
Friday morning, will see cigs fall to MVFR /around 2000 ft/ between
09-12Z remaining there for the rest of the TAF period. Surface wind
discussion from above applies, with SEA expected to be on the higher
end of the range of wind speeds after 00Z. Additionally, winds
overnight will be more southerly with speeds around 5 kts.

18

&&

.MARINE...The offshore low pressure system will to linger over
the offshore waters of Oregon into Friday then move inland
Friday into Saturday. Winds and seas will increase on Saturday
as strengthening high pressure across the NE Pacific pushes in
quickly behind the low. Winds look to reach high-end SCA
criteria across the coastal waters with 40-70% chances for gale
force gusts through Sunday morning. Seas above 10 feet will also
begin to move into the outer coastal waters with steep seas
possible. Winds area also expected to increase through the
Strait of Juan de Fuca as well. Another low pressure system
looks to move into the coastal waters Sunday night into Monday.
This will allow winds to become offshore, with winds requiring
additional headlines possible through the Strait, with a 70%
chance of gusts at or above 34 kts on Monday in the central
Strait.

Seas 4 to 6 ft tonight will linger into Friday then build
Saturday to 12 to 16 ft over the weekend. Seas then look to ease
Sunday, becoming 6 to 8 ft for the first part of next week.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...None.

&&

$$