Small Craft Advisory 7, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
912 PM PST Sat Jan 11 2020

.SYNOPSIS...Gusty winds, rain and heavy mountain snow will
continue tonight with strong onshore flow. Fraser River outflow
winds will develop Sunday and the snow level will fall to sea
level as the cold air pushes south through Sunday evening .Cold,
dry air will be over the area Monday and Tuesday before another
weather system arrives around the middle of the week.

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.SHORT TERM /TONIGHT THROUGH TUESDAY/...Radar this evening shows
rain spreading along the coast as a frontal system approaches the
Pacific Northwest. Rain at times tonight with mountain snow (snow
levels 1500-2000 feet) into early Sunday morning. A Winter Storm
Warning in effect for the mountains through Sunday. Temperatures
tonight will be in the mid to upper 30s.

Sunday will feature strong winds for Whatcom and the San Juan's
as Fraser Outflow develops late Sunday afternoon with BLI- YWL
gradients 21-23 mb. Winds will be rather gusty through Monday as
gradients stay elevated with high pressure positioned over British
Columbia for offshore, easterly flow.

Lowland snow potential Sunday as cold air filters into Western
Washington from north to south during the afternoon and overnight
hours. However, there are a few uncertainties surrounding how
widespread snow will be as well as exact amounts, especially
across portions of the central Puget Sound. Lowland rain Sunday
morning will transition to wet snow initially for Whatcom County
Sunday afternoon as cold air filters into this area. The exact
track of the low pressure system will impact the timing of the
transition of rain to snow for northern areas, with most guidance
highlighting a track along Vancouver Island and into the Northern
Inland waters by Sunday afternoon. Snow levels will lower Sunday
evening into Sunday night as cold air filters elsewhere across
Western Washington and an arctic front slides through. Rain
showers will transition to light snow for most by Sunday evening.
Another uncertain aspect to the forecast is a possible Puget
Sound Convergence Zone - which some hi-res guidance does have
developing. Guidance has started to 'converge' on the
King/Snohomish solution for the location of the possible PSCV.
With that said, if Fraser Outflow becomes the dominant mean for
convergence (rather than strong onshore push), it is possible the
PSCV is more progressive and develops farther south (near or
south of Seattle) with drier air over Western Washington. Still,
opting to go with King/Snohomish PSCV given the HREF short-range
forecasts, and will need to be monitored. Winter Storm Watch in
effect for much of the Puget Sound area with a trace-2" for most
(up to 4" in PSCV), and 2-6" for Whatcom/Foothills. Elevated
snowfall amounts will also be possible for the Strait of Juan de
Fuca in Clallam County depending on the timing of the Fraser
Outflow prior to drier air expected on Monday.

Precipitation (light snow) is expected to linger into Monday
morning for portions of the southern tier (south of Olympia) with
an additional trace-0.5" possible. Otherwise Monday will feature
colder temperatures across the area with highs in the 20s and 30s.
Fraser outflow winds through Monday for Whatcom/San Juan's with
gusts up to 60 MPH possible.

Tuesday is expected to be dry for Western Washington with offshore
winds. The primary impact will be cold temperatures Tuesday with
highs sub-freezing for most. JD/33

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...Western WA will continue to
see cold weather through next week. Lows will be in the teens to 20s
with highs only around 30 degrees. Our next system will clip the
region Wednesday and Thursday for another chance at lowlands snow
(across all of western WA). This may bring more widespread
snowfall amounts to the region - a more classic overrunning
pattern. The flow remains offshore through the end of the week as
snow levels remain low. Temperatures do moderate a bit as Fraser
outflow winds ease and temps by Friday may reach the low 40s.
However, as mentioned, we may still see a rain/snow mix in the
lowlands with low snow levels. The air mass will continue to
moderate on Saturday for mainly rain in the lowlands. 33

&&

.AVIATION...Northwesterly flow aloft will transition more westerly
on Sunday as a weather system slides through. The air mass is
moist and stable. Unsettled weather through Sunday as widspread
rain moves into the area. MVFR through tonight with IFR for some,
especially early Sunday morning with the front. Southerly winds
sustained 10-15 knots through Sunday with gusts up to 25 knots.

