Small Craft Advisory 8, NWS Seattle, WA

Area Forecast Discussion
National Weather Service Seattle WA
242 PM PST Sun Jan 12 2020

.SYNOPSIS...Fraser outflow will increase tonight with cold air
and snow pushing south. Snow will taper on Monday but cold air
will remain over the region for several days. A weather system
arriving Wednesday night or Thursday could bring snow to the
lowlands. Warmer rainy weather is likely by next weekend.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...Fraser outflow will
begin to spill modified arctic air into Western Washington from
the north this evening. Rain showers will transition to snow from
north to south as the Fraser outflow develops. There will likely
be an area of convergence along the leading edge of the outflow
and cold air, locally enhancing precipitation and perhaps bringing
a quick burst of snow to some locations. Snow levels will fall to
sea level tonight as the cold air works its way into Western
Washington.

For now, the best estimate is most areas will see trace to an
inch or two of new snow by Monday morning but locally higher
amounts are certainly possible if some sort of convergence sets
up. Higher amounts are likely over the Eastern Strait where
upslope northeast winds will likely enhance snow accumulations and
over the East Puget Sound Lowlands closer to the Cascades.

There will also be a period of locally very windy conditions
tonight into Monday for the Northwest Interior with strong Fraser
outflow. High wind warnings are in effect for this. The
combination of wind and cold will also produce wind chills down
to near zero at times. There could be some reduced visibilities
due to blowing snow depending on how much snow falls tonight.
Winds will remain blustery from the northeast Tuesday and
Wednesday but probably not high wind.

Last but not least, heavy snow over the Cascades will end later
tonight as the weather system currently pushing through the area
moves off to the east.

Drier conditions will prevail Monday and Tuesday with modified
arctic air in place. Some snow showers will probably linger on
Monday in an area of weak convergence over the central Sound and
in continued upslope flow over the Eastern Strait but
accumulations, if any, should be light and not impactful. Some
light snow will also probably linger over Lewis county and over
the Cascades but again nothing significant is expected.

Temperatures Monday will be cold with highs struggling to reach
freezing for most of the area and highs only in the lower to mid
20s for the north interior. Lows Monday night will be mostly 15-25
with the coldest readings in the north interior. Windy Fraser
outflow will make it feel even colder for the north interior with
winds chills down to near zero.

Tuesday and Wednesday should be mostly dry with the storm track
to the south. The main story will be continued cold temperatures.
Fraser outflow will continue. Temperatures will be similar to
Monday which is to say well below normal. A weather system could
arrive late Wednesday, bringing a renewed threat of lowland snow.
Schneider

.LONG TERM /THURSDAY THROUGH SUNDAY/...A weather system will push
inland on Thursday. It should be cold enough for snow to near sea
level with this system. Amounts are highly uncertain this far out
but ensembles seem to be trending lower for what that is worth.

A wetter and warmer system will move through the area Friday or
Saturday. Precipitation should start out as snow but eventually
transition to rain as warmer Pacific air moves into the area. It's
far too early to pin down amounts or timing details but it can at
least be said there is the potential for impactful snow Friday or
Friday night. Yet another frontal system will bring more wet
weather on Sunday. The lowland snow threat should be long gone by
this time.

It should also be noted the mountains will pick up quite a bit of
snow during this period. Snow levels will rise by the weekend but
remain at or below pass level. Schneider

&&

.AVIATION...Scattered showers remain in the vicinity of most TAF
sites this afternoon, with the development of a convergence zone a
few hours ago, of which the remains of it reside across the
King/Snohomish Co border. PAE is the only airfield in close enough
proximity of this zone to be affected, elsewhere mainly scattered
showers are seen in the vicinity. Some temporary clearing has also
taken place across the South Sound.

