Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 242250
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
250 PM PST Sat Feb 24 2024

.SYNOPSIS...The first of several weather systems arrives tonight
into Sunday with heavy mountain snow, lowland rain, and locally
windy conditions developing. Snow levels will drop below 1000 feet
behind the front Sunday night into Monday. Another strong front
arrives on Wednesday with cool and unsettled conditions to follow
through the end of the coming week.


&&

.SHORT TERM /TODAY THROUGH MONDAY/...Overcast skies and spotty
light precipitation continues across Western Washington this
afternoon ahead of a warm front that will shift onshore over
southern British Columbia this evening. Precipitation coverage
will increase later tonight into Sunday morning ahead of a
vigorous cold front that will sweep across the region Sunday
afternoon. Strong west to northwest flow aloft will limit the QPF
around much of central Puget Sound via some shadowing by the
Olympics. But that same strong westerly flow will be a prolific
snow producer in the Cascades with 850 millibar winds approaching
45 knots by Sunday afternoon. Strong post-frontal onshore flow
will produce breezy to windy conditions Sunday afternoon and early
evening. Strongest winds are expected along the north coast and
in the vicinity of the east entrance to the strait where gusts of
40-45 mph look likely.

Snow levels will fall sharply late Sunday night...to between 500
and 1000 feet. Strong westerly flow aloft will continue to pile up
the snow in the Cascades with storm totals of 1 to 3 feet
expected by Monday afternoon. The lowlands will see a mix of rain
and snow showers by early Monday morning, but onshore flow will
keep snow levels above sea level most areas. The exception will be
around some heavier showers and/or a convergence zone Sunday
night into early Monday which have a way of pulling the snow level
down lower than the ambient air mass. This could result in a quick
inch or two of accumulation around places like North Bend and will
bear some watching. Precip mostly comes to a short-lived end by
late Monday night and, with any clearing, temperatures will drop
to near or a little below freezing across a good swath of the
lowlands early Tuesday A.M.

.LONG TERM /TUESDAY THROUGH FRIDAY/...Another potent system is
expected to spread rain and mountain snow back across Western
Washington Tuesday night into early Wednesday. It will, at least
temporarily, introduce a somewhat milder air mass with snow levels
climbing back to 3000 to 3500 feet. Ensembles are fairly
confident that this will also be a wetter system. Mountain passes
stand to pick up another substantial helping of snowfall with more
potential travel impacts. Much like Monday and Tuesday, snow
levels are expected to fall sharply again late in the week as a
broad, cold upper trough settles over the Pacific Northwest. 27

&&

.AVIATION...Northwest flow aloft turning westerly into Sunday.
Southwest surface flow across the interior terminals and westerly at
HQM and CLM. Brief wind gusts from 15 to 20 kt cannot be ruled out
through the early overnight before winds and gusts increase Sunday
morning as the pressure gradient tightens with a cold frontal
passage over the region. Wind gusts from 20 to 25 kt likely with a
60% chance for gusts to 30 kt at BFI and BLI after 18Z. Winds
quickly shift to the northwest with a strong onshore push behind a
cold front around 00Z Sunday at PAE with a 35% chance for wind gusts
to 30 kt.

Primarily MVFR CIGs this afternoon with light rain at BLI. Scattered
showers and periods of drizzle and mist possible through tonight
before more widespread rains fill in from south to north in
association with the aforementioned cold front after 15Z Sunday
morning. Mostly MVFR CIGs through the day Sunday, though brief
periods of IFR CIGs and VSBYs cannot be ruled out.

KSEA...MVFR CIGs likely through much of the TAF period with a cold
front moving southward across the region Sunday bringing more
widespread light rain by 16Z. Rain shadowing may delay start time
and intensity of rainfall late morning through the afternoon. VSBY
restrictions possible after rain does begin into the afternoon.
Surface winds from the south-southwest 10 to 15 kt with gusts to 25
kt increasing to 15 to 20 kt with gusts to 30 kt possible after 18Z.

Davis

&&

.MARINE...Onshore flow continues with a cold front poised to sag
southward over the area waters Sunday bringing widespread Small
Craft Advisory Winds with potential Gales through the Strait of Juan
de Fuca late Sunday morning and into Admiralty Inlet by mid
afternoon (around 80% confidence). Gale Watches posted through the
Strait Sunday afternoon in result. Northwest flow increases over the
offshore waters Monday behind this front as a weaker cold front
dives southward further inland. Gale Watches posted for the offshore
waters for Monday (60% chance for gale-force gusts).

Seas generally from 5 to 8 feet over the coastal waters this
afternoon but will increase to 8 to 12 feet late tonight then from
15 to 18 feet by Sunday night. Seas look to gradually lower by
Tuesday, though hovering around 10 feet through the middle of the
week.

Davis

&&

.HYDROLOGY...No river flooding is in the forecast over the next 7
days, but moderate to heavy precipitation will enter the region into
next week. This precipitation may contribute to river rises across
Western Washington with the Skokomish River being the most
sensitive. However, with lower snow levels expected this should help
to abate flood potential.


&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Warning from 4 AM Sunday to 4 PM PST Monday for
     West Slopes North Cascades and Passes-West Slopes North
     Central Cascades and Passes.

     Winter Storm Warning from 10 AM Sunday to 4 PM PST Monday for
     West Slopes South Central Cascades and Passes.

PZ...Small Craft Advisory until 10 PM PST this evening for Central
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 10 PM this evening to 10 PM PST Sunday
     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.

&&

$$


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