Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 121535
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
835 AM PDT Tue Sep 12 2017

.SYNOPSIS...An upper trough along the British Columbia coast will
move slowly southeast across the region today through Thursday,
for near normal temperatures and partly to mostly sunny days. A
weak upper ridge will bring sunny and slightly warmer weather
Friday. A front and its upper trough should bring some rain to
Western Washington beginning Sunday or Sunday night.

&&

.SHORT TERM...An upper trough will be over the area today and
Wednesday with low level onshore flow. The might be a few showers
over the North Cascades but the main impact will be to bring some
clouds at times, especially night and morning hours. It does look
like low clouds will be more extensive Wednesday morning compared
to today but there should be afternoon sunshine both days. The
upper trough will sharpen and push inland Thursday with dry
northerly flow aloft developing over Western Washington. Low
level onshore flow will weaken and there should be a corresponding
decrease in morning clouds Thursday. Highs the next few days will
be near normal. Schneider

.LONG TERM...Previous discussion...Dry northerly flow will
prevail over Western Washington on Friday, following the trough
discussed above and a weak upper ridge offshore. Friday should be
mostly sunny with temperatures near normal. That ridge will
progress across the forecast area Friday night. A weak upper
trough will move through on Saturday, but all the models show dry
weather for the area. A more significant front and upper trough
will bring some precipitation to the area beginning Sunday or
Sunday night, and continuing into Monday. Models differ on timing
and other details, but they all show some precipitation over the
forecast area. The snow level will probably fall to around 7000 ft
Sunday night and Monday. McDonnal

&&

.AVIATION...There are a few areas of morning low clouds but
otherwise there are just some sct-bkn higher clouds from the weak
cold front breaking up over the area. An upper level trough will
move over the Pacific Northwest through Wednesday for strong
westerly flow aloft. Onshore flow will strengthen this afternoon and
evening so morning clouds will probably be over the area on Wed.

KSEA...A few areas of morning low clouds are drifting around and
there will be scattered clouds from a weak front breaking up over
the area. North breeze.

&&

.MARINE...A weakening cold front will move across the area this
morning. Onshore/westerly flow will strengthen behind the front as
high pressure builds over the offshore waters. The flow will ease
later tonight and Wednesday and becoming more northerly Thursday.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 6 AM PDT Wednesday for Coastal Waters
     From Cape Flattery To James Island 10 To 60 Nm-Coastal
     Waters From James Island To Point Grenville 10 To 60 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater 10
     To 60 Nm.

     Small Craft Advisory until 1 AM PDT Wednesday for Coastal Waters
     From Cape Flattery To James Island Out 10 Nm-Coastal Waters
     From James Island To Point Grenville Out 10 Nm-Coastal
     Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

     Small Craft Advisory until 2 AM PDT Wednesday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca-West 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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