Winter Weather Advisory 69, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
546 AM AKST Mon Dec 13 2021

.ANALYSIS AND UPPER LEVELS...
An occluded upper low is centered over the western Bering this
morning. Its front stretches southeastward over Saint Matthews
Island and down across the Pribilofs. A warm front extends from
the occluded front southeastward and into the Alaska Peninsula
while a cold front trails further west and over the Eastern
Aleutians. Multiple blizzard warnings are in effect, including the
Pribilof Islands, the Kuskokwim Delta and Bristol Bay. Gusty
winds are promoting blowing snow and significantly reduced
visibility. Over the Eastern Aleutians snow has transitioned to
rain across Unalaska with the onset of warm air advection.

As with yesterday cold overnight low temperatures are prevalent
across Southcentral. Morning observations show minus single digit
to minus teen temperatures from the Anchorage Bowl up into the
Mat-Su as cold 850 mb temperatures and calm conditions are
promoting more efficient radiational cooling. Some potentially
good news for some is that the passage of the frontal system into
interior Alaska should begin pushing the arctic air mass eastward
and back into Yukon through the latter half of the week. For
Southcentral in the short term, however, Monday will dawn
cold but clear and calm.

&&

.MODEL DISCUSSION...

Models have been in good overall agreement with the synoptic
picture. Questions regarding the development of a triple point low
later this evening have largely been alleviated with models
zeroing in on its development roughly 155 nm south of Akhiok. Some
discrepancy remains with the intensity of a shortwave trough
moving through Southcentral Monday night. Guidance has trended
weaker though the NAM is the outlier with a more vigorous wave
tracking into Southcentral. Model consensus suggests a short
period of very light snow with negligible accumulations. However,
if the NAM were to verify there could be an extended period of
light snow with at least some accumulation through Tuesday
morning.

&&

.AVIATION...
PANC...VFR conditions will linger throughout the day on Monday
along with light northerly winds. Models bring a shortwave trough
through Southcentral later tonight with a potential round of light
snow. This will likely bring ceilings down to MVFR levels. Due to
questions regarding timing of snow and intensity, overall
confidence remains average.

&&

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

Clear skies and cold temperatures have been the name of the game
for the past few days for much of Southcentral. The good news is
that temperature minimums have essentially bottomed out. 850mb
temperatures are starting to warm as the lingering airmass
radiates all the way out. Thus, temperatures across the region
will start to slowly rise again through the week. Tight
temperature and pressure gradients will maintain outflow winds
across Prince William Sound. Because of strong northeasterly
outflow winds and sub-zero temperatures through Thompson Pass, a
Wind Chill Advisory remains in effect today for the area. As the
aforementioned ridge shifts eastward into Southcentral later this
evening, the gradients along the sound start to relax and outflow
winds will slowly subside.

A surface low that is downstream of an upper-level trough will
track into the Gulf today and create impactful weather for Kodiak
Island. The island can expect to see a quick 3-6" of snow fall
across the region this afternoon into Tuesday morning. Winds with
this system aren't expected to be overly strong, however blowing
snow could occur and would reduce visibilities at times. Please
see the associated Special Weather Statement for more details.

A weak inverted trough will rotate through Prince William Sound
Monday evening into Tuesday, likely bringing several inches of
snow to Cordova, Valdez, and Thompson Pass. The Copper River Basin
is also on track to see some steady, light snow with this trough
from Monday night into Tuesday night. Uncertainty remains with
this feature and if it stalls in any one area, it could produce
several more inches over the current forecast.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Day 1 and 2)...

This morning, a front continue to track across the Bering and
towards Western AK. The leading edge of the precipitation shield
is forecast for later this morning and into the afternoon for the
Kuskokwim Delta and Bristol Bay. This system will bring a fresh
batch of snow to SW AK. Overnight blizzard conditions materialized
at St Paul and the expectation is that the blizzard conditions
will form along the coast. Blizzard Warnings for the potential of
gusty winds, reduced visibilities, and snowfall remain in effect.
The heaviest amounts of snow are anticipated along the coastal
areas. The models project snow making its way to interior
locations such as Bethel and Sparrevohn. Tuesday the low will have
moved into the Gulf Of Alaska taking the precipitation with it.
Tuesday will be dry across much of the region, although lingers
snow showers will be possible for the Alaska Peninsula. There is a
new low pushing across the Bering but it will not reach Nunivak
until late Tuesday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Day 1 and 2)...

