Heavy Snow in Washington, April 7 to 8, 2021

Area Forecast Discussion
National Weather Service Seattle WA
810 AM PDT Wed Apr 7 2021

.UPDATE /0830 AM MORNING UPDATE/...Rain is beginning to move into
the Western Washington area this Wednesday morning, this rain will
continue through the day but will be fairly light. This weather
system will also bring mountain snow, with 8-12 inches of snow at
the passes falling between now and Thursday morning. Highest snow
totals will likely be at the Stevens Pass area as the convergence
zone will set up behind the front and allow for some
additional precipitation. The overall forecast remains on track
and the previous discussion with updated marine section is as
follows.

Butwin

&&

.SYNOPSIS...A pair of early spring storms will bring rain and
mountain snow to the region today through Saturday, along with
cooler temperatures. High pressure will lead to warmer and drier
weather through early next week.

&&

.SHORT TERM /TODAY THROUGH FRIDAY/...A pattern change will bring
cooler weather to the region today with rain and mountain snow
expected. The main impact will be accumulating snow in the
Cascades and highway passes - a Winter Weather Advisory is in
effect. Snow levels will lower to around 1500-2000 feet tonight
with snow expected at all highway passes. Down in the lowlands,
rain will start at the coast this morning then spread into the
interior this afternoon and evening. Seattle may see some rain
shadowing with westerly winds off the Olympics. The clouds, rain
and cooler air mass will keep temperatures below normal with highs
near 50 degrees. Rain and mountain snow will taper off early
Thursday as this system departs.

We'll see a 24-hour break in the weather Thursday afternoon
through Friday afternoon, then more rain and mountain snow is
expected Friday night and Saturday. This next incoming system is
cooler and snow levels will remain low. This means more
accumulating snow with impacts possible at the Cascade passes.
It's likely we'll see another Winter Weather Advisory for the
Cascades over this period. Lowlands will see between a 0.10-0.25"
rainfall with this system with higher amounts at the coast.

33

.LONG TERM /SATURDAY THROUGH TUESDAY/...Showers will linger
through Saturday morning and snow levels will remain low (around
1000 ft). A rain/snow mix is possible in the lowlands, especially
areas near the mountains, but significant accumulations are not
expected. Expect drier conditions toward the afternoon with temps
still below normal.

High pressure and offshore flow will bring dry and warmer
conditions Sunday through early next week, with temps back in the
60s Monday and Tuesday.

33

&&

.AVIATION...Westerly flow aloft becoming northwesterly tonight.
Northwesterly flow aloft Thursday. Front moving through the area
later today with increasing low level onshore flow behind the
front tonight.

Ceilings in the 1000-2000 foot range with local ceilings below
1000 feet until 18z. Ceilings improving slightly behind front
late afternoon/early evening hours up to around 3000 feet except
in the convergence zone near KPAE where ceilings will remain near
1000 feet. Convergence zone moving southeast into the Cascades
before it reaches KBFI and KSEA after 06z. Southerly winds gusting
20-30 knots 18z-06z.

KSEA...Ceilings near 1000 feet improving to near 2000 feet this
afternoon and to near 3000 feet this evening. Southerly winds 4 to
8 knots increasing to 10-15 knots with gusts 20-30 knots around
18z. Winds easing after 06z.

Felton

&&

.MARINE...Today through this weekend will see two distinct periods of active
weather with strong winds and increasing seas, with the first round
today and second on Friday through early Saturday morning. Advisory
level winds expected across all waters with both systems. High
pressure will build late this weekend with flow likely becoming
offshore as a result for the start of next week.

Northwesterly swell will increase to 6 to 8 knots on Thursday
following the first front, before rising to 10 to 13 feet on
Saturday with the passage of the second system. Choppy seas will be
likely across the inland waters Wednesday night and again Friday
night due to strong winds.

Pullin

&&

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

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Weather Advisory from 8 PM this evening to 9 AM PDT
     Thursday for Cascades of Pierce and Lewis Counties-Cascades
     of Snohomish and King Counties-Cascades of Whatcom and
     Skagit Counties.

PZ...Small Craft Advisory from noon today to noon PDT Thursday 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-West Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 6 PM PDT Thursday for Central U.S.
     Waters Strait Of Juan De Fuca-East Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Small Craft Advisory from noon today to 2 AM PDT Thursday for
     Northern Inland Waters Including The San Juan Islands-Puget
     Sound and Hood Canal.

     Small Craft Advisory from 6 PM this evening to 6 AM PDT Thursday
     for Admiralty Inlet.

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www.weather.gov/seattle