Winter Storm in Alaska, November 25 to 27, 2021

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
521 AM AKST Thu Nov 25 2021

.ANALYSIS AND UPPER LEVELS...

Teleconnections continue to support a deep upper level trough
continuing to extend across the Alaskan mainland which will allow
for the unseasonably cold temperatures to continue across the
region. An upper low inside of this upper trough is currently over
southern Cook Inlet and is moving northeastward. Upper level
ridging extends across the western Bering/Aleutians. The
jetstream remains south of 50N west of 140W and then extends
northeastward to over the Alaskan Panhandle.

Closer to the surface, radar imagery shows convective snowbands
moving northwestward from the northern Gulf into Prince William
Sound. Radar also shows light stratiform snow over Cook Inlet and
the western Kenai Peninsula.

&&

.MODEL DISCUSSION...

Guidance generally remains in good agreement with respect to the
placement and intensity of synoptic scale features at both the
surface and in the upper levels. The biggest area of forecast
uncertainty are these mesoscale snowbands across Prince William
Sound as guidance struggles to resolve these smaller scale
features. Overall forecast confidence remains above average,
though there is lower confidence with respect to exact snow
amounts in Prince William Sound.

&&

.AVIATION...
PANC...MVFR conditions are primarily expected before 26th/03z as
visibility will remain between 6SM and 3SM. Ceilings will begin
around 5000ft with temporary 3000ft ceilings before 25th/15z.
Ceilings will then fall to 3000ft from 25th/15z to 25th/20z before
rising to 4500ft.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 to 3)...

An upper level low is currently over southwest Alaska while a
surface low is located near Seward. Cold air advection from the
Alaska mainland continues to force dense arctic air through the
gaps and passes of the Alaska Range, resulting in gusty
northwesterly winds, scattered snow showers, and areas of blowing
snow across southern Cook Inlet. The Barren Islands, Shelikof
Strait, and Kamishak Bay will continue to see the strongest winds,
and the area west of the Barren Islands can expect storm-force
winds with possible hurricane-force gusts. Thus, heavy freezing is
also a concern for these areas and stretching up into Cook Inlet.
These conditions are expected to persist through Thursday. The
cold air advection from the Mainland and the warmer temperatures
over the Gulf have set up a tight temperature gradient that runs
along the Alaska Range. The resulting westerly offshore flow will
be responsible for creating blizzard conditions for Whittier
through this morning. Expect gusts as high as 45 mph, reduced
visibility to one quarter of a mile or less due to blowing snow,
and additional snow accumulation up to 6 inches. Please see our
Blizzard Warning for more information. The upper level low slowly
waddles toward Prince William Sound early Friday morning and then
Inland by Saturday. Increased instability will result in periods
of locally heavy snow showers across the eastern Sound, especially
for Cordova and Thompson Pass, late Friday and early Saturday.

The surface low spinning near Seward continues to be plagued by
model uncertainty regarding its exact timing and track. This
creates a challenging PoP and snow amount forecast because the
exact orientation of the system is hard to nail down. Thus, we have
kept PoPs fairly broad brushed over inland areas such as
Anchorage. Limited snow accumulation of 1-2" is possible for the
Anchorage Bowl. Another area of concern includes the western Kenai
Peninsula. With cold air blasting across the open waters of Cook
Inlet, there remains potential for snow bands to set up and bring
snow to parts of the Sterling Highway. Holiday travelers should
check their local forecast as we will update this throughout the
day.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Sat night)...

Quiet and dry weather conditions are expected to continue for much
of Southwest for the next couple of days. The only exceptions will
be along the Kuskokwim Delta Coastline and along the Alaska
Peninsula where snow showers are expected to continue. Arctic air
continues to pour southward through the Bering Strait to the
northern Bering Sea picking up moisture as it does so. As a
result, light snow showers are expected to continue for places
such as Hooper Bay and Chevak south to Toksook Bay for the next
couple of days as the flow remains northwesterly. This will aid in
pushing some moisture onshore in this area. Any snow accumulation
will be very light/minor. Snow showers will continue along the
Alaska Peninsula (Cold Bay, Nelson Lagoon, and Port Heiden) through
tonight as Arctic air continues to pick up moisture as it moves
southward across the Bering. What kind of weather does a turkey
like? "Fowl Weather!" Since the Alaska Peninsula will endure snow
showers throughout the day. Gusty winds will also accompany the
snow shower activity leading to visibilities being reduced to as
low as one half mile at times. See the Special Weather Statement
for more details. Elsewhere across Southwest, expect frigid
conditions to continue as Arctic air continues to be pulled
southward on the backside of an upper level low over the Barren
Islands area.

Temperatures are expected to be mostly in the single digits below
zero for interior areas with single digits to near zero along the
coastal areas for Thanksgiving Day. Highs are expected to be
colder across the Lower Kuskokwim Valley on Friday with highs in
the teens and single numbers below zero. Elsewhere, expect mostly
single digits to near zero. Overnight lows tonight and Friday
night are expected to be very cold once again dependent on cloud
cover but where it is clear and calm; expect temperatures in the
teens to 20s below zero. More widespread 20s below zero are
expected Friday night due to clearer and more calm conditions.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Tonight through Sat night)...

