Flood Watch 18, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
936 AM PST Tue Nov 22 2016

.SYNOPSIS...Rain will spread across Western Washington today as a
cold front moves inland. Wet and windy weather is expected
Thanksgiving Day through the holiday weekend with heavy snow
possible in the mountains.

&&

.SHORT TERM...A cold front is on the coast this morning and will
slowly shift inland through the day. This will bring rain to much
of the area with 1-2" on the coast and Olympics and 0.25-1" in
the interior. It's also windy in the north interior with S/SE
gusts to 45 mph - a Wind Advisory is in effect. The air mass will
remain cool and unstable tonight as a deep upper level trough
moves overhead. The infrared satellite looks very cellular with
convective clouds. There is a chance of thunderstorms over the
coastal waters as this activity moves closer in. The cooler air
mass will also knock snow levels down in the mountains. Snow
levels will drop to around 2500-3000 ft in the Cascades with 1-4"
of snow possible in the passes. Wednesday will remain cool and
showery as the upper level trough remains over the region.

A strong frontal system will bring another round of wet and windy
weather Wednesday night into Thanksgiving Day. Strong winds are
possible in the north interior and a High Wind Watch is in effect.
And the Cascades passes will see more snow as snow levels will
remain low - another 2-6" of snow possible. This may make travel
over the Cascades difficult.

A third vigorous system is slated to impact the region Thursday
night into Friday. This system may bring high wind, especially
along the coast, although models are having some trouble with the
tracking and strength of the surface low. More snow will pile up
in the mountains...approaching 8-12" in the passes with 2-4 feet
at the higher peaks. Temperatures will remain near to slightly
cooler than normal through the period. 33

.LONG TERM...Previous discussion...Another weather system will
reach the area Saturday although it looks like the brunt of the
rain and wind will move onshore to the south of the forecast area.
After a break on Sunday, yet another front will bring more rain
Sunday night with decreasing showers Monday. Schneider

&&

.AVIATION...A strong occluded front over the coastal waters
will move slowly inland today. Rain slowly moving east will spread
over the interior by early afternoon. VFR conditions still with CIGS
generally 5000 feet or higher. CIGS are expected to gradually lower
this afternoon and this evening as rain continues. However, CIGS in
most areas should remain VFR 4000-5000 feet through 02Z. MVFR
conditions are expected to finally develop after 04Z.

The front will raise gusty surface winds over the coast and north
interior through early evening.

KSEA...VFR through 00Z with CIGS around 5000 feet. Rain from the
front should reach the terminal around 21Z. CIGS should drop below
5000 feet after 00Z with MVFR CIGS eventually developing after 04Z.
Surface winds will remain S-SE 6-14 KT.

&&

.MARINE...A strong occluded front over the coastal waters will move
slowly inland today. The front will crawl inland today which will
prolong the period of windy weather. The winds are expected to ease
slowly late today as the front weakens over the area.

After a short break on Wednesday with surface trough over the
coastal waters and moderate S-SW flow, another stronger occluded
front will approach the region Wednesday afternoon and evening. The
front should reach the WA coast around midnight then will move
slowly inland through Thursday morning.

Models have been showing a surface low racing NE along the front
then moving across W WA late Thursday night. The GFS and ECMWF
models have yet to reach agreement on the strength, track, and
timing of this low so confidence is lacking.

&&

.HYDROLOGY...Flooding is not expected during the next 7 days,
with the possible exception of minor flooding on the Skokomish
River.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Wind Advisory until 6 PM PST this evening for San Juan County-
     Western Whatcom County-Western Skagit-Admiralty Inlet Area.

     High Wind Watch from Wednesday evening through Thursday
     afternoon for Admiralty Inlet Area-San Juan County-Western
     Skagit County-Western Whatcom County.

PZ...Gale Watch from Wednesday afternoon through Thursday morning 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 until 4 PM PST Wednesday 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.

     Gale Warning until 10 AM PST this morning 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 for rough bar until 6 AM PST Wednesday for
     Grays Harbor Bar.

     Gale Watch from Wednesday afternoon through Thursday afternoon
     for East Entrance U.S. Waters Strait Of Juan De Fuca-
     Northern Inland Waters Including The San Juan Islands.

     Gale Warning until 6 PM PST this evening for East Entrance U.S.
     Waters Strait Of Juan De Fuca-Northern Inland Waters
     Including The San Juan Islands.

     Small Craft Advisory until 1 PM PST this afternoon for West
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 7 PM PST this evening for Central
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 6 PM PST this evening for Admiralty
     Inlet.

&&

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