Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 222154
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
254 PM PDT THU SEP 22 2016

.SYNOPSIS...An upper trough will gradually shift south of the
region tonight for dry weather across all of Western Washington
except a chance of showers in the mountains. A weak front will
move inland on Friday for some rain. A strong ridge will bring dry
and warmer weather Saturday through Monday with the warmest
weather in September possible on Monday. A marine push will cool
things down on Tuesday.

&&

.SHORT TERM...Isolated showers may pop up in the Olympics and
central Cascades late this afternoon and evening. Otherwise, quiet
weather will continue. Clouds will increase overnight and low
temperatures will be a few degrees warmer.

Friday will be wetter as a weak/splitting front moves inland. The
coast will see rain during the morning with just a chance of rain
in the interior. Showers will mainly affect the Cascades late
Friday afternoon and evening. It will be cooler with highs only in
the upper 50s to lower 60s.

A strong upper level ridge will build over the Pac NW this weekend
for drier and warmer weather. We will probably see patchy fog
Saturday morning then skies becoming mostly sunny. Offshore flow
will increase on Sunday as a thermal trough forms along the coast.
Highs on Sunday will trend above normal with temperatures
reaching the mid to upper 70s along the coast and in the
interior...with a few low 80s possible. The cooler spots will be
along the Strait of Juan de Fuca and north interior with temps in
the 60s. 33

.LONG TERM...A strong upper level ridge will remain over the Pac
NW on Monday for one more dry and warm day. Offshore flow will
prevail with a thermal trough along the coast. This will likely be
the warmest day of the stretch with highs in the 70s to lower 80s.
A high of 78 degrees would tie the record at SeaTac.

The upper level ridge and thermal trough will shift east on
Tuesday with a return to onshore flow. This pattern change will
bring cooler marine air inland and temperatures will drop back
into the 60s. A trough over the Pac NW will bring a few showers
next Wednesday and Thursday, mainly coast, the mountains and
north part. Temperatures will trend close to normal. 33

&&

.AVIATION...Flow aloft is northerly as an upper ridge briefly
builds off the coast. Winds aloft will turn westerly late tonight
as a front approaches the coast. At the surface moderate onshore
flow this evening will turn southerly overnight. The air mass is
mostly dry and slightly unstable; it will stabilize tonight.

Skies are mostly clear except for stratus along the coast and over
the southwest interior, and some mountain cumulus. Stratus will
spread inland again Friday morning, and higher clouds will increase
as well as the front approaches.

KSEA...VFR clear this evening, with clouds all levels increasing
after 12Z Friday. Light rain is possible Friday. Southwest wind 5-10
KT tonight will increase to 10G15 KT Friday afternoon. CHB

&&

.MARINE...Onshore flow will give small craft advisory strength
westerlies in the strait this evening. A front will approach the
coast late tonight. Winds will turn more southerly and increase to
small craft advisory levels on the coast late tonight. On Friday the
advisory level winds will spread to most waters.

Winds will decrease considerably after the front passes and will
generally be light over the weekend under high pressure. Westerly
swells around 10 ft are possible on the coast starting Friday
afternoon. CHB

&&

.SEW Watches/Warnings/Advisories...
WA...None.
PZ...Small Craft Advisory from 11 PM this evening 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.

     Small Craft Advisory from 5 PM this afternoon to 2 AM PDT Friday
     for East Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 5 AM to 5 PM PDT Friday for Admiralty
     Inlet-Northern Inland Waters Including The San Juan Islands-
     Puget Sound and Hood Canal-West Entrance U.S. Waters Strait
     Of Juan De Fuca.

     Small Craft Advisory until 2 AM PDT Friday for Central U.S.
     Waters Strait Of Juan De Fuca.

&&

$$

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



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