Heavy Freezing Spray Warning 21, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
528 AM AKST Thu Jan 6 2022

.ANALYSIS AND UPPER LEVELS...

At 500 mb there is a strong high over Siberia that spans into
Alaska and the Yukon Territory. There are closed lows south of
Shemya and near Adak. That high will influence the track of the
lows coming out of the north Pacific. On nighttime microphysics
satellite imagery there is fog over portions of Turnagain Arm, an
occluded front over Kodiak and the remnants of a frontal boundary
near Dutch Harbor. The high for the state was 45F at Dutch Harbor
and the low for the state was -55F at Northway.

&&

.MODEL DISCUSSION...
The models are in good agreement with the synoptic pattern for
Thursday and Friday. The models remain on track bringing a fetch
of warmer and moister air aloft into Southcentral this weekend.
The primary forecast challenge will be pin pointing the
precipitation type.

&&

.AVIATION...
PANC...VFR conditions expected this TAF package. Winds will
remain northerly. Next chance for precipitation at PANC will be
Saturday.

&&

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

The upper-level ridge that was in place over the interior is
beginning to push to the south and west as a polar low dives south
from the Beaufort Sea. This feature will keep conditions mainly
clear and cold across interior Southcentral through into the
weekend. However, as this upper-level low moves over the Canadian
Arctic, it will eject a series of upper-level shortwaves south
across the region. The first of these will move through overnight
Thursday and begin the push of colder air aloft back over the
Copper River Basin. This wave will also allow gap winds across
Prince William Sound to increase once again, as well as develop a
surface trough or weak low near Middleton Island.

A second, more potent wave will race south on the heels of the
first, reaching the Southcentral coast late Friday. 850mb
temperatures across the Copper River Basin (~4,500 ft AGL) will
drop quickly from -12C late Thursday to -18C Friday morning and to
near -30C by Saturday morning. By Saturday, the aforementioned
upper-level wave will stall, then slowly retrograde west as a
ridge builds in advance of another storm system lifting toward to
the western Gulf from the North Pacific. This retrograde motion
will help steer the surface low back toward the Barren Islands
with another round of light snow possible for the eastern Kenai
Peninsula and Kodiak Island.

An increase in northeasterly winds, especially for the Matanuska
Valley, will be the bigger focus, though. As the upper-level wave
drops south, a northeasterly flow will develop not only near the
surface, but aloft. This wind flow, coupled with the synoptic set
up and arctic air building over the Copper River Basin, will once
again bring a sharp increase in winds across the valley beginning
Friday afternoon. These winds will likely peak late Friday night
then diminish slightly overnight as the wave slides west and the
flow aloft becomes more easterly. However, as stated earlier, this
will move the surface low to the Barren Islands and allow the
pressure gradient between it and the building surface ridge over
the Al-Can border to tighten. Given the northeast to southwest
orientation of these surface features, an increase in winds is
again expected for Saturday and should continue into Sunday as
this gradient holds, aided by a frontal system moving into the
northern Gulf.

While gusty winds are expected for locations such as Palmer and
Wasilla, these gusts are currently not expected to be nearly as
strong as the previous wind event. The reason is twofold. First,
the upper-level support is not quite as strong as with the
previous system. Second, the pressure difference between the
surface features is not as great. Nonetheless, given the dynamics
and the amount of cold air pooling in the Copper River Basin,
wind gusts as high 45 to 60 mph Friday afternoon through early
Sunday are not out of the question. Stay tuned to forecast
updates as there is still some model uncertainty as to how this
event may play out.

By late Saturday into early Sunday, a front associated with a low
well south of the AKPen will lift into the Gulf. Snow is expected
to move across Kodiak Island, changing to rain along the eastern
coast as an easterly flow advects warmer air in from the Gulf. The
front then moves to the coast with snow expected along the coast
as well as an increase in northerly gap winds across Prince
William Sound.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Day 1 through 3: Today
through Saturday)...

Clear, cool, and dry conditions will persist through the end of
the week as zonal flow aloft gives way to weak upper high pressure
by Friday. A North Pacific low will track farther northward by
Friday evening, tightening the pressure gradient and thus
increasing northeasterly winds over the Kuskokwim Delta and
central Bristol Bay. Scattered precipitation is also possible by
Saturday over Bristol Bay as the low continues its northward track
and elongates. However, its exact position any resultant
downsloping near the Alaska Range remain uncertain at this time.
In any case, any rain/snow would be of little/no impact until
possibly later in the weekend.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Day 1 through 3:
Today through Saturday)...

