Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 200410
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
910 PM PDT Sat Aug 19 2017

.SYNOPSIS...Light onshore flow will give some areas of low clouds in
the late night and morning hours through Monday. The areas of night
and morning low clouds and fog should mainly on the coast and near
the water. High pressure will shift over the region Monday and
Tuesday for warmer temperatures. A trough will bring cooler weather
and a chance of showers late Wednesday and Thursday. High pressure
will build over the area again toward the end of the week.

&&

.SHORT TERM...A few areas of low clouds should form along the
coast late tonight and there might be a few patches inland. Light
northwesterly onshore flow will give another nice day on Sunday
with highs into the 70s across much of the interior. Upper ridging
amplifies just offshore Sunday night then progresses eastward across
the region Monday and into Western Montana Tuesday afternoon. This
ridge will give sunny weather except for shallow morning low clouds
and fog--but mainly for the coast and over the waters. Around Puget
Sound and up through the inland waters fog or low clouds should burn
off over land pretty quickly but could linger through mid morning
over the water.

.LONG TERM...Onshore flow later Tuesday will usher in a marine
push Tuesday afternoon and evening that will result in increased
clouds. The push will be followed by a frontal system that will
move across the area Wednesday night and a rather deep upper level
trough Thursday through Thursday night. Long term models appear to
be converging on a solution (between the GFS and ECMWF) where
there will be a threat of showers Wednesday afternoon through
Thursday evening. Thursday high temperatures will likely not reach
the 70 degree mark across most of the area with the clouds, some
showers, and the cooler air mass. Snow levels are expected to fall
to 6000 to 7000 feet in the North Cascades Thursday or Thursday
night, and may impact campers and backpackers at higher
elevations.

As high pressure builds into southeastern British Columbia Friday
through the weekend, offshore flow will give a good warming and
drying trend. Albrecht

&&

.AVIATION...Northwest flow aloft over Western Washington tonight
and Sunday as an upper ridge remains over the offshore waters. At
the surface, onshore flow will continue with high pressure
offshore and lower pressure east of the Cascades.

Just some high clouds over most of the area through Sunday.
Shallow marine layer along the coast with mvfr ceilings
developing for a few hours Sunday morning.

KSEA...Just some high clouds at times through Sunday. North
northeast wind 5 to 10 kt backing to northwest again midday Sunday.
Felton

&&

.MARINE...A typical August pattern will prevail through the
middle of next week. Expect onshore flow of varying strength to
persist due to high pressure offshore and lower pressure east of
the Cascades. A weak system will approach the coastal waters on
Wednesday and move inland Thursday. Small craft advisory west
winds are likely in the central and eastern Strait of Juan de
Fuca in the evening and early morning hours each night. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Sunday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

&&

$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html


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