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Area forecast discussion
National Weather Service Seattle Washington
302 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...a weather system will move onshore this afternoon
and early evening. Snow has already been falling at the coast and
north interior. Snow at times is expected to develop elsewhere
this afternoon. Advisory amounts for the northwest interior and
near the Cascade foothills look on track. Accumulations elsewhere
should be an inch or less although spotty higher amounts in places
are not out of the question. The central sound area, including
Seattle will be a bit shadowed and snow accumulations are
expected less than an inch. Southerly flow near the surface has
been increasing today. This should help lift snow levels are few
hundred feet tonight and turn snow to rain this evening for most
areas.

A second upper short wave will drop down from the northwest late
tonight with another shot of precipitation. Snow levels should be
high enough, at least initially, for precipitation to be in the
form of rain most areas but there could be problem areas like
Whatcom County near the Canadian border, near the Cascade
foothills, the Hood Canal area, and in a possible Puget Sound
convergence zone over Snohomish County. There is also the chance
rain could change to snow for a good part of The Lowlands for a
few hours Saturday morning as snow levels briefly lower again.
Precipitation will be ending around this time so accumulations
Saturday morning for most areas are not expected at this time.

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...moderate northwest flow aloft will continue tonight
and Saturday. The front over western Washington this afternoon
will move east of the Cascades this evening. An upper trough will
move southeast across the area late tonight and Saturday morning. The
air mass will be moist, mainly below 10,000 ft. At the surface,
moderate southerly flow will continue.

There is a wide range of conditions across western Washington this
afternoon. Where snow or rain is falling, conditions are generally
MVFR to locally IFR due to cloud cover and reduced visibility.
However, the central Puget Sound region is largely in the
precipitation shadow for now, and ceilings at ksea, kbfi, and kpae
were still 6000 ft or higher at 2 PM. Conditions should
deteriorate a bit more through evening. Gradual improvement is
likely Saturday, especially in the afternoon.

Ksea...south wind 8-14 kt rising to 10-16 kt gusting 25 kt during
the next couple hours, veering to southwest late tonight and
probably northwest Saturday afternoon. Conditions should
deteriorate to low-end MVFR by early evening, with around a half
inch of snow possible by 8 PM. There should be gradual improvement
Saturday, with VFR ceilings below 6000 ft likely Saturday
afternoon. Mcdonnal

&&

Marine...the front over western Washington this afternoon will
move east of the Cascades this evening, followed by strong
westerly flow tonight and Saturday. Small craft advisories remain
in effect for all marine zones.

A stronger front will move through the area Saturday night and
Sunday. A gale watch has been issued for the coastal waters and
Strait of Juan de Fuca beginning midnight Saturday night and
continuing into Sunday. Weak high pressure over the area Monday
will be followed by another front on Tuesday. Mcdonnal

&&

Hydrology...river flooding is not expected for the next 7 days.

&&

Sew watches/warnings/advisories...
Washington...Winter Weather Advisory until noon PST Saturday for Cascades of
Pierce and Lewis counties-Cascades of Snohomish and King
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 noon PST Saturday for 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 from 6 am Saturday to 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 until 6 PM 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 midnight PST tonight for Admiralty
Inlet.

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

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