Blizzard and Winter Weather in Alaska, February 13 to 14, 2022

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
445 PM AKST Sat Feb 12 2022

.ANALYSIS AND UPPER LEVELS...

An upper-level shortwave and associated surface trough over Prince
William Sound continue to produce light snow in an area from the
Mat-Su Valleys east along the Southcentral Coast and over higher
elevations. Light snow is tapering off to scattered snow showers
along the Kenai Peninsula and northern Gulf, as these features
continue to lift northward. A few breaks in the cloud cover, along
with some sunshine, are also of note across Cook Inlet south to
Kodiak Island.

A second upper-level wave and associated surface low sit over
coastal Southwest Alaska this afternoon. These features are also
producing areas of light snow across this region along with some
gusty winds along the coast, closest to the center of circulation.

Farther west, a weak and transient ridge is parked over the
central Aleutians, providing for a rather quiet day weatherwise,
with the exception of a passing shower, from Unalaska to Adak. A
vertically stacked low near Shemya is keeping clouds and showers
over the western Aleutians along with northeasterly gales over the
western Bering.

&&

.MODEL DISCUSSION...

Model agreement remains fairly decent ironing out the bigger
picture of a continued active pattern with good run to run
consistency through the short term. Given this, the current
forecast looks on track; however, subtle differences in the
position and timing of the various shortwaves embedded in the
upper-level flow persist. The first difference is that the NAM
continues to advertise a slight stronger wave moving over
Southwest Alaska for Monday while the GFS/EC/GEM weaken this
feature quickly as it pushes inland. While the outlier currently,
if the NAM does pan out, it would mean a longer duration of light
snow across Southwest for Monday prior to the next system arriving
late Monday into Tuesday. As for this next system, the NAM and
GEM continue to keep the stronger series of shortwaves a bit
farther south than the GFS and EC. The NAM is also the stronger of
the solutions, trying to strengthen each wave into their own
compact upper-level low. The farther north solutions would also
result in the stronger advection of warm air aloft over Southwest
Alaska and the western half of Southcentral Alaska, raising
precipitation type concerns, perhaps as far north as Anchorage and
Palmer. The NAM and GEM would still introduce a wintry mix over
Southwest, but keep slightly colder air place over Southcentral,
with a snowier solution. The GEM is the fastest solution, moving
the bulk of this system out of the area Tuesday morning, a good 12
hours earlier than other models.

&&

.AVIATION...

PANC...Prevailing MVFR conditions with lower ceilings and reduced
visibility due to occasional light snow are expected to persist
through late Sunday night. Brief IFR conditions are possible by
Sunday morning as widespread light snow redevelops over the
terminal. The snow is expected to come to an end by early Sunday
afternoon. Southerly winds will remain light through Sunday.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through
3...Tonight through Tue afternoon)...

An upper level shortwave trough continues to lift northward
through Southcentral through this evening. As a result, expect
flurries to continue throughout the Anchorage Bowl to Matanuska
Valley at least until the early evening hours when the axis of the
upper trough passes through. This will also result in a reduction
of the snowfall rates in and around Hatcher Pass this evening
with continued light snow through the overnight hours. Another
upper level shortwave in the overall flow is expected to lift
northward overnight that will work in tandem with another upper
level trough pushing eastward from Southwest Alaska. The two of
these will work together bringing more moisture northward as well
as add more lift into the atmosphere heading through the day
Sunday. Therefore, expect snowfall rates to increase for Hatcher
Pass where another 6 to 8 inches of snow may accumulate leading to
a storm total there of 12 to 18 inches. The big update this
forecast package was to bring likely snow into the Anchorage Bowl
for Sunday with up to a 0.5" for the west side of town with up to
1 inch on the Anchorage Hillside. This will also bring another
round of snow to the Mat-Su Valleys with 1 to 5 inches expected.
Highest amounts will be across the northern Susitna Valley (north
of Talkeetna).

Passage of the upper level trough is expected Sunday evening/night
which will largely end precipitation for all areas as drier air
and heights build over the area. With the westerly flow aloft,
current thinking is that any clouds in the area will be pushed up
against the Chugach Mountains which may help to keep the clouds
in place Sunday night into Monday morning without fully clearing
out. This of course is playing with the temperature forecast as
less clouds will cause temperatures to fall more whereas if it was
cloudier temperatures won't fall as much.

Lastly, another system is expected to move northward towards
Southcentral from south of Kodiak Island on Monday. For Kodiak
Island, current thinking is precipitation may start as snow with
little to no accumulation before changing over to rain as milder
air works in. As the system continues northward, another
widespread snowfall event favoring Hatcher Pass in terms of the
avalanche areas is expected for Monday night through Tuesday. Much
uncertainty continues to exist in terms of timing as well as
amounts and just how much warm air will come in with this system.
This will continue to be fine tuned over the next couple of days.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3 - Tonight
through Tuesday)...

Light snow showers continue across Southwest Alaska tonight as a
weak surface low in the eastern Bering tracks slowly toward the
coast. The Kuskokwim Delta should see their last snowflakes from
this system around midnight as drier air sweeping across the
Southwest begins to shut off the snow showers from west to east.
By Sunday afternoon, only the western slopes of the Alaska Range
will be seeing light accumulation. In the wake of the low, dry air
and a transient will ridge will allow some portions of Southwest
to see briefly clearing skies before the next storm system moves
in. Monday morning, an occluded front reaches the Southwest coast
and provides a brief round of snow for Bristol Bay and the
potential for blowing snow to the Kuskokwim Delta. The snow turns
showery in the afternoon, with the front weakening as it moves
inland.

