Strong Wind in Washington, November 13, 2020

Area Forecast Discussion
National Weather Service Seattle WA
1008 AM PST Fri Nov 13 2020

.UPDATE /THIS MORNING/...A few updates made to the forecast this
morning to account for latest trends for the rest of the day. In
wake of cold front, precipitation has turned showery with a decent
amount of clearing along the coast and around the Sound.
Atmosphere has destabilized as seen by convective nature of
showers on satellite and via SPC Mesoanalysis. Have expanded
thunder coverage in the forecast for the rest of the day to
include most of the Olympic Peninsula and Coast. Band of heavier
showers has developed over Snohomish County, pushing eastward
toward the Cascades. Small hail has been reported in embedded
cells. If this holds together, it may dump snow at a pretty good
clip at Stevens Pass. Snow will continue throughout the day at the
passes so travelers should continue to monitor WSDOT road
conditions and prepare for snow-covered roads and possible travel
delays. Gusty winds will continue across the area with gusts on
the order of 25-40 mph and a westerly push is expected down the
Strait. Remainder of forecast will be updated this afternoon.
Aviation, marine, and hydrology sections updated below.

Carpenter

&&

.SYNOPSIS...Frontal system over Western Washington will move east
this afternoon. Cool upper level trough will move into the area
behind the front. Next system arriving Saturday night with
additional fronts Monday and Tuesday and Wednesday.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...Showers continuing tonight
with the west northwesterly flow aloft creating a rain shadow
over the Central Puget Sound area. Orographic flow into the
Cascades will decrease overnight slowing the precipitation rates
down by early Saturday morning. Will leave the winter storm
warning up for the Cascades until 4 am Saturday. Possible
convergence zone tonight could end up near Stevens Pass enhancing
the snow rates at the pass.

Next system approaching the area Saturday afternoon with rain out
ahead of the system spreading over at least the western portion in
the afternoon. Parent low for the front, a deep one in the 970s
mb, well to the north in the Gulf of Alaska. Highs Saturday near
50.

Front splitting as it moves inland later Saturday night. Rain out
ahead of the front during the evening tapering off overnight. Snow
levels start off below all of the passes before warmer air arrives
late Saturday night into Sunday morning. Precipitation amounts
much less than the current frontal system with 4 to 6 inches of
new snow expected in the Central Cascades. Higher amounts over the
North Cascades with warmer air arriving there a few hours later.

Another round of showers behind the front Sunday. Snow levels
3500-4500 feet rising even higher Sunday night as a warm front
approaches from the south.

.LONG TERM /MONDAY THROUGH THURSDAY/...Extended models in better
agreement Monday with the ECMWF more in line with the previous
GFS solution of a progressive warm front. Operational ECMWF has
the warm front to the west but a majority of the ensemble members
have the front further east with higher precipitation amounts.
This matches up pretty well with the operational GFS. Current
timing has the front moving through Monday night with a little
break in the action before the trailing cold front arrives
Tuesday. Another system arriving Wednesday with yet another system
approaching Thursday. Yes, it's November in a LaNina pattern.
Felton

&&

.AVIATION...Rain is ongoing at all terminals early this morning,
and will likely continue through most of Saturday. MVFR to IFR
conditions this morning, with limited visibilities in the heaviest
rain showers. Ceilings may recover back to lower end VFR into the
afternoon as the showers become more spotty in nature. Winds are
breezy out of the south, with gusts 25-30 knots at coastal
terminals, with generally 15-25 knots elsewhere. A slight chance
for a thunderstorm exists this afternoon, mainly along the coast
and southern Puget Sound region, but will largely depend on breaks
in the cloud cover. Erratic and gusty surface winds are possible
in the vicinity of any thunderstorm that develops.

KSEA...MVFR cigs likely to persist through much of this morning,
with chances for deterioration into brief periods of IFR in the
heaviest rain showers to move over the terminal. Cigs likely to
recover back to low end VFR by this afternoon as the showers become
more scattered. Winds out of the south at 10-15 knots with gusts
between 20-25 knots expected.

Kristell/Butwin

&&

.MARINE...A low continues to push onshore into Vancouver Island this
morning, with gales continuing this morning over the coastal waters.
As the low pushes inland and the associated front pushes into the
inland waters, expect a strong push of gales through the Strait of
Juan de Fuca and much of the coastal waters. A few isolated storm
force gusts are possible, though not expected to be widespread.
Small craft advisories remain in effect for the other portions of
the waters, with the potential for a few isolated gale gusts as the
front pushes eastward.

Another deepening trough over the offshore waters will bring another
round of stronger winds late Sunday into Sunday. The current
advisory is on track, but will continue to assess the potential
strength as some guidance indicates gales could again be possible
over portions of the waters.

Meanwhile, combined seas will build this afternoon into Saturday to
16-18 ft over the coastal waters, with a mix of wind wave and fresh
swell leading to large seas over the waters. Seas will slowly
subside by Sunday, though the next system may again build seas into
the 15+ foot range. Cullen

&&

.HYDROLOGY...The Skokomish River near Potlatch has risen above
minor flood stage this morning - a flood warning has replaced the
flood watch. The river should be cresting shortly and fall below
flood stage later this evening. Additional rise is possible this
weekend with more rainfall but it should remain below flood stage.
Elsewhere, river flooding is not expected this weekend.

A wetter atmospheric river system with higher snow levels will
move through the area Monday into Tuesday. Models have trended
more progressive with the system vs stalling the warm front over
the area so this may limit the flooding threat area-wide. The
Skokomish River may see another round of flooding though. Will
continue to monitor trends.

Carpenter

&&

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

PZ...Small Craft Advisory from 1 PM Saturday to 1 AM PST Sunday 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 PM PST this evening for Admiralty Inlet-
     Central U.S. Waters Strait Of Juan De Fuca-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-East Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Small Craft Advisory until 2 AM PST Saturday for Grays Harbor
     Bar.

     Small Craft Advisory until 10 PM PST this evening for Northern
     Inland Waters Including The San Juan Islands-West Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 4 AM PST Saturday for Puget Sound and
     Hood Canal.

&&

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