Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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277
FXUS66 KSEW 240953
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
253 AM PDT Fri Mar 24 2017

.SYNOPSIS...An upper trough will bring showers today. Showers
will decrease Saturday as the trough shifts inland. The pattern
will remain fairly wet into the middle of next week as a series of
weather systems move through.

&&

.SHORT TERM...A front is currently pushing through the area with
rain changing to showers. The air mass will be unstable enough
for a slight chance of thunderstorms this afternoon and early
evening. The volcanoes will continue to pick up some snow. A
winter weather advisory is in effect through this morning.

Showers will taper tonight and become somewhat confined to the
mountains and coast with the loss of daytime heating. The upper
trough over the area will maintain a chance of showers into
Saturday but the coverage should be less than today. Showers
should come to an end Saturday night as high pressure aloft
briefly moves over the area.

Another frontal system will bring an increasing chance of rain
Sunday. This system is somewhat split and not too impressive but
all areas should see some rain. Rain will move onto the coast in
the morning. The interior will likely be dry until afternoon when
rain will arrive. Schneider

.LONG TERM...An upper trough will shift east of the area Monday
for decreasing showers but there won`t really be any break in the
wet weather as warm front rain from the next frontal system will
already be moving into the area in the afternoon. The warm front
should result in a drippy Monday night. A trailing cold front will
keep rain chances high on Tuesday and Wednesday. Drier weather is
expected on Thursday as an upper ridge builds over the Northeast
Pacific. Schneider

&&

.AVIATION...Strong southwest flow aloft over Western Washington
early this morning will gradually ease through tonight. The front
over the Western Washington interior will move east of the
Cascades this morning, and an upper trough will move west across
the forecast area today and tonight. The air mass will be moist
and weakly unstable.

The widespread rain has become showery during the past hour or
so, and ceilings remain mostly OVC035-050. Conditions are locally
lower, mainly along the coast, with 3-5SM -SHRA BR BKN-OVC011
OVC030. Conditions will improve only marginally today and tonight
with BKN-OVC ceilings mainly 035-060, as an upper trough brings
scattered showers and a slight chance of thunderstorms during the
afternoon and evening.

KSEA...Wind should become south to southwest 6-12 kt during the
next few hours and continue through tonight, with gusts to 22 kt
mainly this afternoon and evening. VFR cigs generally 035-060
through tonight. There is a 20 percent chance of a thunderstorm
in the vicinity of KSEA this afternoon or evening. McDonnal

&&

.MARINE...The front is over the Western Washington interior early
this morning and it should move east of the Cascades this morning.
Gales have ended during the last hour or so, and the gale warnings
will be allowed to expire at 3 am.

A trough will follow the front, moving into the coastal waters
today and inland tonight. It will produce small craft advisory
winds over the coastal waters into tonight, with a small craft
advisory for hazardous seas following that through Saturday. For
the inland waters, the trough will produce marginal small craft
advisory winds through this evening.

Weak high pressure will move across the region Saturday for
lighter winds. The next frontal system will move through the area
Sunday night, with another front approaching on Tuesday. Both of
these systems look relatively weak, and gales appear unlikely.
McDonnal

&&

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

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 11 AM PDT this morning for
     Cascades of Pierce and Lewis Counties-Cascades of Whatcom
     and Skagit Counties.

PZ...Small Craft Advisory until 5 AM PDT Saturday 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 early this morning 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 this evening
     for Grays Harbor Bar.

     Small Craft Advisory until 5 AM PDT Saturday for West Entrance
     U.S. Waters Strait Of Juan De Fuca.

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

     Small Craft Advisory until 5 PM PDT this afternoon for Admiralty
     Inlet-Puget Sound and Hood Canal.

&&

$$

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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