Special Marine Warning 1, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
856 PM PST Tue Jan 12 2021

.SYNOPSIS...Front moving through Western Washington early
Wednesday morning bringing an end to this round of wet weather. A
990 mb low moving into Vancouver Island early Wednesday morning
with winds increasing over the lowland for a few hours. Surface
high pressure building inland later Wednesday with an upper level
ridge building offshore will give the area a break from the wet
weather. A much weaker system will arrive Thursday night with
another weak system over the weekend.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...Evening update. Satellite
imagery has a cold front offshore. Water vapor imagery shows
developing surface low just to the northwest of Forks with an
estimated surface pressure near 990 mb. Dry slot on the imagery
shows the low will move northeast into the southern portion of
Vancouver Island and continue into the interior of Southern
British Columbia overnight. Strong pressure rises to the south
combined with the low moving inland to the north will rapidly
increase surface pressure gradients across Western Washington this
evening into early Wednesday morning. Winds will increase quickly
late this evening into the early morning hours. Have issued a
wind advisory for all of the lowlands for southwesterly winds 20
to 35 mph with gusts 40 to 50 mph. With the saturated ground it
will make it easier for the gusty winds to topple trees. Power
outages are certainly possible. The exception to this will be near
the Strait of Juan de Fuca where the winds will be westerly
overnight ( but still in the 20 to 35 mph range with gusts 40 to
50 mph ).

With the westerlies through the Strait overnight there will be a
quick strong convergence zone in Northern Snohomish county but
with the strong winds the zone will get pushed into the Cascades
quickly before daybreak Wednesday.

Previous discussion follows...
Hazards associated with this system have been outlined in detail
below:

Rain: Another round of moderate to heavy rain is expected to move
across Western Washington tonight into Wednesday morning. Additional
rainfall amounts of half an inch to an inch are expected across
the majority of the lowlands, with locally heavier amounts of 1-2
inches possible. The threat for urban and small stream flooding
will continue into Wednesday. With snow levels starting off high,
area rivers will continue to rise--details are outlined in the
hydro section below. Given saturated soil conditions, expect the
landslide threat to continue through Wednesday.

Mountain Snow: Snow levels have climbed to 6000-7000 ft across
the region today, however are expected to plummet back down to
3000-4000 feet overnight. This will allow for rain to transition
back to snow at the passes overnight. Current snow totals remain
just shy of winter weather advisory criteria, however will need to
continue to monitor this trend on the evening and overnight
shifts. Periods of heaviest snow look to be early through late
Wednesday morning. Those with pass travel planned on Wednesday
should keep an eye on the forecast and WSDOT pass conditions
before heading out.

Coastal Flooding: The combination of high tide, an incoming low
pressure system, and strong winds could result in minor tidal
overflow, mainly for areas along the interior coast early
Wednesday morning. Gusty west winds could bring added waves on top
of the high tides to westerly facing areas along Admiralty Inlet
and San Juan Islands.

Expect precipitation to gradually taper across the region through
the afternoon and evening hours. Western Washington will then see
a break in the wet weather pattern on Thursday as an upper level
ridge traverses the region. Expect this break to be short- lived,
however, as a weak system is slated to move across the region
Thursday night into Friday.

.LONG TERM /SATURDAY THROUGH TUESDAY/...Previous discussion...
Guidance looks to trend drier for Saturday with upper level
ridging nudging its way back into Pacific Northwest. Another quick
shot of precipitation looks to move across the region with a weak
disturbance on Sunday. Ensembles then hint at ridging remaining
the dominant influence across the region into early next week,
with some weak systems possibly brushing Western Washington in
northwesterly flow aloft. Have maintained a chance of POPs in the
forecast for early next week for now, but will need to see how
this trend continues over the coming days. 14 &&

&&

.AVIATION...A front will push inland tonight and early Wednesday
morning with west to southwest flow aloft. Surface wind overnight
will increase area wide, with the highest speeds anticipated along
the coast and north interior. Gusts in these areas may approach 45
mph. Other locations could see gusts between 35 and 40 mph. The
westerly push behind the front could result in a lingering
convergence zone over the King/Snohomish County line, before easing
up Wednesday afternoon. Moisture and low clouds will decrease
quickly behind the front Wednesday morning.

