Winter Storm in Alaska, September 9 to 12, 2020

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
114 PM AKDT Wed Sep 9 2020

.SYNOPSIS...
A wet southwest flow pattern over Northern Alaska will turn
westerly tonight as a cold front along the West Coast makes its
way east to the Alcan Border by Thu morning. This continues to
cause rain and rain showers over most of Northern Alaska, with
snow above 4000-500 feet. Rain will taper off from the west behind
the cold front this evening and tonight, with snow levels falling
to 2000-3000 feet in most areas by late tonight. Over the North
Slope the freezing level is near the surface north and west of
Umiat and 3000-4000 ft in the Brooks Range, but will fall to the
surface to 2000 ft over the Brooks Range tonight and remain there
through Fri.

Expect an additional 0.15-0.25 inch of rain over most areas south
of the Brooks Range through tonight. Expect 1 to 2 inches of snow
in the Brooks Range above 3000 ft through Thu, and less than 1
inch below 3000 ft. Heavier snow of 6 to 10 inches is possible in
the Ern Brooks Range from Thu night through Sat where a Winter
Storm Watch Remains in effect.

Westerly winds of 20-30 mph are expected to spread across the
Arctic Coast tonight and Thu, with winds increasing to 25 mph
gusting 30-40 mph Thu night and Fri. This is expected to cause
elevated surf along the Arctic Coast Thu into Fri.

Remnants of Super Typhoon Haishen will move into the Bering Sea
Fri and Sat and cause a very deep low to develop over the
southwestern Bering Sea Fri and Sat. This will mainly cause east
winds over the West Coast of Alaska this weekend.

&&

.DISCUSSION...
Models, the 12z models suite initialized well against the 12z
surface analysis and verified well against the 18z surface
analysis as far as feature location, however the low over Western
Alaska initialized a couple of mb too high as did the low to the
north of Wrangel Island. Model spread was reasonable in the short
range as well as the mid range, however significant differences
emerge on track and strength of the Western Bering Sea Low by the
end of the week as is often the case when tropical remnants merge
with non tropical low pressure systems. Continuity of this
forecast package was maintained with previous forecast package
with a blend of the GFS and ECMWF.

Aloft at 500 mb, a 542 dam low over the Western Bering Sea will
weaken to 548 dam as a weak ridge over the eastern Bering Sea
slowly pushes onto the West Coast of Alaska through Friday. A
trough over the Eastern Interior will continue to push east into
Canada Thursday and continue east on Friday. The upper level low
in the Western Bering Sea absorbs the remnants of Super Typhoon
Haishen on Friday and will produce a strong low at the surface
over the Western Aleutian Islands Saturday and Sunday. The upper
level low lingers in the Western Bering Sea on Sunday as a front
rotating around the low pushes northeast into an upper level ridge
over Western Alaska and rapidly weakens Sunday and Monday. The
upper level ridge over Western Alaska will produce northwest and
cold flow over the North Slope as well as the Central and Eastern
Alaska into the weekend.

On the surface, a 997 mb low over the western Aleutians meanders
slowly in place and weakens through Friday night before being
absorbed by the fast moving remnants of Super Typhoon Haishen
over the Western Aleutians as a 994 mb low Friday evening. The now
merged low continues to deepen to around 980 mb on Saturday
morning and deepens to 978 mb as the low drifts to the north in
the Western Bering Sea Saturday night and Sunday. A front spinning
around the low continues to stretch and weaken as it approaches
the West Coast of Alaska late on Sunday. Weak high pressure over
the West Coast and Western Interior on Friday will continue to
push east into the Central and Eastern Interior through the
weekend behind an arctic front that will bring a colder airmass to
the Interior and lower snow levels over all of northern Alaska.
Minor snow accumulations are expected above 3000 feet and snow
levels are expected to drop to around 2000 feet as the cold
airmass settles into the Interior.  A 1008 mb low develops along
the tailing end of a trough extending from a low in the Canadian
High Arctic to the north of Point Barrow on Thursday night and
Friday. The low pushes south and east to just north of Demarcation
Point as a 1010 mb low Friday morning and then weakens into a
trough again over the Eastern Brooks Range Friday night and
Saturday. A Winter Storm Watch remain in effect for the Eastern
Brooks Range where 6 to 10 inches of snow is expected with favored
northwest upslope flow beginning Thursday evening and continuing
into Saturday morning.

Coastal Hazard Potential Days 3 and 4...None.

&&

.FIRE WEATHER...
Fire Weather Forecasts have ended for the season. Expect cool and
wet conditions to continue through the week.

.HYDROLOGY...
An additional 0.10 to 0.25 inch of rain is expected through late
tonight in most areas from the Brooks Range south. Between 1 and 3
inches of rain has fallen over the area from the Nulato Hills to
Ambler to Bettles over the past 2 days. This has caused rises on
rivers in the Koyukuk, Kobuk and Upper Noatak Basins which will
continue through the week. Other rivers will see slight rises this
week. At this time no flooding is expected, but the Interior from
the Koyukuk River NW will need to be watch closely this week.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch for AKZ206.

Small Craft Advisory for PKZ215-PKZ230-PKZ235-PKZ240-PKZ245.
&&

CCC SEP 20

Special Weather Statement
National Weather Service Fairbanks AK
529 PM AKDT Wed Sep 9 2020

AKZ201>204-110200-
Western Arctic Coast-Northern Arctic Coast-
Central Beaufort Sea Coast-Eastern Beaufort Sea Coast-
Including Wainwright, Atqasuk, Point Lay, Cape Lisburne,
Utqiagvik, Alaktak, Pitt Point, Nulavik, Nuiqsut, Prudhoe Bay,
Alpine, Deadhorse, Kuparuk, Kaktovik, and Flaxman Island
529 PM AKDT Wed Sep 9 2020

...Elevated Surf Along the Arctic Coast Through Friday...

From Utqiagvik west, west winds 20 to 30 mph are expected to
continue through Friday. This is expected to cause elevated surf
from Utqiagvik west through Friday. The highest surf is expected
Thursday and Thursday night. Minor beach erosion is expected.
People should move belongings inland from the beach to avoid them
being damaged or washed away.

East of Utqiagvik, west winds increasing to 20 to 30 mph on
Thursday are expected to continue through Friday. This is
expected to cause surf to become elevated from east of Utqiagvik
on Thursday with surf remaining elevated through Friday. The
highest surf is expected Thursday afternoon through Friday
afternoon. Minor beach erosion is expected. People should move
belongings inland from the beach to avoid them being damaged or
washed away.