A low tracking northward near the western Aleutians will bring
rain and gusty southerly winds today. Southeasterly flow to its
east will allow for highs to reach the 40s over the central
Aleutians. Two lows will merge over the North Pacific Friday into
Saturday. Much of the precipitation looks to remain south of the
Chain until later in the weekend, although gusty northeasterly
winds are possible near the Alaska Peninsula.

&&

.MARINE (Days 3 through 5 - Saturday through Monday)...

Aleutians / Bering...Broad high pressure retreats to the Russian
Arctic by Monday. An elongated area of low pressure remains South
of the Aleutians, weakening over the Western Aleutians for Monday.
Forecast confidence decreases by the end of the period.
Widespread Easterly gales spread across the Aleutians and Bering,
becoming Northerly over the Central and Western Aleutians and
Bering by Monday. Seas building to 22 feet over the Bering Sunday
and Monday. Increasing risks for freezing spray over Western
Bering open waters through Monday. A North Pacific low moves
across the Alaska Peninsula Sunday to the Central Bering for
Monday.

Gulf of Alaska...A North Pacific low moves over the Alaska
Peninsula South of Kodiak Island Sunday. Forecast confidence is
mixed based on the low's track and timing. Gusty winds increase to
widespread high end gales with boundary jets storm force winds
along the Gulf coasts, diminishing late Sunday. Seas building to
22 feet over the Gulf for Sunday, subsiding Monday.Increasing
risks for freezing spray over open waters of Cook Inlet and
Kachemak Bay on Sunday.

&&

.LONG TERM FORECAST (Days 4 through 7/Sunday through Wednesday)...

Looking ahead into the extended forecast, the latest operational
model runs are slowly coming into agreement with the evolution and
progression of the synoptic scale features for the weekend but
diverge in the specific details towards the end of the period. A
blocking ridge extending from the northern Bering Sea to eastern
Siberia will continue shifting westward on Sunday, while a trough
with an embedded low retrogrades westward across the Alaska
mainland and into the eastern Bering Sea. Meanwhile, this low will
eventually phase into a broader trough to the south of the
Aleutians, with increasing southerly winds drawing a deep fetch of
tropical moisture across the Bering into the Gulf. For Sunday
through Tuesday, models seem to key on a frontal boundary
extending from a center of a low, bringing precipitation from
Kodiak Island northward to the Alaska Peninsula, and into the
southern mainland. Where the uncertainty emerges is the track,
position, and timing of subsequent surface lows circulating
upstream of the main trough, but overall are trending toward a wet
and unsettled pattern to persist. Additionally, a tightening
pressure between the retreating high to the north and low pressure
in the Gulf will create conditions favorable for windy
conditions, especially through the gaps and passes. Increasing
moisture and cloudiness will also help with the much below normal
temperatures over the last several days to rebound across much of
the coastal areas and interior valleys.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...131 Wind Chill Advisory.
MARINE...Gale 150 172 173 174 175 176 177 178 179 185 411 412 413
121 125 127 128 138. Heavy Freezing Spray 119 121 126 127 128 129
130 139.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...KZ/MF

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
223 PM AKST Thu Jan 6 2022

AKZ111-071130-
Matanuska Valley-
Including the cities of Palmer, Wasilla, Sutton, and Chickaloon
223 PM AKST Thu Jan 6 2022

...STRONG WINDS FRIDAY AFTERNOON THROUGH SATURDAY...

Strong northeast winds sustained 25 to 40 mph, with gusts of 45
to 60 mph will return Friday afternoon and continue through the
overnight hours before slowly diminishing Saturday morning. There
is also the potential that winds will increase again late Saturday
afternoon before diminishing Sunday morning. Loose debris may
still be blown about by these winds and should be secured where
possible.

Wind chills from 15 to 30 below zero are expected with higher
winds. This could cause dangerous life-threatening conditions for
those without power, as frostbite can develop in as little as 15
minutes in these conditions.

For the latest information, visit us at: weather.gov/anchorage.