357
FXUS66 KSEW 210517
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
917 PM PST Thu Nov 20 2025

.SYNOPSIS...Drier weather through Friday morning as ridging
nudges into Western Washington. A stalled frontal system will be
located over British Columbia late Friday through Saturday. A
cold front will bring rain and higher elevation mountain
snowfall on Sunday. Cooler weather expected on Monday. Another
potential system may bring rain, mountain snow midweek.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...Generally dry
conditions this afternoon with a few lingering showers over the
Olympic Peninsula. Weak ridging will build into Western
Washington briefly into Friday morning for dry conditions
tonight. Some clearing, along with light winds, may promote fog
development, especially for the southern Puget Sound.
Temperatures tonight will cool into the mid 30s to low 40s, with
temperatures nearing freezing south of Olympia.

The aforementioned ridge will flatten for more westerly flow
aloft late Friday through Saturday as a frontal system stalls
over British Columbia. This will bring rain at times for the
northern Olympic Peninsula, as well as north interior (mainly
north of Snohomish County) Friday night through Saturday.
Conditions are expected to remain mainly dry south of Everett on
Saturday. South winds will also increase on Saturday, mainly
along the north coast and Whidbey Island northwards, with
localized gusts in these areas between 20 to 35 MPH.
Temperatures will be a few degrees warmer than normal on
Saturday in the mid 50s.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...The aforementioned
weather system over British Columbia will move through Western
Washington late Saturday through Sunday. Steadier rain is
expected on Sunday for the lowlands, as well as breezy winds,
with gusts ranging 20 to 35 MPH for most areas (locally higher
around Whidbey Island). Snow levels initially around 5500 feet
on Sunday will lower to 2500 feet by Sunday night. Snow will
increase for the Cascades during this period, with accumulating
snowfall expected for Snoqualmie and Stevens Pass Sunday night
into Monday. At this time, current snowfall forecast range 4 to
6 inches for the Passes, but a developing convergence zone
Sunday night may bring locally higher amounts in the vicinity of
the central Cascades. Precipitation slowly tapers off for the
Cascades on Monday.

Ensembles suggest a brief break in the precipitation Monday
night into early Tuesday with cooler temperatures. Heading into
midweek, there is indications in ensembles of a moisture plume
focused towards the Pacific Northwest. Variability remains in
individual ensemble members in the orientation of any potential
AR, thus uncertainty remains in QPF amounts and locations.
Looking at the Cluster Analysis for a 48 period ending 12z
Thursday, the multi-model ensemble mean (GEFS, EPS, GEPS) has
QPF amounts ranging 1-3" for the Olympics and Cascades.
Individual clusters show fluctuation in QPF amounts, with 55%
of the ensemble members showing over 3" of precipitation for
portions of the Cascades. Snow levels also remain uncertain by
midweek, but will also need to monitor the potential for snow
over the higher elevation Cascade Passes. If you`re traveling
next week, continue to monitor the forecasts. JD

&&

.AVIATION...Westerly flow aloft with flat upper level ridge over
the area. Weak system, moving by mostly to the north Friday
afternoon into Saturday morning. Light flow in the lower levels.

VFR ceilings into Friday afternoon. Local low clouds and fog
reducing ceilings below 200 feet and visibilities 1/2 a mile or
less until 16z mainly over the Kitsap Peninsula and South Puget
Sound. MVFR ceilings near the Strait of Juan de Fuca through 16z
as well.

KSEA...Tough call for the morning at the terminal. Temperature
dew point spread 5 degrees at 05z/9 pm. Southeast surface winds
overnight weakening Friday morning. Question is will they weaken
enough to allow fog to form. Right now looks like it will but
close enough call to put a lower scattered stratus layer with
some reduced visibility in the 13z-18z window. VFR conditions
until the possible low cloud development and afterwards Friday
afternoon. Southeasterly wind 4 to 8 knots making its way around
to southwesterly by Friday afternoon. Felton

&&

.MARINE...Large waves will continue building over the coastal
waters, western Strait, and Grays Harbor bar , peaking this
evening at 13-17 ft. A Small Craft Advisory remains in effect
for these areas. Waves will gradually decrease overnight into
Friday, but will hover around 9-11 ft. A weather system will
traverse area waters this weekend, bringing the potential for
small craft winds to area waters. Latest guidance suggests the
central Strait has the highest chance (30-45%) of sustained
speeds meeting criteria Sunday afternoon/evening into early
Monday morning. There is also the potential for gale gusts along
the central Strait, with latest guidance at 25-35%.

29

&&

.HYDROLOGY...A weather system will move across Western
Washington late Saturday into Monday for lowland rain and
mountain snowfall. No river flooding is expected during this
period, but rivers will rise. The potential exists for
additional, heavier precipitation during the middle of next
week. However, uncertainty exists in both the location and
duration of precipitation. River levels will continue to be
monitored during this mid to late week period. JD

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until noon PST Friday for Grays Harbor
     Bar.

     Small Craft Advisory until 4 AM PST Friday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From Cape Flattery To James Island Out 10 Nm-
     Coastal Waters From James Island To Point Grenville 10 To
     60 Nm-Coastal Waters From James Island To Point Grenville
     Out 10 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm-Coastal Waters From Point
     Grenville To Cape Shoalwater Out 10 Nm-West Entrance U.S.
     Waters Strait Of Juan De Fuca.

&&

$$