Still expecting strong winds out of the Fraser River Valley to push
into the area this evening and overnight. Winds should shift to the
NE and become gusty at BLI first and gradually make progress south.
Scattered showers will remain and as colder air builds in, these
should change to snow. Some snow accumulation is still possible from
OLM to BLI and over to CLM later tonight/overnight. Cigs will likely
fall and remain in the MVFR category, with perhaps pockets of IFR.
Winds will be breezy out of the south into Monday (except BLI) 10-
15kts with gusts 20-30kts

KSEA...Temporary clearing and a return to VFR conditions this
afternoon are expected to be short lived as a weather system passes
through and an arctic front slides south. Dominant cig category
tonight and Monday will be MVFR. Scattered rain showers will mix
with snow and eventually turn to all snow, with light accumulation
possible (tho still possible there will be no snow). Winds S 10-
15kts gusts 20-30kts. Winds shift to the N Monday morning around
10kts.

Kovacik

&&

.MARINE...Strong pressure gradients will yield strong winds through
tonight as low pressure slides across the PacNW and high pressure
resides across Canada. Winds have been a bit slow to pick up this
afternoon across the N Inland Waters from the Fraser River Valley,
but this has certainly not been the case down the Strait of Juan de
Fuca where strong gale force winds out of the west continue this
afternoon. These winds have yielded a Convergence Zone that has slid
southward towards the Seattle metro area. Expect these strong west
winds down the Strait to continue until the NE winds barrel down
from the Fraser River Valley. Still expect this to commence by the
evening and continue overnight. Gale Warnings will remain in place
for all waters except Puget Sound, with winds gradually easing back
down to SCA levels on Monday.

As winds pick up out of the NE into far northern Wa/N Inland Waters,
expect colder air to move in and precip type to change to snow. Snow
combined with wind over the waters will likely yield blowing snow
and reductions to visibility at times. In addition, freezing spray
is not entirely out of the question, but confidence remains low in
regards to water temperatures being cold enough and conditions being
widespread enough for an advisory.

In addition to the winds, swells will increase across the offshore
waters into the 18-20 foot range. Right now think largest swell will
remain across the outer coastal waters. Surf will be rough, but will
fall under advisory criteria. Will keep a watch on this through the
evening and overnight hours.

Active marine weather looks to continue through much of the upcoming
week.

Kovacik

&&

.HYDROLOGY...River flooding is unlikely for the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 6 AM PST Monday for Bellevue and
     Vicinity-Bremerton and Vicinity-Everett and Vicinity-Hood
     Canal Area-Seattle and Vicinity-Southwest Interior-Tacoma
     Area.

     Winter Storm Warning until 3 AM PST Monday for Cascades of
     Pierce and Lewis Counties-Cascades of Snohomish and King
     Counties-Cascades of Whatcom and Skagit Counties-San Juan
     County-Western Skagit County-Western Whatcom County.

     High Wind Warning until 7 AM PST Monday for San Juan County-
     Western Whatcom County.

     Wind Advisory until 7 AM PST Monday for Western Skagit County.

     Winter Storm Warning until 6 AM PST Monday for Admiralty Inlet
     Area-East Puget Sound Lowlands-Eastern Strait of Juan de
     Fuca.

     Wind Advisory until 10 PM PST this evening for Central Coast-
     North Coast.

PZ...Small Craft Advisory until 10 AM PST Monday for Grays Harbor Bar.

     Small Craft Advisory from midnight tonight to 10 PM PST Monday
     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 midnight PST tonight 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 10 AM to 10 PM PST Monday for
     Admiralty Inlet-East Entrance U.S. Waters Strait Of Juan De
     Fuca-Northern Inland Waters Including The San Juan Islands.

     Gale Warning until 10 AM PST Monday for Admiralty Inlet-East
     Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
     Waters Including The San Juan Islands.

     Small Craft Advisory until 10 PM PST Monday for Central U.S.
     Waters Strait Of Juan De Fuca-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Gale Warning until 4 PM PST this afternoon for Central U.S.
     Waters Strait Of Juan De Fuca-West Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory until 10 PM PST Monday for Puget Sound and
     Hood Canal.

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