Small Craft Advisory 307, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
315 PM PST Sun Dec 25 2016

.SYNOPSIS...Precipitation will reach the coast late Monday morning
and into the interior, possibly beginning as snow, by afternoon.
Windy conditions will develop late Monday, and snowfall in the
mountains will be heavy at times Monday night and Tuesday. Showers
will decrease Wednesday, then a weaker front will bring rain
Thursday. Colder air will arrive next weekend.

&&

.SHORT TERM...A few light showers are possible on the coast tonight,
but the real rain won't arrive until Monday morning. This system
will spread precipitation inland during the day Monday. Temperatures
on the cold side--30s, with dew points in the 20s--mean there could
be a little snow or rain mixed with snow at first. As southerly
winds increase, the temperatures will climb into the low 40s in the
afternoon, and precipitation will turn to all rain. Before that
happens there could be a dusting of snow or perhaps up to an inch of
accumulation in a few spots.

Winds appear strong enough Monday night for wind advisories in the
northwest interior. The bigger story will be snow in the mountains.
Moist westerly flow aloft will continue from Monday afternoon
through Wednesday morning, with the snow level not rising much
higher than 2000 feet. Heavy snow is likely in the mountains, with
perhaps 2-3 feet in the Cascades and 1-2 feet in the Olympics. A
winter storm watch is now in effect.

After the front passes around Tuesday morning, precipitation will be
more showery in the lowlands. POPs will decline from likely on
Tuesday to slight chance on Wednesday. Temperatures will be close to
normal for this time of year, with highs in the lower to mid 40s and
lows in the 30s. Burke

.LONG TERM...Models bring another system through the area late
Thursday and have likely POPs for this. Temperatures will be a few
degrees below average Friday and Saturday in a showery regime. On
Saturday night a deep upper trough will pass by to the northeast and
clip Western Washington. There could be surface outflow from the
Fraser River canyon on Sunday, though both the Euro and GFS keep
most of the cold air bottled up in Canada. If this does happen,
Sunday will be much colder and there could be snow. Burke

&&

.AVIATION...Northwesterly flow aloft will continue over W WA into
Monday. Light low level flow today and tonight before starting to
increase in advance of an approaching front Monday afternoon. Air
mass moist and generally stable.

Much improvement to cigs over the area this afternoon with generally
VFR conditions...although still some isolated locations...including
KPAE...reporting IFR with fog. Continued drying at the mid levels as
well as some drying at the lower levels will still allow for some
clouds overnight...but risk of fog will be limited to prone areas as
opposed to being as widespread as it was this morning. That
said...cigs overnight and tomorrow should remain in VFR or high end
MVFR for most of the area while prone terminals...such as
KOLM...will likely see fog once again tonight and into the morning.

KSEA...Cigs expected to continue to improve this afternoon and
evening as low level clouds continue to thin...with clouds of a mid
to high level variety expected by tonight and into tomorrow. Light
winds this afternoon and evening turning SE at 4-8 kts tonight and
into Monday before increasing to 6-12 kts Monday afternoon. SMR

&&

.MARINE...Low level northeasterly offshore flow will continue this
evening as high pressure moves over southern British
Columbia...turning east to southeasterly tonight.

A vigorous front will move through the waters later Monday and
Monday night. Have opted to upgrade inherited Gale Watches into
Warnings as well as adding precursor Small Craft Advisories to the
mix. This pertains to Coastal Waters...East Strait and Northern
Inland Waters. For remaining portions of the Strait and Admiralty
Inlet...have opted for Small Craft Advisories to run concurrent with
aforementioned Gales. Moderate to strong onshore flow behind the
front Tuesday. The low level flow will switch to offshore on
Wednesday. A weaker front will arrive on Thursday. Felton/SMR

&&

.HYDROLOGY...Flooding is unlikely over the next seven days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...

WA...Winter storm watch for the Cascades and Olympics Monday
    afternoon through Wednesday morning.

PZ...Small Craft Advisory from 4 AM to noon PST Monday for the
     Coastal Waters.

     Gale Warning from noon to 10 PM PST Monday for the Coastal
     Waters.

     Small Craft Advisory from 4 AM to 4 PM PST Monday for the
     Eastern Strait.

     Gale Warning from 4 PM to 10 PM PST Monday for the Eastern
     Strait and Northern Inland Waters.

     Small Craft Advisory from 10 AM to 4 PM PST Monday for the
     Northern Inland Waters.

     Small Craft Advisory from 10 AM Monday to 10 AM PST Tuesday for
     Admiralty Inlet...Central and West Strait.

&&

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