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FXUS66 KSEW 212322
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
322 PM PST Tue Jan 21 2025

.SYNOPSIS...Increased cloud cover late Tuesday afternoon as a
weak system moves through Western Washington. Upper level ridging
rebuilds Tuesday night bringing drier conditions through Thursday
evening. A weak system on Friday will bring mountain snow to the
Cascades. Riding will rebuild offshore Friday night bringing drier
conditions through next Tuesday.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...Satellite imagery shows
mostly clear skies across most of Western Washington this
afternoon. Increased cloud cover (mostly along the northern
coast, Puget Sound, and northern interior) is expected later
this afternoon as a shortwave trough digs southward. No additional
precipitation is expected with this system. Upper level ridging
will rebuild offshore Tuesday night as the shortwave moves
eastward. Minimal cloud coverage Tuesday night into Wednesday
morning and light winds will promote the formation of patchy fog
over the southern interior. Expect the fog to begin lifting
shortly after sunrise. High temperatures will be in the 40s and
low temperatures will be in the upper 20s to low 30s on Wednesday.
Another round of patchy fog is likely Wednesday night into
Thursday morning along the southern interior.

The upper level ridge offshore shifts slightly westward by
Thursday, allowing an upper level trough to move into Western
Washington late Thursday night into Friday. The northern and
central Cascades will see the highest chance (45%-55% probability)
of snow on Thursday night, while the southern Cascades will see a
slightly lower chance (30%-40%) of snow on Friday morning as the
upper level trough pushes southward. No significant impacts are
expected with this system, with snow accumulations of generally an
inch or less. Away from the mountains, expect to see an increase
in cloud cover as the system pushes through the area. Upper level
ridging will rebuild offshore on Friday night.

.LONG TERM /SATURDAY THROUGH TUESDAY/...There is generally good
agreement between ensemble clusters that an amplified upper level
ridge offshore will be the dominant feature through Tuesday,
keeping Western Washington dry. Expect mostly clear skies and calm
winds through this period. High temperatures will be in the 40s.
Cold overnight temperatures are expected to persist through this
period. Low temperatures will be in the mid to upper 20s.

Although amplified ridging is favored on Tuesday by the majority
of ensemble members (70%), some solutions do begin to differ
slightly from the favored solution. One of the solutions (16% of
members) hint at moderate broad ridging over the Western CONUS,
while another solution (13% of members) has the ridge weakening
and zonal flow establishing over the Pacific Northwest.

MGF

&&

.AVIATION...Northwesterly flow aloft as high pressure continues to
dominate over western Washington. VFR conditions at all area
terminals this afternoon with a mix of some high level clouds
streaming over the region. High clouds will continue to stream in
tonight which will likely limit the development of area wide fog,
although, isolated freezing fog will be possible in the Southwest
Interior and typical locations near the Chehalis valley for a mix
of IFR/LIFR conditions early Wednesday morning. Elsewhere, can
expect VFR to prevail for the remaining of the TAF period.

KSEA...VFR conditions this afternoon with some high clouds
overhead. Light and variable winds will slowly turn N/NE and
remain around 3 to 6 knots overnight. Latest guidance is not
confident in fog developing early Wednesday morning especially
with the high clouds around (30% chance of IFR/LIFR conditions
around 09z-12z). VFR will likely continue throughout the TAF
period.

Mazurkiewicz

&&

.MARINE...High pressure will continue to remain over the waters
for generally benign conditions. A weak front looks to cross over
the area waters Thursday night which will bring some Small Craft
Advisory winds over the outer coastal waters. Winds will continue
to remain north to northeasterly over the waters through this
weekend as weak Fraser outflow winds develop.

Seas 6 to 8 feet this afternoon will gradually decrease to around
3 to 6 feet into Wednesday. Seas will then slowly build up to 8 to
12 feet across the coastal waters on Friday, subsiding to 3 to 6
feet over the weekend.

Mazurkiewicz

&&

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

&&

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

$$

NWS SEW Office Area Forecast Discussion