Heavy Snow in Washington, February 15 to 17, 2021

Area Forecast Discussion
National Weather Service Seattle WA
426 AM PST Mon Feb 15 2021

.SYNOPSIS...A cold front will move through the area today with
rain in most lowland locations and snow in the mountains. Trapped
cold air in the interior of Whatcom county and in the Cascade
foothills will keep a wintery mix of precipitation this morning.
Moist northwesterly flow aloft keeping showers in the forecast
tonight through Tuesday. Weak upper level ridge moving through
Wednesday for a short dry spell. Storm track takes aim at the
Pacific Northwest late in the week through the weekend with a
series of weather systems moving through the area.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY/...Satellite imagery shows
cold front offshore early this morning. Doppler radar has
precipitation over the area. Surface observations show
temperatures above freezing except in the interior of Whatcom
county and in the foothills of the Cascades in places exposed to
easterly or northeasterly winds.

Front offshore moving through the area late in the day with rain
and mountain snow ahead of the front. Both the cross Cascade and
Bellingham to Williams Lake gradients becoming less negative this
morning. This will slowly eliminate the source of the shallow
layer of cool air near the surface as the northeast ( Whatcom
county ) and easterly ( foothills of the Cascades ) winds weaken.
Will keep a winter weather advisory up for both places for some
light snow in Whatcom county and light freezing rain ( ice
accumulations a tenth of an inch or less ) in the foothills. As
the easterlies weaken the layer of freezing rain will move up to
the approaches to the passes this afternoon. Snow continuing in
the mountains today with the higher amounts over the Central and
Southern Cascades. Highs today in the mid to upper 30s in Whatcom
county, lower 40s elsewhere.

Front moving through the area this evening with the steady
precipitation giving way to showers in the lowlands. Decent
orographics continuing in the mountains keeping steady snow going
in the Cascades. Winter weather advisory continuing for the
Central and Southern Cascades. Lows tonight will remain above
freezing, in the mid and upper 30s.

Moist northwesterly flow aloft Tuesday will keep showers in the
forecast for the lowlands. Snow continuing in the mountains. Have
extended the Winter Weather Advisory for the Central and Southern
Cascades through Tuesday at 6 pm. Highs Tuesday in the lower to
mid 40s.

Shower activity coming to an end Tuesday night as a weak upper
level ridge approaches the area. With a little clearing good
chance of some fog forming in the usual locations like the
Southwest Interior. The colder locations will bottom out near
freezing with the remainder of the area in the mid 30s.

Dry day Wednesday as upper level ridge moves through Western
Washington. Light surface gradients in the morning for a potential
low cloud deck plus increasing high level clouds in the afternoon
gives a partly sunny forecast. Highs in the mid 40s.

.LONG TERM /THURSDAY THROUGH SUNDAY/...Extended models and
ensembles in good general agreement with a system moving through
the area Thursday and another system in the Saturday/Sunday time
frame. Snow levels could be as low as 1000 feet with the onset of
the precipitation Thursday but will rise during the day. Parent
low with the system over the weekend well to the north but there
is still some decent surface gradients over the area for possible
windy conditions. The mountains will pick up a considerable amount
of snow through the period. Felton

&&

.AVIATION...A weather system will move through the area today.
West flow aloft today will become northwest tonight. At the
surface, east to southeast flow will switch to southwest to west
behind the frontal system later today. The air mass will be moist
and stable.

The threat of snow or some sort of wintery mix has mostly ended
for the lowlands. The exception will be the valleys near the
Cascades where a mix of rain, snow, and freezing rain will linger
until late this morning.

KSEA...Low clouds and occasional reduced visibilities in rain
today. Rain will taper this afternoon but low clouds will linger
into tonight. East to southeast wind 5-10 knots will switch to
south 10-15 knots late this morning. Schneider

&&

.MARINE...A frontal system will shift inland today. Small craft
advisory strength southeast winds over the Coastal Waters and East
Entrance Strait of Juan de Fuca will switch to westerly behind the
front later today. Small craft advisory strength westerly winds
will continue into Tuesday for the Coastal Waters and Strait of
Juan de Fuca with gale force west winds possible for the Central
and Eastern Strait later in the day. Onshore flow will ease on
Wednesday then another frontal system will move through the area
Wednesday night and Thursday. Schneider

&&

.HYDROLOGY...No river flooding expected in the next 7 days. The
threat for urban flooding is decreasing with the gradual
temperature rise during the day but it still can not be ruled
out with so much snow left on the ground. Felton

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 10 AM PST this morning for East
     Puget Sound Lowlands-Western Whatcom County.

     Winter Weather Advisory until 6 PM PST Tuesday for Cascades of
     Pierce and Lewis Counties-Cascades of Snohomish and King
     Counties.

PZ...Small Craft Advisory until 4 PM PST Tuesday 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 until 4 AM PST Tuesday for Grays Harbor Bar.

     Gale Watch from Tuesday morning through Tuesday evening for
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 10 AM PST Tuesday for East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 4 PM this afternoon to 4 PM PST
     Tuesday for West Entrance U.S. Waters Strait Of Juan De
     Fuca.

     Small Craft Advisory from 4 PM this afternoon to 10 AM PST
     Tuesday for Central U.S. Waters Strait Of Juan De Fuca.

&&

www.weather.gov/seattle