Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 230957
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
257 AM PDT Thu Mar 23 2017

.SYNOPSIS...Rain will reach the coast this afternoon and 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...Today will be mostly dry in between weather systems
with weak high pressure aloft. The exception will be the coast
where a frontal system will bring rain in the afternoon. The
front will move onshore this evening for rain all areas, with
decreasing showers behind the front later tonight. The mountains
will pick up some snow but amounts look sub-advisory. There will
also be some breezy to windy conditions coast and north interior.

An upper trough will move over the area on Friday for showers. A
short wave in the flow aloft should enhance showers in the
afternoon. There might even be an afternoon thunderstorm or two
but the chances look marginal enough that thunderstorms were not
introduced into the forecast just yet. 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 for drying. Schneider

.LONG TERM...The pattern will be progressive the first half of
next week with a series of weather systems bringing rainy periods
interspersed with brief periods of relative dry weather in
between. The first frontal system will reach the area Sunday.
Models are in good agreement with this. Beyond, Sunday,
confidence in the details decreases as models differences
increase. There may or may not be another period of more organized
rain Monday night/early Tuesday. There is higher confidence that
a frontal system will bring another batch of rain Wednesday.
Schneider

&&

.AVIATION...Westerly flow aloft over Western Washington early this
morning will back to southwest today as the next frontal system
approaches the region from the west. Strong southwest flow aloft
will accompany the frontal system as it moves through the forecast
area late today and tonight. Except for briefing drying midday
today, the air mass will be moist and slightly unstable.

VFR conditions prevail across the forecast area at this time with
sky cover SCT035 OVC070-090, except isolated showers continue with
local BKN-OVC035. VFR conditions should continue today; ceilings
will probably be above 060 most of the time, except for areas of
SCT-BKN035 this morning. As rain associated with the frontal
system develops tonight, conditions should deteriorate to MVFR on
the coast but generally remain VFR inland with ceilings 035-060.

KSEA...South wind 6-12 kt, increasing to 8-16 kt this evening.
by midnight. KSEA will likely have VFR conditions today with
ceilings mainly above 060, then ceilings 035-060 with rain at
times beginning this evening. McDonnal

&&

.MARINE...A vigorous frontal system about 350 NM west of the
Pacific Northwest coast early this morning will move into the
coastal waters today and inland across Western Washington tonight.
This system should produce fairly solid gales of 30 to 40 kt over
the coastal waters late today through tonight, with fairly brief
gales over the eastern Strait of Juan de Fuca and northern inland
waters this evening into early Friday morning.

A trough will follow the front on Friday, with fairly widespread
small craft advisory winds likely. Weak high pres will build over
the region Saturday for a period of lighter winds. A relatively
weak Pacific frontal system will move through the region Sunday
night. McDonnal

&&

.HYDROLOGY...The White River at R Street near Auburn is forecast to
remain near flood stage through at least Friday, primarily due to
releases from Mud Mountain Dam. Elsewhere, river flooding is not
expected for the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until noon PDT today 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.

     Gale Warning from noon today to midnight PDT tonight 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 until 6 PM PDT this evening for East
     Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
     Waters Including The San Juan Islands.

     Gale Warning from 6 PM this evening to 3 AM PDT Friday for East
     Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
     Waters Including The San Juan Islands.

     Small Craft Advisory from 3 PM this afternoon to 6 AM PDT Friday
     for Central U.S. Waters Strait Of Juan De Fuca-West
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 3 PM this afternoon to noon PDT Friday
     for Admiralty Inlet.

&&

$$

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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