High Wind in Washington, January 10 to 11, 2017

Area Forecast Discussion
National Weather Service Seattle WA
915 AM PST Tue Jan 10 2017

.SYNOPSIS...A weak weather system will bring mainly light rain to
southern Western Washington this morning. A cold air mass will
arrive from the north this afternoon, bring mainly clear skies and
cold weather Wednesday and Thursday. Some warming will begin Friday
and by late in the weekend temperatures will return to seasonal
norms. Next week looks warmer and wetter.

&&

.SHORT TERM...What had been reasonably good consensus in the models
regarding snow in the south interior turned out to be simply wrong.
Temperatures remained above freezing all night and are still in the
mid 30s. Nearly all precipitation has been in the form of rain; the
snow level is probably 500-1000 feet over the south. Have canceled
the snow advisory, except for the south Cascades, and updated the
forecast with rain and snow instead of snow and a higher snow level.

Colder air has trickled into the north. Temperatures over the north
interior are in the low 30s and there have been some snow flurries
there. These should be short lived as clearing from the north gets
under way. One exception could be the Strait of Juan De Fuca area
where upslope conditions could give a little snow today. Elsewhere
rain should taper in the afternoon and end tonight. Highs are not
likely to get much higher than current temperatures.

The northern edge of precipitation associated with a Pacific frontal
system moving inland to the south tonight could spread into the
south part of the forecast area tonight and Wednesday. It would be
light, and fall mainly as non-accumulation snow flurries. The air
mass will be drier from around the Puget Sound region northward,
with partly to mostly sunny skies on Wednesday. Lows tonight
should be in the 20s with highs Wednesday in the lower to mid 30s.

Dry northerly flow aloft will develop Wednesday night and Thursday,
ahead of an offshore upper ridge. Lows Wednesday night should be in
the upper teens and 20s, with highs Thursday in the lower to mid
30s. Burke/McDonnal

.LONG TERM...Previous discussion...The offshore upper ridge should
weaken and move inland on Friday for a dry, partly sunny, and
slightly warmer day. A weak front will brush our area Saturday as it
moves over the north side of the ridge into British Columbia, and a
somewhat stronger warm front will probably bring rain on Sunday with
the snow level 3000 to 4500 ft. Monday also looks wet and relatively
mild. McDonnal

&&

.AVIATION...A sharp upper level trough over the coastal waters
will close off into an upper low and drop into west-central Oregon
on Wednesday. Surface low pressure well off the northern
California coast will move into northwestern Oregon late tonight
and Wednesday. Strong high pressure over south-central British
Columbia will move slowly southeast toward eastern Washington late
Wednesday. The air mass is moist and stable, and will gradually
dry this afternoon and tonight. The exception will be far southern
portions of the interior later tonight and Wednesday (south of
KOLM) where the northern edge of the precipitation and cloud
shield associated with the low moving into western Oregon will
move in.

MVFR and local IFR are seen this morning from about KPAE-KCLM
southward, mainly in light drizzle or rain, and low cigs. Some
local light snow is occurring on the north slopes of the
Olympics at KCLM. Cold and dry air is filtering in from the
north, so expect conditions to gradually become good VFR from the
north today through this evening. Some light snow and MVFR
conditions are possible late tonight into Wednesday morning from
about KCLS southward in the south interior as a low pressure
system moves into northern Oregon. Albrecht

KSEA...Clouds and occasional light drizzle or rain with a few
snowflakes mixed in at times will gradually dry out during 18Z-
22Z. North winds 8 to 12 knots will increase to 12 to 14 knots
after 22Z. Albrecht

&&

.MARINE...A 1028 mb high over south-central British Columbia will
gradually drop southward into eastern Washington Wednesday night
and Thursday. A 995 mb low well off the northern California coast
will move into west-central Oregon late tonight then will slowly
fill as it lifts into northwestern Oregon Wednesday afternoon.
Strong offshore flow and Fraser outflow will continue through
tonight then will gradually relax on Wednesday. Light offshore
flow is expected Wednesday night through Friday. Southeasterly
pressure gradients may increase somewhat on Saturday as a weak
front approaches the area from the northwest.

Gale warnings continue over the northern 2/3 of the coastal
waters, the western 2/3 of the Strait of Juan De Fuca, and the
northern inland waters for the combination of the Fraser outflow
and strong offshore pressure gradients. Small craft advisories are
in effect for the remaining waters -except for Admiralty Inlet.
Warnings and advisories will gradually end Wednesday as pressure
gradients relax. Albrecht

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 1 PM PST this afternoon for
     Cascades of Pierce and Lewis Counties.

     Wind Advisory until midnight PST tonight for San Juan County-
     Western Whatcom County.

PZ...Small Craft Advisory until 3 AM PST Wednesday for 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.

     Gale Warning until 3 AM PST Wednesday for 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-Northern Inland Waters
     Including The San Juan Islands-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory from noon today to 9 AM PST Wednesday for
     Puget Sound and Hood Canal.

&&

www.weather.gov/seattle

You can see an illustrated version of this discussion at
www.weather.gov/seattle/gafd/latest_webafd.html