Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 122135
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
235 PM PDT Thu Oct 12 2017

.SYNOPSIS...Cool showery weather will give way to high pressure over
the weekend. A weak warm front will brush the north coast on Saturday
but otherwise the high pressure will keep weather systems deflected
to the north through Monday. Starting around Tuesday, fronts will
give the region some periods of wet and blustery weather.

&&

.SHORT TERM...We should see a thunderstorm or two over Southwest WA
this afternoon or early evening--around 215pm there were a few cloud
flashes off Grayland from a little storm. Showery cool weather will
continue through Friday as the coolest air aloft moves over the
region--it will be down around -12c at 700mb, the air will be
unstable.
A little shortwave enhanced the shower activity today, but behind
this weather disturbance the showers will become more scattered
again with breaks in the clouds through Friday. A PSCZ will probably
form overnight and might be over the Seattle metro area for the
morning commute. That PSCZ could give the main Cascade passes
several inch of snow Friday morning and the snow level will stay
fairly low in the mountains til weak high pressure builds for the
weekend. A winter weather advisory is still up for the south part of
the Cascades where the heavier showers have been falling today.
A weak warm front will brush the north coast of Washington Saturday
and then lift north.

.LONG TERM...Two or three frontal systems will affect the region next
week. The ECMWF is wetter with the system on Tuesday while the 12z
GFS fizzled that one out before it does much. Both models agree on a
wet blustery system midweek and perhaps another decent front around
the end of the week.

&&

.HYDRO...If the 12z GFS is right heavy rain will fall in the Olympics
Wednesday morning, but flooding is unlikely as the weather pattern
is forecast to be progressive with fronts clipping through the
region pretty quick.

&&

.AVIATION...An upper level trough is over the Pac NW today. The
air mass over Western WA is moist and unstable with showers over the
region. The flow aloft is westerly. Ceilings are a mixed bag but
mainly in MVFR range. Showers will continue to mainly impact the
interior and Cascades tonight as the trough axis moves east of the
crest. MVFR to IFR conditions will likely persist through Friday
morning. The air mass will dry out Friday afternoon with NW flow as
the trough pushes farther east and inland. 33

KSEA...Showers will remain in the vicinity this evening. S winds at
the surface to 10 kt. MVFR conditions likely through Friday morning.
33

&&

.MARINE...Northwest flow will increase tonight as low pressure
moves inland - a Small Craft Advisory is in effect for the Coastal
Waters. Winds will ease late Friday afternoon. A weak front may
brush the coastal waters Saturday. High pressure will temporarily
build over the area Sunday with a lull in wind. A stronger Pacific
system will approach and move inland next Tuesday and Wednesday. 33

&&

.CLIMATE...The daily snowfall record at Paradise is 11 inches for
today`s date and is 8 inches on 10/13. Both records were set in 1968-
-part of a 6 day stretch between the 10th and 15th 1968 when
Paradise got a little over 5 feet of new snow! Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 5 AM PDT Friday for Cascades of
     Pierce and Lewis Counties.

PZ...Small Craft Advisory until 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.

&&

$$

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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