260
FXUS66 KSEW 100313
AFDSEW

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

.SYNOPSIS...An upper level low offshore will lead to cool and
unsettled conditions into the weekend. Another trough dropping
southward from British Columbia early in the coming week will likely
produce the first noteworthy high elevation snow of the season.
Drier conditions will prevail toward the middle of next week as high
pressure aloft rebuilds into the region.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...A quick update was
made to the forecast this evening for the overnight hours to include
the correct precip type. An upper level low churning offshore is
clipping the far southwest corner of the CWA with scattered showers
and isolated thunderstorms. Overall precip coverage is expected to
increase toward early Friday morning as the next upper disturbance
rotates northward into the area. The remainder of the forecast is
unchanged for now. The previous forecast discussion follows with
updates to marine and aviation portions. 27

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 will persist aloft with an upper level
low offshore tonight, before shifting more southeasterly Friday
morning. Surface winds generally persisting out of the north between
5-10 kts tonight, but will become light again during the overnight
period and shift to the south/southeast.

VFR conditions remain in place across the majority of W WA this
evening with most terminals seeing only some mid to high level
clouds. Radar does show some showers and isolated thunderstorms
moving up along the coast from OR, however, so could see some
reductions in cigs and vis at KHQM over the next few hours. As the
upper level low shifts eastward tonight, will see better chances for
additional shower development overnight. Expect cigs to lower down
into more uniform MVFR conditions across the area by Friday morning,
with these conditions expected to carry over into the late afternoon
hours.

KSEA...VFR conditions through tonight and a majority of the
overnight period. As shower activity becomes more consistent by
early Friday morning, will see cigs fall to MVFR /between 1500- 2000
ft/ around 12Z. Expect MVFR cigs to persist through the afternoon
hours, before seeing improvement back to VFR. Winds out of the north
between 5-10 kt tonight. Winds will ease to 6 kt or less and shift
to the south/southeast during the overnight period.

18/14

&&

.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 are 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 3 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.

&&

$$