Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 161105
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
305 AM PST Tue Jan 16 2018

.SYNOPSIS...Showers will continue across Western Washington today
with moist southwest flow over the region. A strong system will
head toward southern British Columbia on Wednesday then stall
offshore and gradually weaken through Friday night. This system
will generate large waves which may impact the coast. Unsettled
weather will continue into this weekend with a trough over the
region.

&&

.SHORT TERM...The strong upper level ridge that brought sunny and
warm weather to the region yesterday has now shifted east toward
the Rockies. This opens the door for moist S/SW flow over Western
Washington, steered by a stacked system rotating over the Gulf of
Alaska. Expect more showers today under these conditions with a
slight chance of thunderstorms over the Coastal Waters. There have
been a few lightning strikes off the Oregon coast this morning.
Temperatures are starting mild, near 50, and we should see
temperatures staying in the low to mid 50s this afternoon. Showers
will taper off tonight as this system exits.

A strong Pacific system, around 960 mb, will spin over the
Offshore Waters on Wednesday then stall off Haida Gwaii through
Thursday. This system will gradually fill/weaken to around 1000
mb as it spins off Vancouver Island Friday night. Throughout this
period, expect more rain as moist SW flow continues over Western
WA along with breezy to windy conditions. This system will
generate a large swell train that will reach the coast on Thursday
with seas building to 25 to 30 feet. This would lead to a High
Surf Warning along the coast. 33

.LONG TERM...The forecast remains unsettled through the weekend
with upper level troughing over the West. Showers are likely
through the period. Temperatures are trending close to normal.
We may see a break in the action early next week with weak upper
level ridging. No major changes from the previous forecast. 33

&&

.AVIATION...Moderate southerly flow aloft this morning will turn
westerly this afternoon and tonight. At the surface, moderate
southeasterly winds will continue today and ease tonight. The air
mass is moist and slightly unstable. Rain will become more showery
today.

MVFR ceilings around the west side of Puget Sound will spread to the
east side this morning. There will be improvement to VFR by late in
the morning, though MVFR ceilings in showers will still be possible.

KSEA...Discussion above applies. Southerly wind 10-15 kt today.
CHB

&&

.MARINE...A front over the area will give a few more hours of gale
force winds at the east entrance, then most areas will have small
craft advisory strength winds today.

A deep low will move northeast well off the coast Wednesday and
Thursday. The resulting gradient will bring gales to most waters,
and a gale watch is in effect. More fronts later in the week will
keep the weather vigorous.

Strong southwest winds well off the coast will generate large swells
that will reach the Washington coast Thursday. Models have been
consistent in bringing westerly swells of 25 ft or more to the
coast, with even larger swells offshore. These have the potential to
be the highest seas in at least several years. CHB

&&

.HYDROLOGY...A brief period of heavy rain is possible in the
Skokomish Basin on Wednesday evening. This will cause the river to
rise on Wednesday night and Thursday morning. Current rainfall
forecasts support bringing the Skokomish to within a foot of flood
stage. This will bear watching, as forecast rainfall amounts are
prone to change.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Gale Watch from late tonight through late Wednesday 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-East Entrance U.S.
     Waters Strait Of Juan De Fuca-Northern Inland Waters
     Including The San Juan Islands.

     Small Craft Advisory until 3 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.

     Small Craft Advisory for rough bar until 4 AM PST Wednesday for
     Grays Harbor Bar.

     Gale Warning until 10 AM PST this morning for East Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 4 PM PST this afternoon for Admiralty
     Inlet-Northern Inland Waters Including The San Juan Islands-
     Puget Sound and Hood Canal.

&&

$$

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