Heavy Snow in Washington, January 11 to 13, 2021

Area Forecast Discussion
National Weather Service Seattle WA
238 PM PST Mon Jan 11 2021

.SYNOPSIS...An active period of weather will bring periods of
heavy rain, mountain snow, river and coastal flooding through
Wednesday. We'll see a break in the action by Thursday followed by
more showers on Friday. High pressure will bring quieter weather
over the weekend.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...We're in for another
soggy/wet 48-hr period of weather across western WA due to strong
moist flow over the region. The main impacts will be periods of
heavy rain, mountain snow, river flooding, high threat for
landslides, and strong winds. In addition, we're also seeing
possible minor tidal overflow due to king tides on Tuesday.

Today's system was the primer with a frontal system draped/stalled
over the region. Rainfall amounts were generally between
0.25-0.50" in the interior with up to 1.00" at the coast. The
Skokomish River is seeing a sharp rise and will likely cross flood
stage tonight. Up in the mountains, the passes are seeing snow
with easterly flow. More snow is expected overnight and into
Tuesday with heavy snow likely from Stevens Pass to Mount Baker
(with 1-2 feet expected). Snoqualmie Pass will likely see a
rain/snow mix for lesser amounts.

Tuesday will be our wettest period with rain essentially all day.
Snow levels will be rising in the mountains but east winds will
keep the Cascade passes near freezing for more snow. All other
rivers will start to see rises with heavier precipitation totals.
In addition, minor tidal overflow is possible with high tides and
anomalies close to the HAT (highest astronomical tide). This
would affect both the coast and Salish Sea.

Finally, our last surge of moisture will cover the region Tuesday
night into Wednesday. By then rivers will be cresting and several
rivers may be close to minor flooding. Snow levels will lower
Wednesday afternoon or evening to around 3000 ft for rain changing
back to snow in the mountains and Cascade passes. It'll be windy
through the Strait of Juan de Fuca Wednesday afternoon with a
strong push through the strait.

All in all, through Wednesday, precipitation amounts will range
from 1-2" in the interior to 2-4" around the Olympic peninsula.
This may put more pressure on our already saturated soils which
leads to an increase threat for landslides. 33

.LONG TERM /FRIDAY THROUGH MONDAY/...A break on Thursday will
bring a welcome respite thanks to high pressure crossing the area.
But more rain and mountain snow is in store for Friday as the
ridge exits and a (weak) trough moves through. High pressure may
bring a period of dry and quiet weather as we move into the
weekend, based on ensemble mean forecasts. 33

&&

.AVIATION...A front will stall over the area tonight and Tuesday
with southwest flow aloft. The air mass will be stable. There
will be a mix of low and mid clouds tonight and Tuesday with
lower ceilings generally in areas of steadier and heavier rain.

KSEA...Ceilings have popped as a front over the area has sagged
slightly to the south. Rain should increase again this afternoon
and evening and ceilings should lower as the frontal band wobbles
north and basically stalls over area. Southeast wind 7-14 knots.
Schneider

&&

.MARINE...A frontal system will stall over the area through
Tuesday with small craft advisory strength winds at times most
waters. Gale force southerly winds are expected tonight for the
Coastal Waters, East Entrance Strait of Juan de Fuca, and Northern
Inland Waters.

Onshore flow will develop early Wednesday with gale force west
winds for the central and eastern Strait. Winds will ease
Wednesday night. A weaker front will cross the area around
Thursday night with another round of small craft advisory
southerly winds most waters.

Weak high pressure will move over the area Friday and Saturday
with lighter winds.

Seas will remain above 10 feet for the Coastal Waters and West
Entrance Strait of Juan de Fuca through Wednesday. Schneider

&&

.HYDROLOGY...A series of wetter frontal systems will cross the
region with periods of heavy rain and higher snow levels into
Wednesday. National Water Model shows deep ground saturation
across the area and streamflows running above average in most
basins. Rainfall for the past 7-14 days is running some 150-300%
of normal across the area. All this combined with additional heavy
rainfall will create renewed concern for landslide threat as well
as localized urban and small stream flooding. Renewed rises
expected on rivers, area-wide. The extent of river flooding will
hinge on where the heaviest precipitation falls and how much.
Current area of focus is across the Olympic Peninsula and lowlands
from Seattle and King county southward.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Flood Watch from 10 PM PST this evening through Wednesday
     evening for Admiralty Inlet Area-Bellevue and Vicinity-
     Bremerton and Vicinity-Cascades of Pierce and Lewis
     Counties-Cascades of Snohomish and King Counties-Cascades
     of Whatcom and Skagit Counties-Central Coast-East Puget
     Sound Lowlands-Eastern Strait of Juan de Fuca-Everett and
     Vicinity-Hood Canal Area-Lower Chehalis Valley Area-North
     Coast-Olympics-San Juan County-Seattle and Vicinity-
     Southwest Interior-Tacoma Area-Western Skagit County-
     Western Strait of Juan De Fuca-Western Whatcom County.

     Coastal Flood Advisory from 3 AM to 8 AM PST Tuesday for
     Admiralty Inlet Area-Bremerton and Vicinity-Everett and
     Vicinity-Hood Canal Area-San Juan County-Seattle and
     Vicinity-Tacoma Area-Western Skagit County-Western Whatcom
     County.

     Winter Storm Warning until 4 PM PST Tuesday for Cascades of
     Snohomish and King Counties-Cascades of Whatcom and Skagit
     Counties.

     Coastal Flood Advisory from 9 AM to 3 PM PST Tuesday for Central
     Coast-Eastern Strait of Juan de Fuca-North Coast-Western
     Strait of Juan De Fuca.

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

     Gale Warning until 7 AM 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.

     Gale Warning until 6 AM PST Tuesday for East Entrance U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 7 PM PST this evening for Northern
     Inland Waters Including The San Juan Islands.

     Gale Warning from 7 PM this evening to 6 AM PST Tuesday for
     Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory until 4 AM PST Wednesday for Puget Sound
     and Hood Canal-West Entrance U.S. Waters Strait Of Juan De
     Fuca.

     Small Craft Advisory until 7 AM PST Tuesday for Central U.S.
     Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 4 AM PST Wednesday for Admiralty
     Inlet.

&&

www.weather.gov/seattle