Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 232231
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
330 PM PDT Thu Mar 23 2017

.SYNOPSIS...Rain will spread into the interior this evening as a
front moves onshore. An upper trough will bring showers Friday.
Showers will decrease Saturday as the trough shifts inland.
Additional fronts will reach the area Sunday and around Wednesday.

&&

.SHORT TERM...Rain on the coast is quite apparent in radar, and has
been showing up in surface obs as well. Visible satellite imagery
still shows some clear bits over inland areas, but clouds will be
increasing presently. The front will move onshore this evening
bringing rain to all areas, with decreasing showers behind the front
later tonight. The mountains will get snow--southerly flow aloft
favors the volcanoes but not the passes, so have issued a winter
weather advisory mainly for the volcanoes above about 4000 feet late
tonight through Friday morning. There will also be some breezy to
windy conditions coast and north interior.

An upper trough will move over the area on Friday giving showers.
A shortwave in the flow will enhance showers in the afternoon.
Models have continued to show negative lifted indices spreading from
offshore Friday morning to inland areas Friday afternoon and
evening. Have introduced a slight chance of thunderstorms into the
forecast for Friday afternoon and evening.

The upper trough will slowly shift inland Friday night and Saturday.
There will be enough lingering instability for a continued chance of
showers but the trend should be toward drying on Saturday and
especially Saturday night. Sunday will begin dry but another system
will reach the coast in the afternoon and probably spread rain over
the whole area Sunday evening. High temperatures Friday through
Sunday will be a few degrees below normal. Burke

.LONG TERM...Monday will be showery as an upper trough passes.
Tuesday now looks wetter in the models and have boosted pops,
especially on the coast and in the mountains. Wednesday still
appears to be a day when a front brings rain. Thursday will be
showery at first but could see significant drying later in the day.
Temperatures will be close to normal through the period. Burke

&&

.AVIATION...strong southwest flow aloft through Friday morning as a
trough moves into the Pacific Northwest. Moderate west-southwest
flow aloft by Friday afternoon. Air mass generally moist and stable.
A surface front will reach the coast by around midnight and
dissipate as it slowly moves through Puget Sound Friday morning.
Rain developing over most of Wrn Wa by early this evening, becoming
showers behind a front Friday. Mainly VFR cigs, however brief
periods of MVFR cigs/vis possible with steady rain ahead of the
front later tonight.

KSEA...Southeast wind 8-13 kt, becoming South-Southwest 10-16 kt
gusts to 28 kt Friday. VFR cigs around 7-8k ft lowering rapidly to
around 4k ft as steady rain develops around 02z.

&&

.MARINE...Southeast gales up to 40 kt over the coastal waters this
evening, switching to south or southwesterly late tonight and
gradually easing behind a front. Gale force winds over the east
entrance to the Strait and north inland waters will be more brief
tonight. Small craft winds developing this evening all other waters
including Puget Sound. As gales ease late tonight, small craft
strength winds will linger in most waters Friday in post frontal
onshore flow.

Higher pressure builds over the waters Friday night through
Saturday. Another low will affect the waters late Sunday into
Monday.

&&

.HYDROLOGY...River flooding is unlikely over the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory from 11 PM this evening to 11 AM PDT
     Friday for Cascades of Pierce and Lewis Counties-Cascades
     of Whatcom and Skagit Counties.

PZ...Small Craft Advisory from 3 AM to 5 PM PDT Friday 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.

     Gale Warning until 3 AM PDT Friday 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 for rough bar until 11 PM PDT Friday for
     Grays Harbor Bar.

     Small Craft Advisory until 5 PM PDT Friday for Admiralty Inlet-
     Puget Sound and Hood Canal-West Entrance U.S. Waters Strait
     Of Juan De Fuca.

     Small Craft Advisory until 6 AM PDT Friday for Central U.S.
     Waters Strait Of Juan De Fuca.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html


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