Small Craft Advisory 248, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
330 PM PDT Sat Oct 7 2017

.SYNOPSIS...Cool, moist air streaming into Western Washington
will produce showers into tonight. The snow level will be 4000
to 4500 feet with a few inches of snow in the mountains. Sunday and
Monday should be mainly sunny. A series of upper troughs will bring
showery weather Tuesday through Friday, along with occasional sun
breaks.

&&

.SHORT TERM...Showers increasing over the area as per a look out the
window as well as a glance at the current radar. That
said...forecast looks to be very on track. With scattered cells
still out over the coastal waters as well...looks good for this kind
of activity to continue into tonight.

Models remain consistent with regards to drying things out quickly.
While the most recent ECMWF still lags about 6 hours behind the
GFS...there is agreement that the switch to northerly upper level
flow will quickly dry conditions out. That said...have cut POPs for
Sunday morning...leaving only a lingering chance for precip over the
Cascades which is all but gone by Sunday afternoon. The dry
northerly flow is the leading edge of an upper level ridge that will
traverse the area Monday...bringing dry conditions and at least
partly sunny skies.

Afternoon high temps will gradually increase over the weekend and
into the start of next week...starting off generally around 60 for
most lowland locations and peaking in the mid 60s in the interior
lowlands Monday. Like the temperatures...snow levels will follow a
similar pattern starting off around 4500 ft today...climbing into
the 5500-6500 range Sunday and peaking Monday...exceeding 8000 ft.
That said...mountains may see some accumulating snowfall with
afternoon and evening showers...but not much more for Sunday and
Monday.  SMR

.LONG TERM...An upper level trough and weakening cold front will dip
down into the area late Tuesday morning bringing the next round of
precip to W WA. In the wake of the frontal passage Wed...the trough
itself will push through allowing for POPs to persist through the
day. A secondary trough is hot on the heels of the first one
allowing for showers to return once again Thursday afternoon after a
brief lull in activity Thursday morning. Although the generally
troughy patter remains in place into Friday...conditions look
generally dry for much of the day...except for perhaps the Cascades.
Upper level ridging nudges into the area for next
Saturday...allowing for a breather in what looks to be a somewhat
active pattern.  SMR

&&

.AVIATION...The upper level trof over the region will move slowly
east tonight. Strong wly flow aloft will become nly late tonight.
Low level onshore flow will persist. Expect areas of MVFR CIGs to
become widespread late tonight. Look for brief IFR VSBYs with the
heavier showers this afternoon thru early this evening. Weakly
unstable air mass will stabilize tonight. The Olympic and Cascade
ranges will be mostly obscd.

KSEA...MVFR CIGs are expected to develop later tonight; although,
a brief period of MVFR CIGs is possible with heavy showers.
Southwest winds of 10-15 knots will diminish this evening and then
become light southerly overnight. Expect occasional gusts near 25
knots from nearby showers thru early this evening.

&&

.MARINE...
Seas will build to 11 to 17 feet on the coastal waters and to 10
or 11 feet at west entrance to the Strait of Juan de Fuca tonight.
Expect the hazardous seas to gradually subside during the day
Sunday.

Meanwhile, a 1035 mb high well offshore with lower pres east of
the Cascades will keep the flow onshore or westerly through
tonight. Expect the flow to become more northerly on Sunday and
then weaken Sunday night. Onshore or westerly flow will return on
Tuesday.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 6 PM PDT Sunday 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 for rough bar until 9 PM PDT Sunday for
     Grays Harbor Bar.

     Small Craft Advisory for hazardous seas until 6 PM PDT Sunday
     for Coastal Waters From Cape Flattery To James Island Out
     10 Nm-Coastal Waters From James Island To Point Grenville
     Out 10 Nm.

     Small Craft Advisory until 6 AM PDT Sunday for Coastal Waters
     From Point Grenville To Cape Shoalwater Out 10 Nm.

     Small Craft Advisory until 3 AM PDT Sunday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 11 PM PDT this evening for Northern
     Inland Waters Including The San Juan Islands.

     Small Craft Advisory for hazardous seas until 3 PM PDT Sunday
     for West Entrance U.S. Waters Strait Of Juan De Fuca.

&&

www.weather.gov/seattle

An illustrated version of this forecast discussion can be seen at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html