Heavy Freezing Spray Warning 221, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
538 AM AKST Fri Dec 10 2021

.ANALYSIS AND UPPER LEVELS...
A stacked low remains over the northern Gulf this morning with
its occluded front lifting inland of the coast. Convergence near
the stacked low's center is promoting snow from Cordova to
Whittier along with additional snow from Seward to Kenai on the
backside of the low and where cold air advection is dropping
temperatures along the northwest Gulf down to at or below
freezing. These colder temperatures in combination with smaller
shortwaves diving south across the Alaskan Peninsula are promoting
widespread gales over the Bering and through the Aleutian Chain.
A blizzard warning continues for areas south of King Salmon where
blowing snow will result in reduced visibility at or below three
quarters of a mile. As cold air continues through the gaps and
passes and into the Pacific side of the Alaska Peninsula, storm
force winds will become more common out of the gaps and passes
through Friday. Hurricane force winds and higher gusts are
expected on Saturday from the Kamishak Bay gap to west of the
Barren Islands. Otherwise, over the next few days Alaska will once
again flex its icy grip with 850 mb temperatures of -25 to -30
degrees Celsius to gradually overspread much of the state by
Sunday. Locations such as Anchorage will see overnight lows in the
minus teens and locations across the Copper River Basin could see
overnight lows in the upper twenties below zero.

&&

.MODEL DISCUSSION...
Models are in good agreement through the next next 48 hours. An
arctic air mass is on tap to overspread much of Southwest and
Southcentral through the weekend and guidance depicts this
scenario reasonably well.

&&

.AVIATION...
PANC...MVFR conditions briefly developed this morning but have
since risen back to VFR. Numerical guidance suggests VFR
conditions will prevail through tonight and into Saturday. This
appears more than reasonable as a stacked low near the Gulf coast
tracks away to the southeast and the current air mass over PANC is
replaced by increasingly drier air instead.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: Today
through Friday Night)...

As the current storm impacting Southcentral begins to wind down,
all attention will then turn to the much colder air mass working
its way into the area. As the cold air mass moves in, strong
winds will accompany it for a number of communities.

Currently, the center of the low impacting southcentral is moving
east to the south of the southern tip of Montague Island.
Associated snow continues across Prince William Sound and adjacent
coastal communities, and the easterly flow north of the center is
slinging that moisture into the Kenai Mountains. As such, the
Winter Storm Warning for the eastern half of the peninsula has
been extended until noon; after which point the center will be
far enough east that snowfall rates will be rapidly diminishing.
Meanwhile, a deformation band of steady light to moderate snow is
aligned right along the coast of Cook Inlet from Nikiski to
Ninilchik. This band is nearly stationary, and so that snow will
continue into the morning. Fortunately, winds in the area have
largely diminished, so blowing snow will only be a concern in the
wake of vehicles. The snow band is expected to largely weaken in
place through this morning, but since it's impacting a large swath
of the Seward Highway, the Winter Weather Advisory remains in
effect until noon.

The low will begin to sink southward into the Gulf and away from
Southcentral this evening. In the wake of the low, a full Arctic
blast will follow in the form of strong gusty winds and falling
temperatures. The winds will help to delay the onset of the
coldest temperatures, and as such, temperatures broadly speaking
the next couple days have been raised a few degrees. That said,
the winds will certainly not make it feel much warmer.

High wind potential will once again turn southward towards Kodiak
Island tonight into Saturday morning. As the core of the coldest
air squeezes through the gaps in the mountains, an upper level
disturbance will enhance the winds, particularly late tonight
through Saturday morning. Thus, while the High Wind Warning for
Kodiak Island has expired, with Akhiok verifying the warning with
65 kt/75 mph gusts last night, residents should still prepare for
another round of similar strength winds but with falling
temperatures again tonight.

The very cold air and strong, gusty winds will also pose a
significant threat to marine traffic this weekend in the form of
heavy freezing spray. The areas where it will be the most extreme
will be through southern Cook Inlet, the Kennedy Entrance, Barren
Islands region, and southward through Shelikof Strait. These will
be the areas getting the strongest cold advection with the core of
the coldest air moving through that area in combination with the
strongest winds and the aforementioned upper level disturbance
further increasing the winds. However, heavy freezing spray will
be prevalent across all the rest of Kodiak Island, Marmot and
Chiniak Bays, all of Cook Inlet, and along the Gulf coast of the
Kenai Peninsula. Mariners should use extreme caution if traveling
through these waters for all of this weekend.
The other notable, but far less impactful effect of the very cold
air and strong gusty winds will be wind chills, which may approach
40 below through the Broad, Isabel, and Mentasta Passes this
weekend. Everyone across Southcentral should prepare for this
latest round of very cold wind chills Saturday night and again on
Sunday night. Finally, the gusty winds will likely resuspend some
of the recently fallen snow through the gaps as well, causing
localized reductions in visibility.

