Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 181608

Area Forecast Discussion
National Weather Service Seattle WA
808 AM PST Thu Jan 18 2018

.SYNOPSIS...Moist southerly flow will continue today for
additional showers and a slight chance of thunderstorms. Large
waves generated by a deep low pressure offshore will impact the
coast today. Friday through Saturday will be showery with an upper
trough over the area. Additional fronts will move through the
area Sunday and Tuesday or Tuesday night.


.SHORT TERM...An upper trough will maintain moist unstable flow
over the area the next few days. Weak short waves in the flow
aloft will enhance showers at times. A Puget Sound Convergence
Zone is also possible around Saturday morning.

There is a slight chance of thunderstorms today with cold air
aloft. The thunder threat should end after today with slightly
more stable air developing. Large swell - 25-30 feet - at the
coast will gradually subside tonight and Friday.

Winds will be breezy at times the next few days with a deep
surface low off the British Columbia coast. The mountains will
pick up several inches of snow over the next few days. There might
be advisory amounts at times but it will be hard to pin down
accumulations that precisely with the showery nature of the
precipitation. Schneider

.LONG TERM...Previous discussion...The forecast will remain
unsettled through the middle of next week as a series of fronts
track through the region. Temperatures are trending a few degrees
below normal. The models are trying to build a ridge over the Pac
NW late next week but a warm front over B.C. is clipping us for
some rain. No major changes from the previous forecast. 33


.AVIATION...An upper trough will move ashore over the west coast
of the U.S. through Friday. Strong SW flow aloft today will become
light west flow Friday. The air is moist and unstable with
scattered showers. A few thunderstorms are possible this
afternoon-- although the most unstable air will move into Western
Oregon tonight under the coldest air aloft there.

KSEA...Scattered showers and breezy at times. We will watch the
radar and see if any thunderstorms or squalls develop--but the best
chance of that is out on the coast.


.MARINE...A deep low will gradually fill as it slowly moves to the
north tip of Vancouver Island Friday. Strong southwest flow will
continue through tonight with gales over the coastal waters and
widespread small craft advisory conditions at times over the inland
waters. Weaker troughs will move through the waters Friday night and
Saturday. Fronts will affect the region Sunday, Tuesday and Wed.


.HYDROLOGY...Heavy rain from a frontal system could cause minor
flooding on the Skokomish river in Mason county later Sunday or
Sunday night. Otherwise, river flooding is not expected for the
next 7 days.


WA...Coastal Flood Warning until 10 PM PST this evening for Central
     Coast-North Coast.

PZ...Gale Warning until 10 PM PST this evening 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 Friday for
     Grays Harbor Bar.

     Small Craft Advisory until 4 AM PST Friday for Admiralty Inlet-
     East Entrance U.S. Waters Strait Of Juan De Fuca-Northern
     Inland Waters Including The San Juan Islands-Puget Sound
     and Hood Canal-West Entrance U.S. Waters Strait Of Juan De


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