Arctic air continues to spill southward across much of the Bering
Sea for Thanksgiving Day which will continue through Sat night.
As a result, expect snow showers to continue for the Pribilofs and
Eastern Aleutians (Dutch Harbor) through this evening. Snow
showers combined with at times gusty winds upwards of 20 to 30 mph
may reduce visibilities to as low as one half mile. As we move
through the evening hours, expect any snow shower activity to
become more isolated with the threat for snow showers continuing
through Sat night; just not as widespread or frequent.

Next, a system moving across the North Pacific today will spread
small craft advisory winds mostly to the marine waters south of
the Chain. Expect some on and off snow showers for Shemya and the
Adak area as this low moves off to the east.

Lastly, some upper level energy is expected to be left behind from
the previous system which will phase with another systems energy
moving northward. This system is expected to intensify into a gale
force low pressure system Friday night. The low isn't expected to
move all that much and there remains uncertainty as to exactly
how far north or south the front associated with the system will
go. However, expect gale force winds with potentially storm force
gusts to remain fairly stationary over the same areas from Friday
night through Saturday night. Also, expect warmer temperatures
aloft and at the surface to change any snow or rain/snow mix
Friday night to rain during the day Saturday for places such as
Adak and Shemya.

&&

.MARINE (Days 3 through 5: Friday through Sunday)...

Gulf of Alaska...Cold Arctic air through gaps along the Gulf
coast may produce high end small craft to gale force winds
through Monday. The Gulf will likely be impacted by a deep low
moving out of the northeast Pacific on Monday. While the track
is uncertain, Gales are likely across much of the Gulf waters
with the possibility of Storm force winds along the leading
front.

Aleutians/Bering Sea...High pressure ridge exists over the
eastern Bering Saturday through Sunday morning. A front off a
North Pacific low enters the western Bering on Saturday and
pushes eastward, encompassing a majority of the Bering by Sunday
afternoon. Seas 15-20 ft are likely along the Central/Western
Aleutian coastal waters Saturday and Sunday, with winds near
Gale force (Central Aleutians) and at or above Gale force
(Western Aleutians). Winds and waves begin to diminish by
Monday as the low moves toward the Gulf of Alaska.

&&

.Long Term Discussion (Days 4 through 7: Saturday through
Wednesday)...

The cold pattern continues as the Arctic airmass holds strong.
Expect temperatures to remain frigid, reaching into the -20’s
for inland areas across Southern Alaska. A digging trough will
help force these winds through gaps in the Western Alaska Range
and Kamishak Bay, producing increased wind and the potential for
heavy freezing spray. High amplitude ridging persists over the
eastern Bering on Sunday, until the front off an incoming North
Pacific low forces it onshore over Southwest Alaska. The low
tracks south of the Aleutian Islands in its journey towards the
Gulf of Alaska. The front moves along the Chain, producing gusty
winds and falling precipitation to the area Sunday and Monday.
With another surge of Arctic air on the back side of this the
potential for snow and blowing snow is high.

The front enters the Gulf by Monday, bringing rain and snow to
the Gulf and coastal regions. The parent system looks to develop
a secondary system in the base of its trough late Monday
night/early Tuesday morning, and merge. The new system moves along
the Southeast Coast through Tuesday before reaching the North
Gulf Coast Tuesday night. There is uncertainty in the exact tracks
of these lows across the Gulf. However, the pattern looks
favorable for periods of heavy snow along the coastal mountains
beginning Monday and continuing through at least mid week. There
might be enough warm air at sea level to cause snow to mix with or
change to rain.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 125.
MARINE...Heavy Freezing Spray Warning 121 130 137 138 139 140 150 160 165
180 181.
Storm Warning 130.
Gale Warning 120 131 132 138 150 155 351 352.
FIRE WEATHER...NONE.
&&

SYNOPSIS AND MODEL DISCUSSION...ED
SOUTHCENTRAL ALASKA...AF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
MARINE/LONG TERM...KM

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
345 AM AKST Thu Nov 25 2021

AKZ181-185-195-260600-
Alaska Peninsula-Eastern Aleutians-Pribilof Islands-
Including the cities of Cold Bay, Sand Point, Unalaska, Nikolski,
and Saint Paul
345 AM AKST Thu Nov 25 2021

...OCCASIONALLY HEAVY SNOW SHOWERS AND STRONG GUSTY WINDS EXPECTED
TO CONTINUE THROUGH THIS EVENING ACROSS THE EASTERN BERING...

Snow showers and gusty northwesterly winds are expected to
continue across the Alaska Peninsula, Pribilofs, and Eastern
Aleutians through this evening. Arctic air continues to move off
the Alaska mainland and over the relatively warm water of the
Bering. Thus, the atmosphere will continue to be moistened and
contribute to snow shower development through this evening as the
pattern remains stagnant.

Wind gusts ranging from 30 to 40 mph this morning will slowly
subside to 20 to 30 mph by this evening. As a result, any falling
snow combined with the gusty winds could reduce visibility to as
low as one half mile at times. Locations that continue to be
impacted by these adverse conditions include False Pass, Port
Heiden, Cold Bay, Dutch Harbor, and Saint Paul.

Widespread snow shower activity throughout the morning and into
the afternoon will become more isolated in nature during the
evening.