Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 210428
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
928 PM PDT Fri Apr 20 2018

.SYNOPSIS...A cold front will move eastward across the area
overnight with decreasing showers behind the front Saturday. A
dry upper trough will cross the area Sunday. An upper level ridge
will build in Sunday night and remain over Western Washington
through most of next week for an extended dry and warm spell.

&&

.SHORT TERM...A cold front will bring a quick shot of rain to
most of the area later tonight. Rain is already nearing the coast
right now and will move across the metro area between about 1-4
AM.

Onshore flow behind the front will moisten the air mass, but
showers behind the front will mainly be confined to the mountains
Saturday. Moderate onshore flow will produce breezy to locally
windy conditions behind the cold front. A Puget Sound Convergence
Zone will slip southward from Everett to Seattle during Saturday
afternoon and early evening, accompanied by a few showers and a
localized band of stubborn clouds. Temps will be a few degrees
cooler compared to today but still close to normal.

Sunday is looking dry with decreasing clouds. A weak upper trough
will cross the area in the morning with an upper upper ridge
building in from the west later in the day. Highs will once again
be near normal. The upper ridge will move overhead on Monday for
dry and warmer weather. Haner

.LONG TERM...From Previous Discussion: High pressure aloft will
produce mostly sunny and warm weather Tuesday through Thursday.
Highs will warm into the 70s many areas. Thursday will probably be
the warmest day
- possibly near 80 in spots with low level offshore flow. Onshore
flow is expected to develop Friday which should cool highs back
into the 60s. Some showers could also move into the area from the
south. Schneider

&&

.AVIATION...A quick-moving upper trough and surface cold front
will sweet eastward across Western Washington late tonight,
accompanied by a 1-2 hour bout of rain. It will be followed on
Saturday morning by onshore flow, which will bring plenty of cigs
in the 015-030 range in the hours around and after sunrise. Clouds
will scatter and lift in the afternoon, but a Puget Sound
Convergence Zone will from near Everett early in the day and slip
south past Seattle by late afternoon, bringing localized showers
and broken cigs.

KSEA...Cold frontal passage expected around 09z-11z, bringing
lower cigs along with about 2 hours of rain. Could briefly be
heavy enough to reduce vsbys to 5-6SM. Early Sat morning,
expecting cigs in the 020-030 range given onshore flow. Cigs will
lift in the afternoon. Then a PSCZ will slip down from the north,
bringing a few showers in the 22z-02z time frame, a thickening of
clouds, and a northerly wind shift around 00z-01z. Haner

&&

.MARINE...A cold front will sweep eastward across the waters late
tonight, followed on Saturday morning by a few hours of strong
onshore flow and westerly gales in the Central/Eastern Strait.
Seas along the coast will exceed 10 feet from late tonight into
Saturday afternoon.

High pressure will build into the area later Saturday and into
Sunday. A thermal trough will set up along the Oregon coast Monday
and Tuesday, so we will see northerly breezes develop over
Western Washington Monday and Tuesday-- perhaps stronger than the
current forecast and better for afternoon sailing than the current
forecast indicates which only has north winds to 10 knots over
the inland waters for now.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 6 PM PDT Saturday for Admiralty Inlet-
     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-Northern Inland
     Waters Including The San Juan Islands.

     Small Craft Advisory for rough bar from 3 AM to 6 PM PDT
     Saturday for Grays Harbor Bar.

     Gale Warning from 3 AM to noon PDT Saturday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 3 PM PDT Saturday for West Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until noon PDT Saturday for Puget Sound and
     Hood Canal.

&&

$$

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