Winter Storm and Heavy Snow in Alaska, March 4 to 6, 2022

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
550 AM AKST Fri Mar 4 2022

.ANALYSIS AND UPPER LEVELS...Friday's weather pattern is being
dominated by a deep upper low over the eastern Bering with strong
ageostrophic flow over interior Alaska. An enhanced pressure
gradient at the surface, stretching from the low to across
Southwest into Southcentral, is promoting elevated southeasterly
winds ranging from 20 to 35 mph from Bethel into the Alaska
Peninsula. Gale to storm force southwesterly winds are persisting
over the eastern Bering this morning but should shift northward by
midday. A winter weather advisory is also in effect for the
Kuskokwim Delta where light snow amounts combined with elevated
winds may promote blowing snow and reduced visibility through the
morning and afternoon hours.

Further east into Southcentral a trough is making its way into
the Gulf with strong warm air advection offshore of the coast.
Rain has been observed across Kodiak and as far east as Cordova.
While temperatures across the Copper River Basin and Mat-Su are
largely below freezing, the Anchorage Bowl into the Kenai borough
will remain above freezing into the start of the weekend. The bulk
of precipitation across Southcentral will be confined to
southeasterly upslope flow over the mountains along the coast on
Friday.

&&

.MODEL DISCUSSION...
The next storm system is forecast to bring snow into Southcentral
on Saturday. Models are exhibiting some discrepancies as far as
the the speed of the low is concerned, which will effect the
duration of snow across Southcentral and how quickly it comes to
an end for Anchorage in particular. On the one hand, models have
all trended the ridge axis further east, keeping Southcentral
temperatures cooler. This should allow for all snow across the
Anchorage Bowl and alleviate any ptype concerns. On the other
hand, models have not lined up in agreement with timing of the
low. The NAM and GEM Regional are currently the fastest solutions
with snow beginning later on Saturday and coming to an end across
Anchorage early Sunday morning. The EC is the middle ground
solution with snow coming to an end by mid-morning on Sunday.
Lastly, the GFS is even slower with snow coming to an end by late
morning or closer to midday on Sunday. While confidence has
increased that Southcentral will experience snow over the weekend,
low confidence is noted in respect to timing and total amounts.
Should the NAM or GEM Regional verify then lower snow
accumulations can be expected with slightly higher amounts
possible should the GFS and EC be closer to the truth.

&&

.AVIATION...
PANC...Winds across Anchorage have begun to transition to a
southeasterly direction this morning in response to a deep upper
low over the Bering. As low pressure lifts further and further
north of the PANC latitude Turnagain Arm winds will start bending
more so into our area. While winds offshore and over the Turnagain
Arm could gust to as high as 60 knots, winds over PANC should be
somewhat milder with peak gusts to around 35 knots from late
morning through around noon. Winds will gradually diminish later
this afternoon and evening as low pressure departs the region.
Otherwise, expect VFR conditions to prevail into Saturday.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Sunday night)...

A strong frontal system over the western Gulf early this morning
will track across the northern and central Gulf today, with a
barrier jet setting up along the north Gulf coast. Precipitation
will initially be light across the eastern Kenai Peninsula and
Prince William Sound areas. However, precipitation will become
heavier tonight into Saturday as a strong southerly jet sets up,
transporting deep moisture from the Pacific. Low level upslope
flow will also enhance precipitation in the coastal zone.
Temperatures are above freezing across the communities of Prince
William Sound. With some colder air aloft, there may be snow at
times, but expect mostly rain at and near sea level, with rising
snow levels tonight into Saturday.

Meanwhile, inland areas of Southcentral will remain mostly dry
today, with the exception being some light snow over the northern
to western Susitna Valley. The big story will be widespread gusty
winds as a deep low tracks northward along the west coast of
Alaska. In particular, Anchorage and the Matanuska Valley will see
some strong and gusty winds along with balmy temperatures in the
lower to mid 40s. Winds will quickly die down this evening,
allowing temperatures to cool back down to freezing or below
overnight tonight.

This will set the stage for a widespread snow event Saturday-
Saturday night. A weak low will track up a cold front from the
Pacific to the western Gulf. Solutions have all shifted eastward
with the track of this low over the past 24 hours, now bringing it
east of Kodiak Island, south of Seward and ultimately into Prince
William Sound. This new track means that all areas north and west
of the low track will remain all snow, including the western Kenai
Peninsula, Anchorage, and the Matanuska Valley. This was very
much in question with the further west track from 24 hours ago.
However, there is still forecast uncertainty in precipitation
timing and snow totals, as model solutions vary on the speed of
the upper level trough coming in from the Bering Sea as well as
the speed of the surface low into Prince William Sound. Have
decided to lean toward the faster solution with this forecast
package, but confidence in the end time of snow is low.

So, expect snow to overspread most of Southcentral Saturday
morning (with rain and snow along the coast as mentioned earlier).
Precipitation will then end from west to east Saturday night
through Sunday. The speed of the key features will determine the
duration and amount of precipitation. Based on the
orientation/approach of the upper level short-wave, it looks like
the heaviest precipitation will be from eastern Prince William
Sound to the Copper River Basin, especially along the south slopes
of the mountains with strong south-southwest upslope flow.
Secondarily, cold air advection on the back side along with a
secondary short-wave will favor the west side of the Chugach
Mountains from Anchorage to the Mat Valley. Stay tuned, as we
will continue to fine-tune snow amounts across the region as we
get a better idea of the timing of track/timing of the upper
trough and surface low.

