Small Craft Advisory 284, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
303 PM PST Thu Nov 24 2016

.SYNOPSIS...Rain and heavy mountain snow will continue across
Western Washington tonight. There will be a break in the weather
Friday, with an upper trough bringing more rain and mountain snow
Saturday. Another break in the weather is likely Sunday, with the
next front bringing more wet weather Sunday night and Monday.

&&

.SHORT TERM...Rain and heavy mountain snow continues tonight. A
second wave will swing up the coast tonight with more moisture
slamming into Western WA. We should see another 1-1.50" of liquid
over the mountains for more heavy snow. Snow levels are around
3000 ft. The Winter Storm Warning for the Olympics and west
slopes of the Cascades will continue as planned with new snowfall
totals up to 12". It's been a rain/snow mix at Snoqualmie but
could see an additional 3-6" of new snow there. We should see a
break late tonight/early Friday around 12z as this wave exits.

This second system will bring rising winds tonight between 9pm
and midnight...although winds seem like they will be sub-
advisory. South winds to 15 to 30 mph with local gusts to 40-45
mph seem reasonable, including the Puget Sound area.

Friday is looking less active as an upper level trough digs
offshore. We will still see a few showers across Western
Washington but heavy accumulations are not expected. The trough
will shift inland on Saturday for a return of cool, showery
conditions. Snow levels will remain low (2500-3000 feet) with a
few more inches of snow in the mountains.

Drier weather is forecast on Sunday as an upper level ridge nudges
inland. But a cool, north flow will cut temperatures down a few
degrees. An upper level short wave trough will clip through W WA
Sunday night for another batch of showers and mountain snow. 33

.LONG TERM...Showers will linger into Monday with NW flow
aloft...mainly impacting the Cascades. We may see another break as
we move into Tuesday as another ridge moves in. But the pattern
quickly turns wet and showery Tuesday night and Wednesday as a
trough kicks the ridge inland. High pressure may bring another
break in the weather toward the end of next week. 33

&&

.AVIATION...A stationary frontal system sits from the Cascades of
Whatcom County to around KHQM this afternoon. A wave developing
on the front well west of the central Oregon coast will move
rapidly northeast across the area tonight. Strong southwest flow
aloft. The air mass is moist and somewhat stable, and will remain
moist but become somewhat unstable Friday morning.

VFR conditions prevail late this afternoon with the exception of
the south coast and far south interior where rain is reducing
ceilings and visibilities to the MVFR category. Conditions will
deteriorate from the south to MVFR early this evening as the wave
of low pressure well southwest of the area approaches and rainfall
rates increase. Conditions will improve from the south Friday
morning as the air mass destabilizes somewhat and precipitation
tapers to showers. Albrecht

KSEA...The discussion above applies. Expect south to southeast wind
7 to 12 knots this evening to become south 12 to 18 knots with
gusts to 25 knots 08Z to 14Z. Winds will ease to south 6-9 kt Fri
morning. Winds at 5000 feet of SW 40 kt will become S 50-70 kt
04Z-08Z as the wave of low pres passes. Winds at 2500 ft will rise
to 50 kt as the wave of low pres passes. Albrecht

&&

.MARINE...A stationary front sits over the inland waters this
afternoon. A wave of low pressure moving northeast along the front
will pass through the waters tonight. Small craft advisories are
up for all waters except for the central portions of the Strait of
Juan de Fuca. The small craft advisories on the coast and at the
west entrance to the Strait of Juan de Fuca are for a combination
of wind and seas. Over the inland waters the small craft
advisories are for wind.

Weaker systems will affect the area Friday through the weekend.
The best chance of small craft advisory conditions will be over
the coastal waters and at the west entrance to the Strait of Juan
de Fuca. .

A vigorous frontal system will move through the area from the
northwest Sunday night. Seas will possibly build to 15 to 20 feet
behind this front as northwesterly winds increase to 30 knots from
the coastal waters to the waters off of Vancouver Island. Albrecht

&&

.HYDROLOGY...Rains from a front moving through the area pushed the
Skokomish river above flood stage. The river will likely crest
tonight and slowly recede Friday, remaining above flood stage
until early Saturday morning.

Elsewhere, flooding is not expected during the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Warning until 4 AM PST Friday for Cascades of
     Pierce and Lewis Counties-Cascades of Snohomish and King
     Counties-Cascades of Whatcom and Skagit Counties-Olympics.

PZ...Small Craft Advisory for rough bar until 3 AM PST Saturday for
     Grays Harbor Bar.

     Small Craft Advisory until 3 AM PST Saturday 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-West Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory until 6 AM PST Friday for Admiralty Inlet-
     Northern Inland Waters Including The San Juan Islands-Puget
     Sound and Hood Canal.

     Small Craft Advisory until 6 AM PST Friday for 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.weather.gov/seattle/gafd/latest_webafd.html