742
FXUS66 KSEW 060001
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
401 PM PST Wed Feb 5 2025

.SYNOPSIS...An upper level low spinning offshore will bring snow
showers to western Washington through Thursday morning. Cold
temperatures will settle into the region Friday morning as the
trough shifts inland. A weak system will bring additional chances
of snow showers over the weekend, with cool temperatures and
periodic chances for more snow showers continuing into next week
as models favor moist northwest flow.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...A shortwave stemming from
an upper level low offshore will continue to move northward across
the region tonight, stirring up another round of intermittent snow
showers resulting in widespread accumulating snowfall this
afternoon into Thursday morning. With afternoon temperatures
currently in the mid 30s across much of the lowlands south of
Bellingham, precipitation has started off as a mixed bag with
reports of both snow and a rain/snow mix. As temperatures drop
into the evening, showers will transition to all snow. Due to the
convectively driven nature of these snow showers, snowfall amounts
will largely vary across the lowlands and will be dependent on
the strength of the showers that develop and the temperatures in
place where they develop. Confidence in the exact placement and
timing of heavier snowfall banding remains low, and forecast
models continue to struggle with this system. However, this round
of precipitation has the potential to bring more snowfall to the
lowlands than we have seen over the past several days, and nearly
all of the lowlands will likely see some snow on the ground by the
morning. The heaviest snow is favored to occur from Olympia to
Arlington, including the I-5 corridor, and over areas along the
Hood Canal, where accumulations will likely reach up to 2 inches
by the morning. Locally higher snow amounts will be possible in
any heavier precipitation or banding that develops, with some
forecast models showing potential for up to 4 inches of
accumulating snowfall where any heavier showers or banding occurs
overnight. Any snow that melted off this afternoon will re freeze
overnight as temperatures drop below freezing, causing slick spots
on untreated surfaces. A Winter Weather Advisory remains in effect
for most of the lowlands through Thursday morning, and San Juan
and western Whatcom Counties have been added to the Advisory. Snow
will taper off areawide Thursday morning as the upper low offshore
sinks southward and pulls the available moisture with it out of
the area.

Conditions will dry out across western Washington by Thursday
afternoon as the offshore low shifts southward. Clearing skies on
Thursday will bring significant cooling to the region overnight
into Friday morning, where most of the lowlands will see lows in
the teens to mid 20s. A Cold Weather Advisory has been issued for
cold conditions early Friday morning for the Cascade Foothills and
Puget Sound lowlands from King County northward to western Skagit
County. The Cold Weather Advisory for western Whatcom County has
also been extended through Friday, where Fraser River outflow
winds are weakening but still causing cold wind chills from
Bellingham northward.

Chances for additional snow showers increase again late Friday as
the upper low pushes inland to our south, with potential for some
wrap around moisture to generate more snow showers over western
Washington late Friday. A weak shortwave following close behind
could also bring in additional shower activity through Saturday
morning. However, at this time, confidence is low over the exact
placement and intensity of any showers that may develop.
Operational models favor moist northwest flow developing aloft for
the remainder of the weekend, which once again may trigger some
light snow showers across the region.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...Ensembles continue to
highlight more troughing heading into next week, maintaining
cooler temperatures and keeping a chance for additional shower
activity in the forecast. While a spread in the temperatures
forecast remains, highs are favored to stay below normal through
much of the long term.

15

&&

.AVIATION...A mix bag of ceilings and visibilities as scattered
rain/snow showers continue to move from south to north across
Western Washington. With temperatures decreasing below freezing
shortly after sunset, expect for the rain/snow mix to transition to
snow. It is difficult to pinpoint when and where the snow bands will
set up, as high-resolution guidance has had difficulty pinpointing
this event. Regardless, expect on and off snow shower activity to
last through Thursday morning. Expect reduced visibility and
ceilings (1-3 SM and IFR/LIFR) as the snow showers push through the
terminals. Ceilings expected to prevail overall at MVFR for the
majority of the terminals with pockets of IFR/LIFR ceilings near the
Kitsap Peninsula and southern Puget Sound. Improvement in ceilings
is expected after 21z-23z toward VFR.

Northeasterly winds still persisting at KBLI are expected to
gradually decrease to 6 to 10 kt by Wednesday night. As for the
other terminals, southerly flow with winds 5 to 8 kt. Winds will
shift northerly again after 15Z Thursday, with speeds of 4 to 8 kt .

.KSEA...Ceilings and visibility has been bouncing back and forth
between MVFR and VFR as scattered rain/snow showers move across the
terminal. Expect these showers to fully transition to snow after
sunset. Agreement on where and when the snow bands will set up has
been poor between the high-resolution guidance. However, expect on
and off snow showers to last through Thursday morning. Reduced
visibility down to 1-3 SM and periods of IFR/LIFR ceilings as the
snow showers pass over the terminal. Guidance hints at improvement
towards VFR after 15Z Thursday.

Southerly/southeasterly with winds 6 to 8 kt. Winds will shift more
northerly after 19Z on Thursday at 5 to 7 kt.

MGF

&&

.MARINE...A surface trough will slowly move inland through
Friday, followed by a weak shortwave trough over the weekend.
Light offshore flow will continue into early next week over area
waters, with combined seas staying fairly steady between 4 to 6
feet into early next week.

15

&&

.HYDROLOGY...No river flooding expected over the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 10 AM PST Thursday for Admiralty
     Inlet Area-Bellevue and Vicinity-Bremerton and Vicinity-
     Central Coast-East Puget Sound Lowlands-Eastern Strait of
     Juan de Fuca-Everett and Vicinity-Hood Canal Area-Lower
     Chehalis Valley Area-North Coast-San Juan County-Seattle
     and Vicinity-Southwest Interior-Tacoma Area-Western Skagit
     County-Western Strait of Juan De Fuca-Western Whatcom
     County.

     Cold Weather Advisory until 10 AM PST Friday for Western Whatcom
     County.

     Cold Weather Advisory from 10 PM Thursday to 10 AM PST Friday
     for Bellevue and Vicinity-East Puget Sound Lowlands-Everett
     and Vicinity-Seattle and Vicinity-Western Skagit County.

PZ...None.

&&

$$