However, a second front with stronger upper-level support is
expected to push ashore Monday evening and reinvigorate
precipitation. A stronger push of warm air aloft is expected with
this front, leading to an uncertain precipitation type forecast
for Monday night. Precipitation is expected to start as snow, but
with low-level easterly flow expected ahead of the front, it will
be possible for cooler temperatures to hang on near the surface
while warmer air works in aloft, allowing for a brief change to a
wintry mix with some potential for freezing rain in Bristol Bay.
The main question with this will be timing, though, as
precipitation is expected to begin tapering off around the time
this change is expected to occur. The most likely locations for
any ice accumulation is currently expected to be the northern
coast of Bristol Bay from the western capes to west of King Salmon
and north into the inland valleys. Warmer air is expected to work
its way in near the surface farther east more quickly, which
should lead to a primarily rain event with the second front for
King Salmon. Winds then turn southerly overnight and warm air will
move in near the surface leading to some light rain showers
behind the front on Tuesday morning.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3 - Tonight
through Tuesday)...

A large storm system will approach the Aleutians Sunday morning.
Its strong front will push north across the Aleutian Chain
through Sunday, bringing storm force winds with winds gusting to
near hurricane force to the central and western Aleutians. A
Winter Weather Advisory has been issued for the Pribilof Islands
as the front brings blowing snow to the islands Sunday evening
through Monday morning. As the front progresses northward across
the Bering snow will abate, allowing for improved visibility. Storm
force winds continue across the western Bering Sea through Monday
night as the front sweeps northward. This storm will continue to
move northwestward and winds are expected to gradually ease on
Tuesday. This storm will also produce large long period 20ft+
swell across the western and central Bering Sea Sunday morning
through Monday night.

&&

.Marine (Days 3 through 5: Tuesday through Thursday)...

Gulf of Alaska:

A front extends across the Northern Gulf with a couple of low
centers moving along the front through Thursday. Forecast
confidence is fair with movement of the lows. Gusty Westerly winds
move across the Southern Gulf by Wednesday. Seas to 16 feet,
subsiding. A new front enters the Western Gulf Wednesday,
spreading across the Gulf through Thursday. Gusty Southwest winds
with areas of gales move along the front through Thursday. Seas to
14 feet, subsiding Thursday.

Bering Sea/Aleutians:

A well developed North Pacific low moves across the Western
Aleutians Tuesday and back into the North Pacific for Wednesday.
Forecast confidence uncertain with the tracks and developments of
the lows. Widespread high end Northeasterly gales with areas of
storm force winds extends over the Bering and move to the West
with the low. Seas to 25 feet over the Western Bering, subsiding
Thursday. Seas to 20 feet on the Pacific side of the Aleutians,
subsiding Wednesday. A second well developed North Pacific low
approaches Western and Central Aleutians for Thursday. Southerly
gales on the Pacific side of the Pacific side of the Aleutians.
Seas building to 20 feet ahead of the low, subsiding Thursday.

&&

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

The long term begins Wednesday with the all too familiar longwave
trough/ridge pattern holding across the region. The longwave
trough remains cemented in place from the Beaufort Sea southwest
to the western Aleutians, anchored by a pair of deep upper-level
lows south and west of Attu. Downstream, the upper- level ridge
extends from the eastern Pacific north into the Gulf of Alaska.
Between the two, a progressive pattern of embedded shortwaves
moves from the north Pacific toward Southwest Alaska, following
the southwesterly flow aloft. The stagnant longwave pattern look
to remain in place through Friday, before the deep upper- level
low south of Attu begins to push east and the entire trough axis
centers over the state late Friday into early Saturday. The
movement of this low, however, looks to only shift the longwave
trough temporarily, as this low is quickly replaced by another
moving up from the western Pacific. This second upper- level low
reestablishes the blocky longwave pattern as the upper-level ridge
that exited the Gulf of Alaska at the end of the week returns by
the weekend along with embedded shortwaves in the southwesterly
flow between the two.

At the surface, this is reflected in an active pattern with
multiple storms systems moving from the north Pacific south of the
Aleutian Chain northeast toward Southwest and, ultimately,
Southcentral Alaska. The first of these systems lifts north across
the eastern Aleutians and the Alaska Peninsula, with a surface low
near Cape Newenham, by Wednesday morning. Models differ on
exactly how far north this low and its associated front will
travel before a triple point low forms along the front in the
western Gulf. The EC and GEM spin up the low by Wednesday
afternoon, while the GFS is delayed, allowing warmer air with this
system to push farther inland. The differences stem from the
interaction of two upper- level shortwaves. The EC and GEM both
strengthen the southernmost of the two and phase the energy from
the northern one into it. This is what allows the triple-point low
to spin up faster and allow for a faster eastern progression, as
this system exits the region Thursday morning. The GFS keeps both
waves separate, with a stronger northerly wave. With the bet
dynamics to the north, the GFS pushes the low and front into the
interior of the state, delays the development of the surface low
in the Gulf and slows the progression of the system across
Southcentral until Friday morning. With a more northerly track and
robust intrusion of warmer air, the GFS solution would also
introduce precipitation type concerns for the interior of the
Southern Mainland.

With the overall pattern remaining progressive, the next system
moves in quickly on on the heels of the first, moving across the
Aleutian Chain and over Southwest Alaska by Friday morning. This
system moves over Southcentral by Saturday and exits the region
late Saturday as the next system moves from the eastern Aleutians
to Southwest Alaska by late Saturday and across the Southern
Mainland for Sunday. Precipitation type will be a concern with
each system, especially across the Alaska Peninsula, Bristol Bay,
and Southcentral coast.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 195.
MARINE...Storms: 176, 177, 178, 411.
         Gales: 155, 170, 172, 173, 174, 175, 179, 185, 412, 413, 414.
         Heavy Freezing Spray: 179, 185, 411, 412, 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...MV
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
MARINE/LONG TERM...MK/TM