Heavy Snow in Washington, February 19 to 20, 2022

Area Forecast Discussion
National Weather Service Seattle WA
844 AM PST Sat Feb 19 2022

.SYNOPSIS...Weather system will move through Western Washington
today bringing rain to the lowlands and mountain snow. A convergence
zone tonight into Sunday morning will allow for heavy mountain snow
for portions of the Cascades. An upper level trough over the area
Sunday and Monday will keep showers in the forecast along with
cooler temperatures. Upper level ridge building offshore Tuesday and
Wednesday will provide dry conditions. A weak system
expected Thursday with the ridge rebuilding Friday.

&&

.SHORT TERM /TODAY THROUGH MONDAY/...Current satellite imagery shows
low clouds in place over W WA this morning with the deck getting so
low that some locations are seeing reductions in visibility. Current
radar shows not much in the way of precip just yet, save for a patch
over portions of western Whatcom and Skagit counties. That is not to
say that precip is not occuring elsewhere, as there are a fair
amount of light echoes out there over the NW portions of the CWA,
however echoes are so light as to indicate that precip is either
extremely light or that radar is picking up the aforementioned low
cloud deck.

Cold front embedded in the northwesterly flow aloft moving through
Western Washington later this afternoon. System will be weakening as
it approaches the area with precipitation spreading over most of the
remainder of the area in the afternoon. With the northwesterly flow
aloft Central Puget Sound region will be in the rain shadow. Not a
lot of moisture associated with the front so precipitation will have
a hard time overcoming the rain shadow in the Seattle area. Heaviest
rain expected along the coast and in the North and Central Cascades.
Snow levels will be near 3000 feet with snow in all the passes this
afternoon. Highs in the mid and upper 40s.

Strong post frontal onshore flow tonight with convergence zone
developing over Snohomish county. Current data suggests the zone
will set up right over Stevens Pass and remain between Stevens and
Snoqualmie pass overnight. Could see as much as a foot of snow
overnight at Stevens Pass with a little less at Snoqualmie. Thus,
inherited headline for the Central Cascades looks good and will
remain in place. 850 mb winds west northwesterly 20-35 knots behind
the front for good orographics for the remainder of the Cascades.
Winter weather advisory for the Northern and Southern Cascades also
looks fine. Could see some small hail with the convergence zone in
Snohomish county. Showers over the remainder of the area outside the
convergence zone with upper level trough over the area. Lows in the
mid 30s to lower 40s.

Upper level trough hanging over Western Washington Sunday into
Monday keeping showers in the forecast. Low level onshore flow
weakening Sunday morning into the afternoon hours with the
convergence zone sliding south over King County before
dissipating Sunday afternoon. Another convergence zone possible
Sunday night into Monday morning. This convergence will be caused
by the increasing northerly winds in the Puget Sound running into
the southerlies from the weakening onshore flow over the southern
Puget Sound not the usual westerlies through the Strait of Juan de
Fuca. Temperatures not quite cold enough for sticking snow with
the convergence but heavier showers could put a little snow in the
air. Showers decreasing from the north Monday afternoon as the
upper level trough digs south. Air mass remaining unstable Monday
with a few showers popping up with the daytime heating over the
southern portion of the area. Highs in the mid 40s.

Air mass continuing to cool Monday night with the snow level down
to around 500 feet. Any lingering showers could be a mix of rain
and snow on the hills. Moisture will be decreasing rapidly keeping
the shower chance Monday night confined to before midnight. Felton/18

.LONG TERM /TUESDAY THROUGH FRIDAY/...From Previous
Discussion...Models in good agreement Tuesday and Wednesday with a
cool dry air mass settling in over Western Washington. High pressure
building over Southern British Columbia with Fraser River outflow
winds over the Northwest Interior easing Wednesday. Lows below
freezing Tuesday morning in most locations. Record lows possible
Wednesday morning with the colder locations dropping down into the
teens. Operational runs bringing a weak shortwave down over the area
Thursday into Thursday night. Ensembles are much weaker with this
feature with only a few solutions indicating light precipitation.
Will indicate a slight chance of showers. Temporary upper level
ridge building over the area Friday. Low temperatures remaining
below freezing Thursday morning and near freezing Friday morning.
Highs will remain well below normal, near 40 Tuesday and Wednesday (
a little cooler in Whatcom county ), lower to mid 40s Thursday and
mid to upper 40s Friday. Felton

&&

.AVIATION...A frontal system will sweep through western WA today
for showers and IFR to MVFR conditions. The flow aloft is westerly.
Post-frontal onshore flow will follow this afternoon and evening
with a convergence zone near the King/Snohomish line.
Showers will linger into Sunday morning with onshore flow and
troughing over the region. 33

KSEA...S/SW flow 10-20 kt today with MVFR cigs. A convergence zone
will be north of the terminal this evening but will shift south in
the vicinity by 06z. 33

&&

.MARINE...South to southwest flow will increase over the waters
today with a frontal system. Expect post-frontal onshore flow this
afternoon and evening with W gales through the Strait of Juan de
Fuca. Winds will ease late tonight into Sunday morning. The flow
will turn offshore Sunday and Monday with N/NE Fraser River outflow
winds increasing Monday afternoon. Offshore flow will ease on
Wednesday. High pressure will bring light winds on Thursday. 33

&&

.HYDROLOGY...No river flooding expected in the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory until 4 PM PST Sunday for Cascades of
     Pierce and Lewis Counties-Cascades of Whatcom and Skagit
     Counties.

     Winter Storm Warning until 4 PM PST Sunday for Cascades of
     Snohomish and King Counties.

PZ...Small Craft Advisory until 6 PM PST Sunday 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 PM this evening to 10 AM PST Sunday
     for Central U.S. Waters Strait Of Juan De Fuca-East
     Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning until 10 PM PST this 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 1 AM PST Sunday for Northern Inland
     Waters Including The San Juan Islands.

     Small Craft Advisory until 1 AM PST Sunday for West Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 4 PM this afternoon to 4 AM PST Sunday
     for Admiralty Inlet.

     Small Craft Advisory until 4 AM PST Sunday for Puget Sound and
     Hood Canal.

&&

www.weather.gov/seattle