KSEA...MVFR through most of tonight. IFR possible early Sunday
morning. MVFR through Sunday. South winds 10-15 knots with gusts
20-25 knots. JD

&&

.MARINE...Several shortwave troughs will swing down into western
Washington from just offshore the BC Coast overnight tonight and
thru the day on Sunday. A sfc reflection will accompany these
waves, especially the one set to drop down through the day on
Sunday. A glance further north and northeast of the water reveals
a very strong sfc high pressure system residing across BC and
Alberta. This high will slide south through the day Sunday and
overnight Sunday into Monday, some of which will bleed down the
Fraser River Valley. This setup will have important implications
to the marine forecast.

Sfc low just offshore BC is expected to yield a southerly component
to the wind overnight tonight into Sunday. Given strong high
pressure in the vicinity across Canada, gradients will be strong.
Winds will at least reach small craft advisory criteria. Have opted
to keep gale warning for the coast, tho do think there will be a
period of time overnight winds will ease before ramping back up
quickly to gales Sunday morning. By the afternoon, Fraser outflow
should reach the N Inland Waters, marking the arrival of the cold
Canadian air. Gale warnings will remain in place all the way into
Monday. Think these winds could also reach gale force across the E S
trait and Admiralty Inlet, so have a warning going into Monday as
well. Winds should relax some by Monday tho will still likely need
to introduce more SCA headlines. Will leave that for future updates,
with the emphasis now being on the near-term. Snow is likely across
the northern waters on Sunday, and with the wind, will likely reduce
visibility at times.

In addition to winds, Small Craft for rough bar conditions at
Grays Harbor has been extended into Monday. Altho swells are
relaxing this afternoon and are not expected to build as high as
they were Friday night/Sat, they will still remain above 10ft.
Will also need to closely monitor Toke Point area for minor
coastal flooding early Sunday.

Active marine weather is likely to continue for much of the week.

JD/Kovacik

&&

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

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Watch from Sunday afternoon through late Sunday
     night for Admiralty Inlet Area-Bellevue and Vicinity-
     Bremerton and Vicinity-East Puget Sound Lowlands-Eastern
     Strait of Juan de Fuca-Everett and Vicinity-Hood Canal Area-
     Seattle and Vicinity-Tacoma Area-Western Strait of Juan De
     Fuca.

     Winter Storm Warning until 4 PM PST Sunday for Cascades of
     Pierce and Lewis Counties-Cascades of Snohomish and King
     Counties-Cascades of Whatcom and Skagit Counties.

     High Wind Warning from noon Sunday to 7 AM PST Monday for San
     Juan County-Western Whatcom County.

     Winter Storm Watch from Sunday afternoon through Sunday evening
     for San Juan County-Western Skagit County-Western Whatcom
     County.

     Wind Advisory from noon Sunday to 7 AM PST Monday for Western
     Skagit County.

PZ...Small Craft Advisory until 10 AM PST Monday for Grays Harbor Bar-
     Puget Sound and Hood Canal.

     Gale Warning until 10 PM PST Sunday 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.

     Gale Warning until 10 AM PST Monday for East Entrance U.S.
     Waters Strait Of Juan De Fuca-Northern Inland Waters
     Including The San Juan Islands.

     Small Craft Advisory until 10 AM PST Monday for West Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Gale Warning until 8 PM PST this evening for West Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 10 AM PST Monday for Central U.S.
     Waters Strait Of Juan De Fuca.

     Gale Warning until 10 PM PST this evening for Central U.S.
     Waters Strait Of Juan De Fuca.

     Gale Warning until 10 AM PST Monday for Admiralty Inlet.

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