With a high amplitude ridge building behind the exiting trough
Saturday night, expect cold air advection to push offshore and
result in strong gusty gap winds along the coast. This should also
help clear out at least some of the low level moisture. As a
result, expect abundant sunshine to develop across the region
during the day Sunday. As the active weather pattern continues,
another low will make its way north from the Pacific Sunday night,
likely bringing another round of rain and wind to Kodiak Island
and the southern to western Gulf of Alaska.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 to 2 - Today through
Saturday night)...

A relatively small but potent low pressure is now moving onshore
along the Kuskokwim Bay with a relative calm passing into southern
portions of the Kuskokwim Delta near the center. Gusty easterly
winds, falling snow and blowing snow will continue north of
Toksook Bay until the low passes overhead later this morning,
leading to briefly improved visibility before stronger southwest
winds gusting as high as 55 mph kick in before noon as the low
advances farther north into Norton Sound. A Winter Weather
Advisory remains in effect for the Kuskokwim Delta Coast where
periods of blowing snow will continue to significantly reduce
visibility at times. Conditions should rapidly improve later this
afternoon and evening as the low departs, with snow ending from
south to north and southwest winds dying off by this evening.
Gusty southerly winds over the Middle Kuskokwim Valley and Bristol
Bay will similarly diminish by this afternoon as the low exits,
with temperatures in the mid 30s to low 40s warm enough for a mix
of rain and snow with passing showers before all precipitation
clears out this afternoon.

By tonight, a shortwave trough will approach from the eastern
Bering Sea, with an embedded small wave expected to pass over the
Kuskokwim Mountains and northern Bristol Bay. A few snow showers
will move through with the trough passage, mainly across the
Kuskokwim Delta tonight and later over parts of interior Bristol
Bay for Saturday as the main trough shifts east. Any snowfall with
this system is expected to be light, with little to no
accumulation. A high pressure ridge will move into place by
Saturday night, ushering in calm winds, cooling temperatures
dropping into the 10s and 20s and clearing skies.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 2 -
Today through Friday night)...

A small low pressure trough will move across the eastern Aleutians
today, sending a quick round of rain and snow showers and winds
up to small craft along the eastern Aleutians and southern Alaska
Peninsula through this afternoon. Elsewhere, convective snow
showers feeding off of slight marine layer instability will
occasionally impact the rest of the Aleutian Chain and Pribilofs
through this afternoon. By this evening, a strong North Pacific
low will send a front into the western Aleutians, bringing in a
mix of rain and snow along with strong east to southeast winds
increasing up to storm force between Kiska Island and Adak by
Saturday morning. The parent low will move north over Attu by
Saturday afternoon as the then occluded and weakening front
advances a narrow band of rain and snow into the central Aleutians.
Winds along the western Aleutians will shift to westerly as the
low moves north into the Bering by Saturday night, while the
aforementioned front stalls out and begins to fall apart west of
the Pribilofs.

&&

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

Gulf of Alaska: A Northern Gulf low moves along the front to exit
the Southeast Gulf for Tuesday. Forecast confidence is good.
Gusty Southerly winds accompany the front into the Eastern Gulf.
High end Westerly gales extends from Kamishak Bay through the
Barren Islands into the Gulf, diminishing Monday, but returns on
Tuesday. Gusty winds South of Kodiak Island to the Alaska
Peninsula Coast through Tuesday. Seas building to 18 feet from the
Alaska Peninsula Coast through Tuesday.

Bering Sea: A strong Western Bering low moves into the Chukchi
Sea by Tuesday. Its front extends through the Central Bering and
Aleutians through Tuesday. Forecast confidence is good. This wind
wrapped low and front brings high end gales, diminishing Monday.
Seas to 22 feet, subsiding. A new well developed low and front
approaches the Western Aleutians and Bering for Tuesday. Gusty
winds increase to Southerly high end gales with areas of storm
force winds spreading into the Central Aleutians and Bering,
diminishing late Monday. Seas building to 28 feet over the
Aleutians and Bering, subsiding Tuesday.

&&

.Long Term Discussion (Days 4 through 7: Monday through
Thursday)...

At the onset of the forecast period, the longwave pattern will be
amplified. Monday expect a ridge over the east Pacific and a
ridge over the Eastern Bering with troughs over mainland Alaska
and over the western Aleutians. As the forecast period unfolds,
the east Pacific ridge will get shunted but the ridge that was
over the Eastern Bering will move over Mainland Alaska. All the
while there will be a broad area of troughing over the Pacific
Northwest, Western Bering and Kamchatka. The models show negative
height anomalies at 500 mb over the Western Bering and NW Pacific
for much of the period. Whereas, the models have positive height
anomalies over the Chukchi Sea, Mainland and the Gulf Of Alaska
through March 11th. A series of lows will rotate through the base
of the western Aleutians trough likely keeping conditions
generally unsettled into next week from the Aleutians to the
Alaska Peninsula. Above average temperatures should prevail across
much of Mainland Alaska through next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 155.
MARINE...Storm: 130 175 177 180.
Gale: 119 120 131 139 141 160 165 173 174 176 178 411-414 351
      352.
. FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
MARINE/LONG TERM...MK/PJS