Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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512
FXUS66 KSEW 240426
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
826 PM PST Fri Feb 23 2018

.SYNOPSIS...Cold and unsettled weather will continue through next
week. A weather system will move through the area later today and
tonight with lowland snow transitioning to rain. Another system
will cross the area Saturday night and Sunday with local lowland
snow possible again. There will be a bit of a break on Monday
before more systems arrive in the middle of the week.

&&

.SHORT TERM...The low level air mass will continue to moderate
tonight as S/SW flow advects warmer air inland. The profiler here
in north Seattle shows a spike in the freezing level up to 500
meters with south flow. The coast has changed over to rain but
still seeing a rain/snow mix in the interior, especially north and
south sound. Seattle is getting shadowed due to westerly flow off
the Olympics. The focus tonight will be on a developing Puget
Sound Convergence Zone that will likely form over Snohomish county
then shift south into King county early Sat morning. Snow levels
are still low enough that areas near the Cascades may see
accumulating snow. Heavy snow is still expected in the Cascades
and passes - Winter Weather Advisories remain in effect. 33

Previous discussion...There will be a bit of a break later
Saturday in between weather systems. Yet another cold upper short
wave will drop down from the northwest Saturday night and Sunday
morning. There is enough uncertainty with the details that another
shot of lowland snow cannot be ruled out but, at least for now,
snow levels are expected to be high enough to preclude any
impactful lowland snow accumulations.

The mountains will also pick up a quite a bit of snow through
Sunday. High end advisory amounts are expected tonight and
Saturday morning. Another round of heavy snow is possible
Saturday night and Sunday. A winter weather advisory is in effect
for tonight and Saturday morning. A winter storm watch is in
effect for Saturday night and Sunday.

It also looks breezy to windy at times the next couple of days.
Winds are expected to remain below advisory levels.

Monday will be a relative lull in the wet weather but cool north
to northwest flow aloft will continue with weak embedded short
waves. Some rain or snow showers cannot be ruled out but
significant lowland accumulations are not expected. Schneider


.LONG TERM...Cool and unsettled weather will continue Tuesday
through Friday. Additional upper troughs will move through the
area but models are not in good agreement with the details. The
general idea is for continued showery weather at times with low
snow levels and below normal high temperatures. Low level onshore
flow will continue but the air will be cold enough for the threat
of lowland snow at times. Schneider

&&

.AVIATION...A cool upper level trough will maintain rain/snow
showers across Western Washington tonight. The air mass is moist
with W/NW flow aloft. MVFR to IFR ceilings are expected through
Saturday morning. Heavier showers from a Puget Sound Convergence
zone is expected over Snohomish/King counties from 12-18z. 33

KSEA...A mix of rain/snow showers tonight with accumulations under
1 inch. Temperatures will remain above freezing. S/SW flow 10-15
kt. MVFR to IFR cigs through Sat morning. 33

&&

.MARINE...Strong westerly flow will develop tonight behind a
front with gales likely through the Strait of Juan de Fuca. Expect
Small Craft Advisory winds elsewhere. A stronger system will
impact the region Saturday night and Sunday with gales possible
again - Gale Watches are in effect. Seas will also build to 14 to
20 feet during this period. Weak high pressure will bring lighter
winds on Monday. Another cold front will arrive on Tuesday. 33

&&

.HYDROLOGY...River flooding is not expected for the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until noon PST Saturday for Cascades of
     Pierce and Lewis Counties-Cascades of Snohomish and King
     Counties-Cascades of Whatcom and Skagit Counties.

     Winter Storm Watch from Saturday evening through Sunday
     afternoon for Cascades of Pierce and Lewis Counties-
     Cascades of Snohomish and King Counties-Cascades of Whatcom
     and Skagit Counties.

     Winter Weather Advisory until 8 PM PST this evening for San Juan
     County-Western Skagit County-Western Whatcom County.

     Winter Weather Advisory until 4 AM PST Saturday for East Puget
     Sound Lowlands.

PZ...Small Craft Advisory for rough bar until 6 AM PST Sunday for
     Grays Harbor Bar.

     Gale Watch from late Saturday night through Sunday morning 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.

     Small Craft Advisory until midnight PST Saturday night 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.

     Gale Watch from late Saturday night through Sunday afternoon for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 7 AM to 6 PM PST Saturday for Central
     U.S. Waters Strait Of Juan De Fuca-East Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Gale Warning until 7 AM PST Saturday for Central U.S. Waters
     Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory until 6 AM PST Saturday for Northern Inland
     Waters Including The San Juan Islands.

     Small Craft Advisory until 7 AM PST Saturday for Admiralty Inlet.

     Small Craft Advisory until 4 AM PST Saturday for Puget Sound and
     Hood Canal.

&&

$$

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