Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 181056

Area Forecast Discussion
National Weather Service Seattle WA
256 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
Washington coast today. Friday through Saturday will be showery
with an upper trough over the area. Additional fronts will move
through the area Sunday and around Tuesday night.


.SHORT TERM...Coastal Flood update...Strong southwest winds
offshore have generated a large and energetic swell of 30-35 ft
at 18 or 19 seconds that are moving onto the coastline. The swell
will continue through this evening before slowly diminishing.
Waves will run up on beaches far beyond where they normally do
producing significant beach erosion. The breaking waves will
result in a piling up of water along the coastline. Low
atmospheric pressure and southwest winds are contributing to tides
that are running 1.5 feet above predicted values. The combination
of all of these effects will result in saltwater flooding in low-
lying coastal communities such as Ocean Shores, Westport, and

A strong Pacific system sent a cold front inland overnight for
gusty winds, heavy showers and thunderstorms. The threat for
additional showers and thunderstorms will continue today as the
southerly 150kt jet shifts east of the crest. The surface low,
around 965 mb off Haida Gwaii, will gradually stall then
fill/weaken through Friday. By Friday night, the low is around 995
mb as it passes inland through the Queen Charlotte Sound.

Friday will be cool and unstable with a deep trough over the
West. The cooler air mass will knock snow levels down to around
2,000 ft in the mountains. We may see a brief break on Saturday
with weak upper level ridging. Sunday is looking more active as a
wetter frontal system moves inland. It`ll be windy along the
coast and north interior with heavy snow possible in the
mountains. 33

.LONG TERM...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...Strong southwest flow aloft will continue through
tonight around a strong and expansive low that is sitting about
200 nm west of the northern tip of Vancouver Island. The air mass
moving around this low is moist and unstable. Showers can be
expected across the area through tonight. There will be a threat
of thunderstorms this morning in the interior and through this
evening along the coast. Ceilings and visibilities will be
variable with VFR to MVFR conditions between showers, and
conditions dropping to lower end MVFR to IFR in heavier showers.

KSEA...Expect showers with gusty south to southwest winds through
tonight. South winds generally 12-15 knots with gusts 22-25
knots. Ceilings 050 will drop to 2500 ft at times in heavier
showers. Visibilities P6SM falling to 3-5SM in heavier showers.


.MARINE...A deep low centered near 51N 134W 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 over the inland waters. Conditions will slowly improve
late Thursday night and Friday.

Weaker troughs will move through the waters Friday night and
Saturday. A series of rather strong fronts will move across the
waters Sunday through the middle of next week. Albrecht


.HYDROLOGY...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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