Gale Warning 10, NWS Seattle, WA

Area Forecast Discussion National Weather Service Seattle WA 220 PM
PST Mon Feb 6 2023

.SYNOPSIS...A vigorous frontal system will bring lowland rain,
mountain snow, and windy conditions to Western Washington tonight
through Tuesday. Showers linger Wednesday as a trough moves through
the region. High pressure will provide drier conditions much of
Thursday before a weak front arrives on Friday. Unsettled conditions
will then persist into the weekend.

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.SHORT TERM /TONIGHT THROUGH THURSDAY/...Scattered showers
continue across the area this afternoon as a warm front approaches
the offshore waters. Stratiform rain will increase later tonight
into early Tuesday as the warm front lifts northward across the
area. Winds will also increase tonight...with the strongest winds
expected across the North Interior with gusts in the 40 mph range
expected. Snow levels will initially make a jump with the arrival of
the warm front early Tuesday, but will tumble behind a trailing cold
front as it pushes through Puget Sound around midday Tuesday.
Modest instability will follow the front for a slight chance of
thunderstorms coastal areas.

Strong post-frontal onshore flow should get a convergence zone going
late Tuesday afternoon through Tuesday night before it eventually
dissipates in the Cascades Wednesday morning as onshore gradients
gradually relax. Winter storm criteria snowfall looks likely for the
North Cascades with 1 to 2 feet expected in the Mount Baker area.
Further south, amounts look a little lighter, but the post- frontal
environment will be favorable for 8-12 inches at Snoqualmie Pass by
early Wednesday and 14-18 inches at Stevens. There is one caveat to
be aware of though. If the convergence sets up for an extended
period over the passes Tuesday night, these totals could easily be
adjusted upward.

Weak ridging aloft will build into the area Wednesday afternoon into
early Thursday for a drying trend across the area. Thursday looks
dry for most of Western Washington with the exception of the Olympic
Peninsula where some light precip could arrive by evening ahead of a
weak front. Temperatures through the short term forecast period will
be a couple degrees either side of seasonal averages for early
February.

.LONG TERM /FRIDAY THROUGH MONDAY/...Models remain fairly
consistent with the arrival of another frontal system on Friday.
However, deterministic solutions as well as a number of ensembles
show the front rapidly splitting upon arrival. Upper ridging
attempts to establish itself just offshore over the weekend, but
Western Washington remains on the northern periphery of the ridge
with at least chance PoPs as weak systems brush the area. More
uncertainty begins to emerge in the forecast early next week with a
considerable spread in the 500mb cluster plots. This isn't terribly
surprising with a cut-off upper low over the Desert Southwest
greatly affecting what may...or may not...happen upstream over the
Pacific Northwest. 27

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.AVIATION...An upper ridge over the area will shift inland
tonight with an upper trough moving to the coast on Tuesday. The
flow aloft will be westerly. A cold front will move through the area
later tonight and Tuesday morning. Onshore flow will develop behind
the front later Tuesday. A Puget Sound Convergence Zone is expected
to form Tuesday afternoon and linger into Tuesday night.

The air mass will be moist and stable. It will become unstable
behind the front on Tuesday, especially near the coast. Low clouds
will be fairly widespread tonight and Tuesday morning with some
drying late in the day Tuesday.

KSEA...Low clouds tonight and Tuesday. Low clouds will probably
scatter late Tuesday afternoon. Gusty south winds. 16

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.MARINE...A cold front will move through the area tonight and
Tuesday morning with small craft advisory strength southerly winds
most waters. Gale force southerly winds are likely for the northern
interior waters tonight. The Coastal Waters could also see some
marginal gale force winds tonight.

A period of onshore flow will follow the cold front on Tuesday,
easing on Wednesday. Gales force west winds are likely for the
Strait Tuesday night. There might some gusts to gale force over the
Coastal Waters as well on Tuesday. A second, weakening frontal
system will move through the area Thursday and Friday.

Combined seas over the Coastal Waters will build to 12 to 16 feet
tonight and remain in that general range through Wednesday before
briefly subsiding below 10 feet Wednesday night and Thursday.
Combined seas will build again to 12 to 16 feet Friday. 16

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.HYDROLOGY...A flood watch remains in effect for Mason County from
Tuesday morning through Wednesday as heavy rain centered over the
region may lead to flooding on the Skokomish River. The river is
currently forecast to rise above flood stage toward midday
Tuesday...and briefly reach moderate flood stage by Tuesday evening.
Elsewhere, river flooding is not expected through the week ahead.

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.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch from Tuesday morning through Wednesday morning for
    Hood Canal Area-Lower Chehalis Valley Area-Olympics.

     Winter Storm Warning from 4 AM Tuesday to 10 AM PST Wednesday
   for West Slopes North Cascades and Passes.

     Winter Weather Advisory from 4 AM Tuesday to 10 AM PST
Wednesday      for West Slopes North Central Cascades and Passes-
West Slopes South Central Cascades and Passes.

PZ...Small Craft Advisory until 3 PM PST Tuesday for Grays Harbor
Bar.

     Small Craft Advisory until 4 AM PST Wednesday 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-Puget Sound and Hood Canal-West
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning from noon Tuesday to 4 AM PST Wednesday for Central
     U.S. Waters Strait Of Juan De Fuca.

     Gale Warning until 4 AM PST Tuesday for Admiralty Inlet-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Watch from Tuesday afternoon through late Tuesday night for
     East Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning until 8 AM PST Tuesday for Northern Inland Waters
     Including The San Juan Islands.

     Gale Watch from Tuesday afternoon through Tuesday evening for
     Admiralty Inlet.

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