580
FXUS66 KSEW 231735
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
935 AM PST Thu Jan 23 2025


.UPDATE...No changes made to the inherited forecast. The previous
discussion remains below along with an updated aviation section.


&&

.SYNOPSIS...Upper level ridge over the area weakening and shifting
west today. Weak system moving down British Columbia coast moving
through tonight. Ridge rebuilding offshore Friday with the ridge
nosing into British Columbia over the weekend. The ridge will move
directly over Western Washington Monday and Tuesday then weaken
and shift west again Wednesday. This will open the door to
possible weather systems the latter half of next week.

&&

.SHORT TERM /TODAY THROUGH SATURDAY/...Satellite imagery shows
just a few high clouds over Western Washington early this morning.
Stratus once again in the Strait of Georgia but unlike yesterday
morning the stratus is not spilling south into the San Juans.
Patchy freezing fog around Arlington and Olympia. Temperatures in
the mid 20s to lower 30s.

Upper level ridge over the area this morning weakening and
shifting west this afternoon. Shortwave currently located near
Haida Gwaii will move south during the day but still over Southern
British Columbia by late afternoon. Clouds increasing from the
north this afternoon with just a slight chance of showers near the
Canadian border late this afternoon. Highs in the lower to mid
40s.

Shortwave moving through Western Washington overnight. Not much
left of this feature by the time it moves over the area making for
a chance pops at best forecast. Cloud cover will keep temperatures
just above freezing overnight in most locations. Temperatures
dropping just below freezing in Whatcom county early Friday
morning but by that point the moisture is pretty much gone. Lows
tonight in the mid 30s.

Shortwave south of the area Friday. Upper level ridge offshore
strengthening. Increasing dry northerly flow aloft clearing skies
out across the area early in the day. Even with plenty of
afternoon sunshine highs will again be below normal, in the lower
to mid 40s.

Upper level ridge continuing to build Friday night into Saturday
with the ridge nosing into British Columbia. Dry north
northeasterly flow aloft. Light gradients at the surface for
another round of patchy freezing fog early Saturday morning in
the usual locations like the Southwest Interior. Lows mid 20s to
lower 30s. Highs lower to mid 40s.

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...Extended models showing
good consistency both run to run and with each other. Upper level
rex block pattern, upper level ridge over us and to the north with
upper level low over Central and Southern California setting up
Saturday night. This is a very stable pattern and it will remain
in place into Tuesday. Pattern breaking down Wednesday with upper
level low kicking out to the east and the upper level ridge over
Western Washington weakening. Wednesday still a dry day but
changes are in the offing for later next week. In the meantime, more
of the same through the extended period with sunny days and clear
nights. Patchy freezing fog each morning. Highs lower to mid 40s.
Lows in the 20s to lower 30s. Felton

&&

.AVIATION...Northwest flow aloft continues today as an upper level
ridge remains in place. A shortwave trough will dampen the ridge as
it moves through over the area late tonight. VFR conditions with
high clouds remain across the northeastern portions of the area,
otherwise clear skies prevail. Fog was a bit slow to develop this
morning, but satellite imagery now shows freezing fog has formed
along South Puget Sound and is slowly filling in south toward OLM
and Southwest Interior. Any fog that develops this morning should
burn off fairly quickly as mid to high level cloud cover increases
this afternoon ahead of an incoming frontal system. This front will
work its way from north to south across the area, lowering ceilings
to MFVR as it does so this evening into tonight. Little to no
precipitation is expected with this system.

Light to calm winds this morning, and not expected to increase much
today until after the front moves through this evening, but expect
winds to remain north/northwesterly today.

KSEA...VFR conditions prevail early this morning. With slower onset
of fog across the Southwest Interior, will condense the time concern
of fog development at the terminal, but overall less confident in
the potential for seeing fog at the terminal altogether this
morning. Any fog that reaches should dissipate fairly quickly before
high cloud cover returns later this morning. CIGs lower to MVFR this
evening as a dry and weak front passes through the area from the
north. Northeast winds continue this morning and expected to remain
that way through the morning. Winds may briefly turn southerly ahead
of the front this afternoon before returning to northeasterly this
evening.

62/MGF

&&

.MARINE... Broad high pressure will weaken throughout the day today
as a weak frontal system moves southward from British Columbia
tonight into early Friday. Northerly winds will pick up this evening
with the strongest winds expected over the outermost coastal waters,
for which a Small Craft Advisory has been issued through early
Friday morning. High pressure will rebuild over interior British
Columbia late Friday into the weekend with a surface trough along
the coast, allowing for weak Fraser outflow to develop along with
offshore flow across the coastal waters. This pattern look to
continue into early next week with the next system not arriving
until the latter half of next week.

Seas 3 to 5 ft early this morning will build to 8 to 12 ft tonight
into Friday then subsiding back to around 4 to 6 ft this weekend and
into next week.

62

&&

.HYDROLOGY...


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from 4 PM this afternoon to 4 PM PST Friday
     for Coastal Waters From Cape Flattery To James Island 10 To
     60 Nm-Coastal Waters From James Island To Point Grenville
     10 To 60 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater 10 To 60 Nm.

&&

$$