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fxus66 ksew 111657 

Area forecast discussion
National Weather Service Seattle Washington
900 am PST Mon Dec 11 2017

Synopsis...a strong upper ridge will maintain dry and stagnant
conditions across most of western Washington through Wednesday,
although a weak system will dissipate over the coast Tuesday
morning. The ridge will break down by Thursday with rain returning
Thursday night and Friday. Wet weather will continue through the
weekend with strong moist flow over the area.


Short term...there is a patch of fog over the Puget Sound area, but
otherwise skies are clear this morning. The fog will dissipate
giving sunny skies this afternoon. Gradients are generally light and
so are winds, though the cross-Cascades gradient is around -12 mb
and there are gusty east winds near the Cascades. Air quality
remains in the moderate category at most locations. The air
stagnation advisory that is in effect and will be extended to 2 PM

There is little change in the forecast today with the upper level
ridge firmly in place over the area. The inversion is still intact,
with temperatures at Hurricane Ridge, Mount Baker, and Paradise on
Mount Rainier all in the 50s. The freezing level at kuil this
morning was 12,300 feet. Camp Muir, at 10,000 feet on Mount Rainier,
was 41 degrees at 8 am, which is considerably warmer than everywhere
in The Lowlands. Temperatures are well below freezing in the passes,
where cold air is flowing through from the east side. Highs today
will be in the 40s to lower 50s, except along the north coast where
downslope easterlies off the Olympics will push temperatures into
the upper 50s.

A weak system will reach the coast tonight and dissipate. Will boost
pops a bit, into the chance category for the coast and possibly the
Olympics tonight and early Tuesday morning. This weak system will
not have enough punch to bring rain to the Puget Sound area. There
will be an increase in clouds Tuesday, but skies will clear Tuesday
night as the upper level ridge strengthens again. Lows tonight
and Tuesday night will be in the mid 20s to mid 30s. Highs Tuesday
will be in the mid to upper 40s, rising to the upper 40s to mid 50s
Wednesday. Burke

Long term...previous discussion...extended models remaining
consistent with the ridge breaking down and a series of systems
moving through western Washington. Timing on the last few runs for
the first system has been a little slower than the current forecast.
Will go ahead and dry the forecast out for Thursday. With the models
showing good consistency have raised the pops into the likely or
higher category for Friday through Sunday. Rainfall amounts in the
central Puget Sound might not amount to much for the middle of
December with model solutions showing the area somewhat rain
shadowed over the weekend. Felton


Aviation...a strong ridge at the surface and aloft over eastern
Washington will slowly weaken through Tuesday morning. A weak
frontal system over the offshore waters and its associated upper
level trough will dissipate as it moves onshore tonight. Light
southerly flow aloft will become moderate southwesterly tonight
into Tuesday. The air mass is stable and dry with patchy low level
moisture in a surface inversion this morning. Mid and high level
moisture will spread onshore tonight with some low level moisture
over the coastal zones.

Observations show patchy shallow dense freezing fog around kbli
and around the Seattle Metro area. Expect whatever fog that is
around to scatter out by 19z leaving clear skies around the
region. While pressure gradients will relax somewhat tonight into
Tuesday morning, mid and high level moisture associated with the
offshore weakening front will spread inland tonight and southerly
gradients and mixing will increase. Hence expect less fog Tuesday
morning. MVFR and IFR ceilings with low level moisture from the
dissipating frontal system Tuesday morning are expected to be
confined to the northern coastal zones. Albrecht

Ksea...cameras and observations around the terminal show fog over
the water to the west and patchy fog around kbfi. Will keep the
tempo 1/2sm fzfg group in the terminal forecast until about 18z
then expect clear skies to prevail. Light southeast winds will
become more easterly tonight. Expect less chance of fog
development tonight and Tuesday morning with an increase in mid
and high level moisture and better mixing downward of dry air from
aloft. Albrecht


Marine...a 1040 mb high over eastern Washington and lower pres
offshore will result in moderate offshore flow through this
evening. East to southeast flow will decrease later tonight as a
weak frontal system now over the offshore waters dissipates as it
moves onshore. Small craft advisories continue through this
evening for the outer portions of the coastal waters, the West
Entrance to the Strait of Juan de Fuca, and the inner coastal
waters adjacent to the West Entrance to the Strait.

Light northerly offshore flow will prevail Tuesday and Wednesday.
A cold front will sweep through the waters late Thursday night
into Friday. Albrecht


Sew watches/warnings/advisories...
Washington...air stagnation advisory until noon PST today for Admiralty Inlet
area-Bellevue and vicinity-Bremerton and vicinity-east
Puget Sound lowlands-eastern Strait of Juan de Fuca-Everett
and vicinity-Hood Canal area-Seattle and vicinity-southwest
interior-Tacoma area-western Skagit County-western Whatcom

Pz...Small Craft Advisory until 9 PM PST this evening 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 until 3 PM PST this afternoon for coastal
waters from Cape Flattery to James Island out 10 nm-West
Entrance U.S. Waters Strait of Juan de Fuca.

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