Expect back to back lows for the Bering. A frontal system is
currently moving through the Central/Eastern Bering Sea. The
surface low anchoring this system is roughly 967 mb this morning.
This system will continue to bring widespread unsettled conditions
to the region. The front will push eastward reaching Bristol Bay
by noon. The blizzard conditions were observed at the Pribilof
Islands overnight and early this morning, and improvement is
expected today for the Pribs. As the front moves across the
Aleutians expect gusty winds, rain or a rain/snow mix. The high
for the state of Alaska yesterday was Adak at 50F, there is
definitely warm air associated with a portion of this system. The
models ping into the development a triple point low near the
Shumagin Islands as the dynamics shift eastward. The second low is
near Shemya this morning and that low will deepen as it pushes
north and east. Expecting gale forces winds with the potential
for storm force winds in the northern Bering. Aloft there are
multiple re- enforcing shortwaves. By Tuesday morning, the
trailing cold front will be over Adak with an occlusion over the
northern Bering.

&&

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

Gulf of Alaska: Expect winds less than 35 kts and seas less than
20 ft for the Day 3 through 5 period.

Bering Sea: A series of lows pass through the Bering in the long
term. A system moves into the northern Bering on Wednesday and
tracks towards the Bering Strait through Friday. Widespread gales
south of the low will persist through Wednesday evening before
dissipating. Another low moves over the Western Aleutians towards
the southern Bering Thursday night. This system will bring
widespread gales across the Bering and a chance for storm force
winds to the coastal waters of the Central/Western Aleutians
through Thursday night. Gales will persist through Friday. A
strong front off a Kamchatka low enters the western Bering Friday
night.

&&

.LONG TERM FORECAST (Days 4 through 7: Thursday through Sunday)...

Continual bombardment of low pressure systems traversing across
the Bering produce persistent active weather to Southern Alaska
through the long term. An elongated from extending off a low
tracking towards the Bering Strait on Thursday moves across
Southwest, resulting in widespread snowfall across the region. At
the base of the trough, near Kodiak Island, a surface low develops
and pushes towards the North Gulf Coast. There is some differences
between models as to how much remnant lingering warm air will
exist over Kodiak on Thursday, but the type of falling
precipitation will be highly depending on how warm the Island will
stay as the low passes. As per usual, the area that will likely see
the most snowfall will be along the North Gulf Coast and Prince
William Sound areas. In addition to those, widespread snowfall is
probable across the Susitna and parts of the Kenai Peninsula as
the low moves north. It is still uncertain whether or not the
Anchorage area will end up downsloped out.

Another low moves into the southwestern Bering on Thursday night.
It's front travels towards the Southwest Coast through Friday
afternoon before pushing onshore, seeking to bring yet another
round of widespread snow showers to Southwest before moving into
Southcentral with a repeated pattern. There is a stark difference
between the two systems, being the amount of warm air associated
with the second system looks to be significantly less than the
prior.

The front off the next system, a Kamchatka low, moves over the
Western Aleutians early Saturday morning. The GFS is the must
gung-ho with this system, hinting at widespread storm force
winds, heavy precipitation, and a significant warm air mass across
the Western and Central Aleutians. The EC/Canadian are not quite
as strong on the winds, with the Canadian only showing a small and
brief period of storms; but they are in agreement for the rather
intense warm air mass following the front and areas of heavy
precipitation along the front.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 155 161 195.
         Wind Chill Advisory 131.
MARINE....Storm Warning 178 185.
          Gale Warning 127 129-132 139 155 160 165 170 173-177 179-181
                       411-414.
          Heavy Freezing Spray Warning 119 121 125-132 136-141 160 165
                       180 181 185 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...AF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
MARINE/LONG TERM...SEB

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
256 PM AKST Mon Dec 13 2021

AKZ171-141200-
Kodiak Island-
Including the city of Kodiak City
256 PM AKST Mon Dec 13 2021

...ANOTHER ROUND OF SNOW AND BLOWING SNOW FOR KODIAK ISLAND...

A surface low will dive south of Kodiak later this afternoon
through Tuesday morning. This will bring snow accumulations of 3
to 6 inches across most of the island, to include Kodiak City. Due
to the track of the low, stronger winds gusting to 25 mph will
hug the southeast side of the island impacting the community of
Akhiok. Further north for Kodiak City, winds are only expected to
gust to around 15 mph. However, due to the dry, fluffy nature of
the snow, it could easily be blown around and reduce visibility
to under one mile at times.

There is still some uncertainty as to the exact track of the low.
If it ends up tracking any farther north, Kodiak City could see
a few more inches of snow and slightly stronger winds. Please
stay tuned into the forecast.