Ice Storm and Heavy Snow in Alaska, December 18 to 22, 2021

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
207 PM AKST Fri Dec 17 2021

.SYNOPSIS...A very active pattern will bring periods of snow to
most of the forecast area in advance of winter storm that may
bring freezing rain to the Norton Sound Region, and heavy snow to
areas from Northwest Interior to the Middle Yukon and areas east.
See latest Winter Storm Watches and Advisories for details.

&&

.DISCUSSION...

Models...17/12Z solutions are not being very cooperative today,
especially with the inbound system for Sunday to Tuesday. Current
precipitation forecast ranges from GFS around 0.25 inch to ECMWF
around 1.00 inch of liquid, with the NAM and Canadian solutions
somewhere in between. Will be leaning a bit more toward a blend of
the ECMWF/NAM/Canadian for the time being since the GFS had such a
big change the last couple of runs. Still potential for freezing
precipitation from Seward Peninsula south along the coast and in
the Nulato Hills Saturday night and Sunday as warm air surges
north. Still a slight chance of a pocket of that warm air moving
into the Interior and producing some freezing rain. Snow ratios
and QPF will continue to be a big challenge through the weekend.
Strong winds and warmer temperatures will impact the ratios on the
West Coast, while warmer temperatures in the Interior will be the
obstacle.

Aloft...At 500 hpa...Progressive pattern across the area continues
with decaying trough over the AlCan this afternoon that will move
east. A transitory ridge extends north over Kodiak City to Galena
to Kotzebue this afternoon and will move over the AlCan by late
Saturday morning. A 508 dam low has moved over St Matthew Island
with a trough extending south over Unalaska. Troughing remains
over the Arctic extending west from a 502 dam low 150 nm north of
Banks Island. Saturday morning only change over the Arctic will be
a closed low 300 nm north of Utqiagvik. The low that was over St
Matthew Island will move over the Seward Peninsula at 516 dam
with the trough extending south over Dillingham and the Pacific.
Ridging that was over the Western Bering Sea will rotate east of
the Dateline over the Central Bering Sea. Saturday afternoon the
low that was over the Seward Peninsula will fill as the trough
moves east to lie from Deadhorse to Fairbanks to Whittier. Ridging
over the Bering Sea will move over the West Coast and Chukchi Sea.
Sunday morning the trough will exit to the east while the ridging
will continue to rotate over the state with the axis over Bristol
Bay to Wainwright with strong southwest flow developing over the
Bering Sea. At 850 hpa...-10C isotherm lies from Chicken to
Shishmaref this afternoon while the -20C isotherm has been pushed
north of the Arctic Coast. By Saturday afternoon the -10C isotherm
will be pushed to the south slopes of the Brooks Range while the
0C isotherm will make an appearance over the Northeast Bering Sea.
Sunday afternoon the -10C isotherm will lie from Dawson YT to
Deadhorse then northwest, while the 0C isotherm will push north
over the St Lawrence Island, the Lower Yukon Delta, Norton Sound,
and the southern half of the Seward Peninsula. The warmer
temperatures will moderate rapidly Sunday evening as them move
inland with only some remnants of the warmer air making it into
the Western Interior.

Surface...High pressure extends west over the Arctic from a 1027
mb high just north of Banks Island. Low pressure is holding over
mainland Alaska with a 1016 mb low in the White Mountains moving
east, while a 990 mb low has moved to the Bering Strait and a 981
mb low is near St Matthew Island this afternoon. High pressure
is holding over Southcentral and the Gulf of Alaska. Not a lot of
change by Saturday morning as the lows to the west move over the
coast with a 1002 mb low in Kotzebue Sound, and a 1003 mb low near
Hooper Bay. High pressure will be pushing northwest into the
Upper Tanana Valley and west over the south slopes of the Brooks
Range with weak low pressure in the Upper Yukon Flats. High
pressure will push northwest into the Central Interior Saturday
and the lows to the west will decay and move northeast merging
into the low pressure in the Arctic Plain. A strong low that is
near Kamchatka will move into the Western Bering Sea with a front
extending east along 50N. The low will move northeast into the
north central Bering Sea and the front will move to the Lower Yukon
Delta Saturday night and into the Western Interior by Sunday
morning as the low moves into Chukotka. The front will push into
the Central and Eastern Interior late Sunday.

Arctic Coast and Brooks Range...Relative quiet continues. Stratus
and flurries, but otherwise quiet weather. Some patchy fog. Winds
along the coast mainly east 5 to 15 mph. Inland winds in the
plains winds variable to 10 mph, while in the Brooks Range winds
south at 5 to 15 mph. Low overnight zero to 20 below, while highs
Saturday will range from 10 above to single digits below for most
areas.

West Coast and Western Interior...The beat goes on, snow will
taper off for a few hours, then the next system moves in with more
snow. Another round of heavy snow starting late Saturday night may
be punctuated by some freezing rain as a strong push of warm air
will push temperatures into the 30s above Sunday. Heavy snow
expect in the Kotzebue Sound Region, and in the Kobuk and Noatak
basins. Heavy snow will move into the Western Interior Monday
morning. See latest Winter Storm Watches for details. Winds
generally northeast to east at 5 to 20 mph. Lows overnight range
from around 5 above on St Lawrence Island to the single digits
above and below in the inland areas. Highs Saturday range from
20s above on St Lawrence Island and in coastal areas south of the
Bering Strait to the teens inland and north of the Bering Strait.

Central and Eastern Interior...Light snow tapering off this
evening, then another round of snow Saturday during the day.
Potential heavy snow Sunday night and Monday, see Winter Storm
Watches for details. Snowfall trough Saturday night 1 to 3 inches.
Winds variable to 10 mph, except increasing to south 15 to 25 mph
and gusty near the Alaska Range passes Saturday. Lows overnight
in the single digits above and below. Highs Saturday will range
from around zero in the Upper Yukon Flats to the teens above.

Coastal Hazard Potential Days 3 and 4...Elevated water levels
expected in the Norton Sound Region Sunday night and Monday.
Similar to system that brought elevated water to the area a
couple weeks ago. Will continue to monitor the situation.

Extended forecast for days 4 to 7...Snow will be ending Tuesday
with clearing behind it for Wednesday. Another moisture laden
system will move to the West Coast on Wednesday evening, then into
the Interior with another round of potentially heavy snow that
will last into Saturday before tapering off. We will get a shot of
colder temperatures on Wednesday between systems with temperatures
falling into the 20 below to 35 below range before warming rapidly
back up. Snowfall Thursday through Saturday looks to be a
significant amount, so we will be tracking the systems progress
through the weekend as it may impact travel over the Christmas
holiday.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...

Winter Storm Watch for AKZ208-AKZ209-AKZ213-AKZ216-AKZ217-AKZ219-
AKZ221-AKZ222-AKZ223-AKZ225-AKZ226.

Winter Weather Advisory for AKZ212-AKZ214-AKZ215-AKZ216-AKZ221.

Brisk Wind Advisory for PKZ200-PKZ210-PKZ215-PKZ220-PKZ230-
PKZ235-PKZ240-PKZ245.

&&

SDB DEC 21