Small Craft Advisory 314, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
430 AM PST Fri Dec 29 2017

.SYNOPSIS...Active weather will continue through this evening with
lowland rain, breezy to windy conditions for the central Washington
coast and much of the interior as well as a wintry precipitation mix
for the Cascades and passes. A few rivers could also reach minor
flood levels tonight into Saturday morning. Lingering showers should
end on Saturday as higher pressure builds over the region with dry
weather expected to persist into the start of the new year.

&&

.SHORT TERM...Radar and satellite imagery showing rain over roughly
the south two thirds of the forecast area this morning, with a few
isolated showers along the Canadian border to the north.
Temperatures in much of Western Whatcom County continue to linger
just below freezing, especially away from the water. The freezing
rain advisory remains in effect there until 7 AM.

Precipitation will increase as a warm front continues to work into
Western Washington this morning and continue this afternoon and
evening as the associated cold front moves onshore. For the
Cascades, the ongoing cool easterly flow through the passes and
fluctuating snow levels is expected to keep a mix of snow, freezing
rain and even a little sleet in Snoqualmie and Steven passes,
resulting in messy weather there with hazardous driving conditions.
Over the north, lower snow levels will result in heavier snow
accumulations over the Whatcom and Skagit County Cascades. A winter
storm warning is in effect through 10 PM this evening for the King
County Cascades northward. Higher snow levels over the south will
help limit the impact of snowfall over the Pierce and Lewis County
Cascades to the highest ridges and Mount Rainier with rain falling
over most other locations.

Models continue to show a strengthening surface low moving onshore
late this afternoon, bringing the surface low across the Olympic
Peninsula and into the north interior during the evening. This
pattern will result in advisory level southerlies to the south of
low along the central coast during the afternoon followed by the
interior from Admiralty Inlet southward this evening. In addition to
the southerlies, as the low shifts inland expect a burst of
westerlies that will affect the eastern Strait, Admiralty Inlet and
western Skagit County later this evening. A wind advisory has been
issued to reflect the winder conditions. Winds will ease from west
to east late tonight.

The upper trough trailing the surface fronts will move onshore
overnight into Saturday with showers tapering off during the day.
Upper level ridging will build offshore setting the stage for dry
weather into early next week.

.LONG TERM FROM THE PREV DISCUSSION...The upper level ridge will
shift onshore Monday with high pressure will gradually weaken
Tuesday through Thursday. This will allow a few weak systems to
brush the area area resulting in what looks to be a few periods of
light precipitation.

&&

.AVIATION...An upper level trof offshore will continue moving east
today. The frontal system associated with the trof will move across
the area this evening. The flow aloft will be strong westerly. Low
level offshore flow will become strong onshore in the wake of the
front. Meanwhile, expect widespread MVFR CIGs/VSBYs and areas of IFR
CIGs today. The mtns will be obscd.

Meanwhile, cold northerly winds across the Fraser River Valley were
keeping temps near freezing. This has resulted in areas of -FZRA
over parts of the lower elevations of western Whatcom County.
Northerly winds will persist throughout the day today and will
actually strengthen. Therefore, expect -FZRA to continue over this
area. Ice accumulations are anticipated to be less than a quarter of
an inch. This will impact KBLI. Winds are forecast to switch out of
the southeast early this evening, and this will cause temperatures
to jump into the 40s and end any FZRA threat.

KSEA...Anticipate LIFR CIGs to lift into the IFR category range (500-
1000 ft) by early this afternoon. CIGs are expected to be in the 1-
3K ft range this afternoon through late this evening, possible
lifting into VFR category tonight. Visibilities will generally be in
the 3-5SM range during the day today, improving to P6SM late this
evening. Expect strong southerly winds to develop with the passage
of the cold or occluded front late this evening. Winds will diminish
Saturday morning.