KSEA...Low clouds and rain through at least 12Z. Southwesterly winds
are expected to pick up at the terminal this evening. Sustained
surface winds could range from 20 to 25 knots with gusts between 30
to 35 knots through mid morning Wednesday. Wind speeds seem to slow
down considerably by Wednesday afternoon. Ceilings should lift and
break up Wednesday morning behind the front.

Kristell

&&

.MARINE...A front will push inland tonight and Wednesday morning.
Small craft advisory strength winds are likely most waters
through Wednesday. Gale force west winds are expected for the
Central Strait of Juan de Fuca and East Entrance later tonight
into Wednesday morning. Seas 16 to 20 feet over the Coastal
Waters and West Entrance Strait of Juan de Fuca will subside later
tonight through Wednesday night.

A second front will cross the area later Thursday and Thursday
night with another round of small craft advisory strength winds
most waters. High pressure will move over the area Friday. A
third, relatively weak front will cross the area around Saturday
night. Schneider/Kristell

&&

.HYDROLOGY...Cold front moving through Wednesday morning with cold
air moving in quickly behind the front. Snow levels tonight in the
6000-7000 foot range lowering down to 2500 feet Wednesday. Another
1 to 1.5 inches of rain in the mountains overnight. Precipitation
rates will decrease rapidly after 12z Wednesday. With the
decreasing rain rates Wednesday likely no additional rivers will
be added to the list of rivers with flood warnings in effect
overnight into Wednesday. Currently flood warnings are in effect
for portions of the following rivers, Snoqualmie, Chehalis,
Skookumchuck, Cowlitz, Skokomish, Satsop and Tolt rivers. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch through Wednesday evening for Admiralty Inlet Area-
     Bellevue and Vicinity-Bremerton and Vicinity-Cascades of
     Pierce and Lewis Counties-Cascades of Snohomish and King
     Counties-Cascades of Whatcom and Skagit Counties-Central
     Coast-East Puget Sound Lowlands-Eastern Strait of Juan de
     Fuca-Everett and Vicinity-Hood Canal Area-Lower Chehalis
     Valley Area-North Coast-Olympics-San Juan County-Seattle
     and Vicinity-Southwest Interior-Tacoma Area-Western Skagit
     County-Western Strait of Juan De Fuca-Western Whatcom
     County.

     Wind Advisory until 6 AM PST Wednesday for Admiralty Inlet Area-
     Bellevue and Vicinity-Bremerton and Vicinity-Central Coast-
     Eastern Strait of Juan de Fuca-Everett and Vicinity-Hood
     Canal Area-Lower Chehalis Valley Area-North Coast-San Juan
     County-Seattle and Vicinity-Southwest Interior-Tacoma Area-
     Western Skagit County-Western Strait of Juan De Fuca-
     Western Whatcom County.

     Coastal Flood Advisory from 2 AM to 10 AM PST Wednesday for
     Admiralty Inlet Area-Bremerton and Vicinity-Everett and
     Vicinity-Hood Canal Area-San Juan County-Seattle and
     Vicinity-Southwest Interior-Tacoma Area-Western Skagit
     County-Western Whatcom County.

PZ...Small Craft Advisory until 3 PM PST Wednesday for Grays Harbor
     Bar.

     Small Craft Advisory until 11 PM PST this evening 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 from noon Wednesday to 4 AM PST Thursday
     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.

     Gale Warning from midnight tonight to noon 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-West Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 10 PM PST this evening for East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning until noon PST Wednesday for Central U.S. Waters
     Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory until midnight PST tonight for Admiralty
     Inlet-Northern Inland Waters Including The San Juan Islands-
     Puget Sound and Hood Canal-West Entrance U.S. Waters Strait
     Of Juan De Fuca.

     Small Craft Advisory from 6 AM to 6 PM PST Wednesday for
     Admiralty Inlet-Northern Inland Waters Including The San
     Juan Islands.

     Gale Warning from midnight tonight to 6 AM PST Wednesday for
     Northern Inland Waters Including The San Juan Islands-Puget
     Sound and Hood Canal.

     Small Craft Advisory from 6 AM to 4 PM PST Wednesday for Puget
     Sound and Hood Canal.

&&

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