Avalanche and Heavy Snow in Washington, February 8 to 9, 2019

Area Forecast Discussion
National Weather Service Seattle WA
259 AM PST Fri Feb 8 2019

.SYNOPSIS...A winter storm will affect the area today into
Saturday bringing potentially significant lowland snow to portions
of the area and strong winds to portions of the northern interior.
Additional weather systems may bring a threat for additional snow
late in the weekend into early next week.

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.SHORT TERM /TODAY THROUGH SUNDAY/...There is still only limited
evidence on satellite or radar images of the winter storm that
will affect the region later today through Saturday. But cold air
associated with a strengthening 1052 mb high over far northeastern
British Columbia can be seen to be surging southwestward into the
interior of central BC and high clouds rotating around a
developing upper low just offshore can be seen moving off the
central BC coast around Prince Rupert. Also, a few echos can be
seen to be developing over the northern coastal waters of
Washington early this morning.

Short term models continue to show rapid development of a surface
low off the northern coast midday. This low then deepens and moves
southeastward along the coast reaching near Hoquiam early this
evening. Temperatures are below freezing across the area early
this morning. Despite some low level warm air advection today,
1000-850 mb thicknesses are expected to top out at 1292-1296
meters over the coastal areas and in the mid and upper 1280 meter
range in the interior. With the increase in clouds, dewpoints in
the 20s, and a cooling column aloft, expect precipitation to start
as snow -and remain as snow- over all of the area today. Snow will
likely be heaviest this afternoon over the coastal zones, then
later this afternoon and this evening 50 miles either side of a
line form about Port Angeles to North Seattle as strong
convergence and frontogenesis occurs to the east and northeast of
the low. Snowfall rates of 1-2 inches per hour are possible
during the afternoon and evening commute around the Seattle area
leading to a very bad PM commute. Snowfall will continue continues
into early Saturday before it starts to taper off from north to
south. However, areas on the northern Olympic Peninsula from just
west of Port Angeles to Sequim will keep snow going into the day
on Saturday. Total accumulations will average 4-7 inches with
locally heavier amounts. Amounts may be heavier if snow water
ratios are higher than currently expected. A winter storm warning
is in effect From Port Angeles, Oak Harbor, and Mount Vernon
southward to the Hood Canal and Tacoma areas midday today through
midday Saturday, and Winter Weather Advisories are in effect
elsewhere. A winter weather advisory was also issued for midday
today through this evening for the north and central Washington
coast for 2-4 inches there.

Very windy conditions will develop around Bellingham and the San
Juans this evening. Windy conditions will spread westward through
the Strait to the northern coastal areas and southward through the
Puget Sound area late tonight into Saturday with windy conditions
continuing through late Saturday night or Sunday morning. Peak
winds will likely occur Saturday afternoon and evening with 50-60
mph gusts in the Fraser outflow area (the San Juan Islands,
Western Skagit County, and Western Whatcom County). Peak winds
will likely be during the day on Saturday into Saturday evening
elsewhere with areas near the shorelines of Puget Sound seeing
north winds 20-30 mph with some gusts to 45 mph. Portland to
Bellingham pressure gradients will peak at -10.5 mb per latest
models, so wind advisories may be needed for Saturday.

Conditions will dry out Saturday night into early Sunday with only
a few flurries around. Another system is expected to approach the
Washington coast and southern portions of the interior late
Sunday, so precipitation chances will increase there late in the
day and will be in the form of snow. Albrecht

.LONG TERM /MONDAY THROUGH THURSDAY/...The pattern will be one
that results in much below normal temperatures through the
upcoming week. At this time, latest models focus most of the
precipitation with systems that move into the area during the
Sunday night through Thursday period on the southern portions of
the forecast area while the northern portions remain mainly dry.
But confidence in the details of the extended forecast remains
low. Only minor changes were made to the extended forecast
tonight. Albrecht

&&

.AVIATION...North to northwesterly flow aloft will gradually turn
more westerly this afternoon and evening as an upper level low moves
southward into W WA. Mid and high clouds are in place over the area
and most terminals continue to report VFR conditions at the time of
this writing. Cigs are expected to fall once the main low starts its
approach with widespread IFR conditions expected by late this
afternoon as snow increases over the area. Outflow winds from the
Fraser River Valley will add the complication of gusty winds to some
terminals...most notably KBLI. KSEA/KBFI along with KPAE and KCLM
will see a mix of both gusty winds and moderate snowfall...impacting
visibilities. Snow is expected to taper off Saturday afternoon
although temperatures are expected to remain below freezing. A
prolonged period of subfreezing temperatures appears likely into
next week, not allowing for much melting. Additional snow could also
arrive by Monday. SMR

KSEA...Snow is expected to begin early this afternoon and may be
heavy at times through tonight. Current estimates put 1-3 inches of
snow at the terminal by late this afternoon with an additional 1-3
possible tonight. After the modified arctic front moves through
winds will shift to north and pick up-- becoming rather blustery by
daybreak Saturday. Snow showers will taper off through Saturday
morning, with up to an additional inch or two possible. Total
snowfall for Sea-Tac is expected to be about 4-6 inches. SMR

&&

.MARINE...A 998-1000 mb surface low will form off the Washington
coast today, shifting south off Astoria by this evening. High
pressure over British Columbia will create a strong north-
northeast pressure gradient over Western Washington tonight
through the weekend. Fraser outflow will likely produce Gale force
winds over the northern inland waters this evening through
Saturday. Virtually all models generate a very strong PDX- BLI
gradient near -10 mb which should prudes gales over remaining
interior waters including Puget Sound late tonight and Saturday.

Another cold system will affect the waters late Sunday and Monday an
maybe again mid week. Fraser outflow winds could still produce near
gale force winds at times in the north interior. Differences are
still evident between models, mostly affecting the extent of snow
reaching the interior. Winds due to Fraser outflow will be likely,
though not as strong as the upcoming Friday night/Saturday system.
dtm

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.HYDROLOGY...River flooding not expected in the next 7 days.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Warning from noon today to 4 PM PST Saturday for
     Admiralty Inlet Area-Bellevue and Vicinity-Bremerton and
     Vicinity-East Puget Sound Lowlands-Eastern Strait of Juan
     de Fuca-Everett and Vicinity-Hood Canal Area-Seattle and
     Vicinity-Tacoma Area-Western Skagit County.

     Winter Weather Advisory from 7 AM this morning to 4 PM PST
     Saturday for Cascades of Pierce and Lewis Counties-Cascades
     of Snohomish and King Counties-Cascades of Whatcom and
     Skagit Counties-Olympics.

     High Wind Warning from 10 PM this evening to midnight PST
     Saturday night for San Juan County-Western Skagit County-
     Western Whatcom County.

     Winter Weather Advisory from 6 AM this morning to noon PST
     Saturday for San Juan County-Western Strait of Juan De Fuca-
     Western Whatcom County.

     Winter Weather Advisory from 4 PM this afternoon to 4 PM PST
     Saturday for Lower Chehalis Valley Area-Southwest Interior.

     Winter Weather Advisory from 10 AM this morning to midnight PST
     tonight for Central Coast-North Coast.

PZ...Gale Warning from 10 PM this evening to 2 AM PST Sunday for
     Admiralty Inlet-Central U.S. Waters Strait Of Juan De Fuca-
     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-East Entrance U.S.
     Waters Strait Of Juan De Fuca-Puget Sound and Hood Canal-
     West Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning from 3 PM this afternoon to 11 AM PST Sunday for
     Northern Inland Waters Including The San Juan Islands.

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