&&

.MARINE...
A 1009 mb low off the Oregon coast will strengthen to near 1000 mb
as it approaches Cape Flattery late this afternoon. The low will
weaken to 1005 mb as it moves across the interior waters this
evening. The frontal system extending from the low will move across
the coastal waters later today, and then the interior waters this
evening. Strong onshore flow behind the cold front will weaken on
Saturday.

The track and strength of today's surface low was still uncertain.
If it tracks farther north or across mainland British Columbia,
winds could reach gale force over a larger area, especially if the
low ends of being stronger than forecast. At this time, going with
gale force winds across much of the coastal waters, Strait of Juan
de Fuca, and Puget Sound/Hood Canal. There were some indications
that westerly winds could briefly reach storm force over parts of
the Strait of Juan de Fuca, hence the Storm Watch.

&&

.HYDROLOGY...
There will be heavy rain at times in the mountains tonight and
Friday. The area of heaviest rain will drift south tonight, then
move back north Friday. The snow level will be around 5000 feet
south and 3000 feet north on Friday. Then a cold front will move
through the region Friday night, lowering the snow level below
2000 feet and ending any heavy rain.

A few rivers could have minor flooding from this event. The most
likely flooding will be on flood prone rivers in the southern half
of the CWA, such as the Skokomish River in Mason County, the
Snoqualmie River near Carnation and the White River at R Street
bridge in Auburn, both in King County, and the Newaukum River in
Lewis County. A flood watch is in effect for the southern two-thirds
of Western Washington. It highlights the possibility of minor
flooding on a few rivers. Burke

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch from this afternoon through Saturday afternoon for
     Admiralty Inlet Area-Bellevue and Vicinity-Cascades of
     Pierce and Lewis Counties-Cascades of Snohomish and King
     Counties-Central Coast-East Puget Sound Lowlands-Eastern
     Strait of Juan de Fuca-Everett and Vicinity-Hood Canal Area-
     Lower Chehalis Valley Area-North Coast-Olympics-Seattle and
     Vicinity-Southwest Interior-Tacoma Area-Western Strait of
     Juan De Fuca.

     Wind Advisory from 6 PM this evening to 4 AM PST Saturday for
     Admiralty Inlet Area-Bremerton and Vicinity-East Puget
     Sound Lowlands-Eastern Strait of Juan de Fuca-Hood Canal
     Area-Lower Chehalis Valley Area-Seattle and Vicinity-
     Southwest Interior-Tacoma Area-Western Skagit County.

     Winter Storm Warning until 10 PM PST this evening for Cascades
     of Snohomish and King Counties-Cascades of Whatcom and
     Skagit Counties.

     Winter Weather Advisory until 7 AM PST this morning for Western
     Whatcom County.

     Wind Advisory from noon today to 10 PM PST this evening for
     Central Coast.

PZ...Small Craft Advisory for rough bar from 3 PM this afternoon to 6
     AM PST Saturday for Grays Harbor Bar.

     Gale Warning from noon today to 10 PM PST this evening for
     Coastal Waters From Point Grenville To Cape Shoalwater 10
     To 60 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater Out 10 Nm.

     Gale Watch this evening for Coastal Waters From James Island To
     Point Grenville 10 To 60 Nm-Coastal Waters From James
     Island To Point Grenville Out 10 Nm.

     Small Craft Advisory until 6 PM PST this evening for Central
     U.S. Waters Strait Of Juan De Fuca-Coastal Waters From
     James Island To Point Grenville 10 To 60 Nm-Coastal Waters
     From James Island To Point Grenville Out 10 Nm-West
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 6 AM PST Saturday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From Cape Flattery To James Island Out 10 Nm.

     Gale Watch from this evening through late tonight for East
     Entrance U.S. Waters Strait Of Juan De Fuca-Puget Sound and
     Hood Canal-West Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 10 AM this morning to 4 AM PST
     Saturday for Northern Inland Waters Including The San Juan
     Islands.

     Storm Watch from this evening through late tonight for Central
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 4 PM this afternoon to 6 AM PST
     Saturday for Admiralty Inlet.

&&

www.weather.gov/seattle