Blizzard in Alaska, December 20 to 21, 2017

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
458 AM AKST Wed Dec 20 2017

.DISCUSSION...

Models...Big picture solutions are in good agreement. As you dig
down there are differences, but mostly in timing of the waves
moving across the area today. Solutions are all in agreement when
building the ridge over the state. Good agreement continues to
around 48 hours before there are significant differences over the
Bering Sea and North Pacific. Current surface solutions
initialized well against the 20/06Z surface analysis, and they are
in good agreement through around 36 hours. Going to use mainly the
SREF for precipitation for the short term as it provides the best
solution for probabilities over the area.

Aloft...Ridging over the area last night has moved east into
Canada. A wave is moving across the interior this morning and will
move from over the Western Interior to the Eastern Interior by
around noon, and over the Yukon Territory by late afternoon.
Ridging builds over the West Coast this morning with the axis
extending from over Sand Point to Anvik to Atqasuk, moving east to
lie from southwestern Kodiak Island to Minchumina to Prudhoe Bay
and north over the Arctic before turning northwest. The ridge will
continue build tonight with 540 dam heights pushing north over
the Eastern Brooks Range and the axis lying from Valdez to Arctic
Village and north over 145W. The ridge will continue to build with
a 564 dam center developing over Yakutat as the ridge axis slides
east over the Alcan Border and north over the Arctic by Friday
afternoon with 540 dam heights extending north over the Central
and Eastern Arctic and Beaufort Sea. A series of lows will rotate
counter clockwise over Siberia with a 491 dam low 400 nm west of
Wrangel island moving west, a 493 dam low over Kamchatka moving to
200 nm west of the Gulf of Anadyr by Thursday morning and to 300
nm west of Wrangel Island by Thursday night. A 501 dam low will
move over the Western Aleutians over Adak by Thursday afternoon as
troughing digs southeast over the Central Bering Sea. At 850
hpa...With the ridge axis setting up and moving over AlCan Border
a slow warming trend is in order with some temperatures riding to
around zero with some pockets as warm as +6C over the Arctic
Saturday.

Surface...Very active pattern in the Bering Sea continues today. A
981 mb low near Point Hope will move north this morning, then turn
to the west. A 986 mb low in the West Central Bering Sea will move
to 150 nm west of St Lawrence Island this afternoon, then north
across the Chukchi Sea tonight as it weakens to 987 mb. A 1026 mb
high developing over upper Cook Inlet this morning and moving over
the Copper River Basin this afternoon at 1037 mb. A strong
pressure gradient will develop over the West Coast and Western
Interior as the low moves over St Lawrence Island today. As the
high continues to build gap winds will develop in the Alaska and
Brooks Ranges tonight and persist into Saturday. A 1036 mb high
will develop over the Upper Yukon Flats Thursday night and drift
east over the Yukon Territory Friday. Leeside troughing develops
tonight north of the Alaska and Brooks Ranges and will enhance the
gap winds, and will also enhance the Tanana Valley Jet as high
pressure builds over the Upper Tanana Valley. Gap winds and the
jet will persist into Saturday before weakening.

Arctic Coast and Brooks Range...Some clearing this morning as weak
ridge of high pressure moves across the area, then increasing
clouds by afternoon with increasing winds in the west as the low
moves through the Chukchi Sea. Will issue a Winter Storm warning
for zone 201, and extend the Winter Weather Advisory for zone 205.
No change to zone 206 advisory as winds will increase and be gusty
in the passes today and tonight. Winds on the Northwest Coast will
diminish a bit today, then increase tonight with the strongest
winds from Point Lay west. Gusts to 55 mph for Point Lay tonight,
with gusts near 80 mph at Cape Lisburne. Bands of snow will be
moving across the area with 2 to 6 inches of snow expected. Strong
winds and snow will produce blowing snow with poor visibility and
locally white out conditions may occur for a short time tonight
and Thursday on the Northwest Coast. Around Atigun Pass winds will
be gusty to around 35 mph from the south starting later today and
persisting into Thursday evening before diminishing. Temperatures
warming as the weather front moves through and there is a slight
chance of Freezing Rain on the Northwest Coast as the front passes
through. the warmer temperatures will continue through the
weekend

West Coast and Western Interior...Strong weather system moving
through the area today and tonight will produce near blizzard
conditions in most coastal areas for at least a short time.
Strongest winds will be on St Lawrence Island, the Bering Strait
Coast, Diomede, and north of Kivalina on the Chukchi Sea Coast
with gusts around 65 mph. Winter Storm Warnings remain in effect
for zones 207, 208, 209, 210, 211, 212, 213, 214, and 217. Some
snow showers this morning with a short period of clearing possible
in a few areas, then snow moving into the coast by late morning.
Snowfall will be heaviest on the southern Seward Peninsula, and
the south slopes of the Western Brooks Range. Blowing snow will
reduce visibility significantly through the day and tonight with
some areas developing white out conditions for a while tonight. As
the front moves through the area there is a slight chance of
Freezing Rain later today.

Central and Eastern Interior...Cloudy with periods of snow through
the day with up to 3 inches of snow. Heaviest snow will be north
of the Yukon River. As the high pressure builds over the area
decreasing clouds tonight. Gap winds developing tonight as the
leeside trough develops and high pressure builds in the Copper
River Basin with gusts around 55 mph near the Alaska Range Passes.
The Tanana Valley Jet also develops, but not until Thursday
afternoon, then expect east winds gusting around 50 mph in the
Delta area when it does kick in. Clearing skies in the interior
will mean colder overnight temperatures, especially in the
valleys, but with south flow aloft the hills are expected to
remain above the inversion with much warmer temperatures.

&&

Coastal Hazards for days 3 and 4...None.

&&

Extended Forecast for days 4 to 7...Models are having all kinds of
issues in the extended periods, with none of them producing
similar solutions. Will most likely use a blend of the means to
come up with a reasonable solutions for the extended forecasts.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...

Coastal Flood Advisory for AKZ211-AKZ213.

Winter Storm Warning for AKZ201-AKZ207-AKZ208-AKZ209-AKZ210-
AKZ211-AKZ212-AKZ213-AKZ214-AKZ217-AKZ218-AKZ219.

Winter Weather Advisory for AKZ205-AKZ206-AKZ221-AKZ222-AKZ225-
AKZ226.

Heavy Freezing Spray Warning for PKZ210-PKZ220.

Gale Warning for PKZ200-PKZ210-PKZ220-PKZ225-PKZ230.

Brisk Wind Advisory for PKZ215-PKZ235-PKZ240-PKZ245.

&&

SDB DEC 17