The bright side to this forecast is that once the snow ends later
today across coastal regions, a period of dry weather will take
hold and persist through at least Monday, with the next round of
light snow on track to impact nearly all of Southcentral Monday
night through the day on Tuesday. While it may take until late
Saturday or Sunday to get full mid-December sunshine (such as it
is) back, sunnier skies are on the way!

&&

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

The longwave pattern features a deep trough axis that spans over
Mainland and into the Central Bering. There are a series of
shortwaves from NE Russia to the Alaska Peninsula. While the 500
mb closed low is over the Gulf Of Alaska, embedded shortwaves
wrapped in that feature will push over Southwest AK providing the
dynamics for snow showers. At the onset of the forecast period
there is a tight pressure gradient in place; expect gusty winds. A
Blizzard Warning remains in effect until 5 PM AKST for areas south
of South of King Salmon and along the Alaska Peninsula. Northerly
flow will persist into Sunday. Colder air will usher into the
region as lows will be 10 to 20 below zero and possibly colder in
some locations. Heavy freezing spray will impact Bristol Bay and
K-Bay.

&&

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

The longwave pattern features a deep trough axis that spans over
Mainland and into the Central Bering. As the forecast period
advances, ridging will build over the Western Bering. With the
trough to the east and the ridge to the west, expect the winds to
remain northerly for much of the region. There are a series of
shortwaves from NE Russia to south of the Alaska Peninsula.
Convective snow showers will develop over the Bering. As cold air
advection strengthens late Friday into Saturday expect robust wind
gusts through the gaps and passes. There is a compact low in the
western Bering that will weaken Saturday and become absorbed into
the longwave pattern. As the upper ridge shifts eastward a new
Pacific low will move toward Attu on Saturday and Sunday.

&&

.MARINE (Days 3 through 5: Sunday thru Tuesday)...

By Sunday morning, the powerful low that is currently near
mainland Alaska will have moved south of the Gulf of Alaska, but
there will still be a strong pressure gradient from the ALaska
Peninsula through the Barren Islands resulting in Gales-to-storm
force winds across this area on the Pacific side of the Peninsula
and into the western Gulf of Alaska. These Northwesterly winds
will also likely bring widespread freezing spray and Heavy
freezing spray to these areas. These winds should diminish
Monday easing the freezing spray situation at that time.

The next system will move into the western Bering Sea early
Sunday and spread through the rest of the Bering Sea by Monday.
Storm force winds are expected with this system in the northern
half of the Bering Sea with Hurricane-force winds possible in the
northwest portion of the Bering on Monday.

&&

.LONG TERM FORECAST (Days 4 through 7...Monday through Thursday)...

A progressive pattern remains over the Bering as a ridge of high
pressure slides east in response to a deepening shortwave trough
that crosses the Bering Sea and the Aleutian Chain. A rapidly
intensifying surface low near Kamchatka and a leading front will
bring widespread precipitation, strong winds, and elevated seas
through Tuesday. Compared to previous model runs from yesterday,
the consensus has trended to take the low southeastward of the
Alaska Peninsula by early Tuesday. The exception will be a frontal
wave breaking off the low that will bring coastal rain and
mountain snow for the southern-southwestern mainland for late
Monday into Tuesday. Another low will move across the Bering and
Aleutians for the middle of next week with a continuation of winds
and precipitation. Models deviate, however, on the exact track
and position of this system but are nonetheless keying on an
active weather pattern to persist from the Bering to the Gulf. For
Southcentral, benign conditions will prevail with a surge of
Arctic air spilling across the Alaska mainland. Much below normal
temperatures can be expected once again across the southern half
of the state on Monday with some improvements for the middle of
next week. Meanwhile, the packing of cold air over the coastal
mountains and tightening pressure gradient will likely keep
localized winds funneling through the gaps and passes.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...
Blizzard 161.
Winter Weather Advisory 121.
Winter Storm Warning 125.
MARINE...
Gale 120-121 127-129 136-137 170-173 175-176 178-181
185 412-413.
Storm 131-132 138 150 155 174 352.
Hurricane Force Wind 130.
Heavy Freezing Spray 120 129-132 136-140 150 160 165 180-181 185
352 414 .

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
MARINE/LONG TERM...EZ/MF

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
330 PM AKST Fri Dec 10 2021

AKZ181-111400-
Alaska Peninsula-
Including the cities of Cold Bay and Sand Point
330 PM AKST Fri Dec 10 2021

Widespread snow showers and strong northwesterly winds will
continue through Saturday night. The blowing snow in these snow
showers combined with the strong winds will result in
significantly reduced visibility at times through Saturday night.
Snow shower activity will decrease on Sunday morning and will
allow for visibility to improve.