Brisk Wind Advisory 74, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
459 AM AKST Wed Dec 27 2023

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

A weak shortwave rotating north around a deep upper level low
pressure system over the Bering Sea will push north of the Gulf of
Alaska Coast this morning and into the Copper River Basin this
afternoon. This will continue the diminishing trend for the scattered
snow showers that are currently found in the northern Gulf of
Alaska and Copper River Basin. Weak high pressure is building in
behind the wave and as skies begin to clear out, freezing fog is
developing over Cook Inlet and will drop ceilings and visibility
through the morning before lifting this afternoon. In locations
away from Cook Inlet where fog is not forming, the light winds and
clearing skies are producing cold temperatures. Temperatures have
fallen into the negative single digits and lower teens below in
the Susitna Valley and are in the single digits and teen below in
the Copper River Basin. Single digits above and below are found in
the Anchorage Bowl, the Western Kenai Peninsula and the Matanuska
Valley while teens and lower 20s are found along the Gulf of
Alaska coast.

As the weak high pressure builds into the area, expect a few
peeks of sun for most locations today, with isolated snow showers
especially to the east and north of Prince William Sound. Winds
will be light over inland areas while strong and gusty off shore
winds will continue through bays and gaps including the Copper
River Delta.

High temperatures today will be in the single digits to lower
teens above in inland locations and in the teens to 20s for
coastal locations. Cold conditions are expected again tonight as
skies remain mostly clear and winds remain light especially in
inland areas. Low temperatures tonight will drop into the single
digits and teens below in the Susitna and Matanuska Valleys and
mainly into the single digits below on the Western Kenai Peninsula
while the Copper River Basin will drop into the 20s below with a
few 30s below not out of the question for typical cold spots. East
Anchorage will likely drop to near 10 below. High temperatures on
Thursday will be in the single digits above to the lower teens
for most inland areas while highs in the 20s are expected Thursday
for coastal locations.

CC

&&

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

The main features for Southwest Alaska continue to be the trough
over the northern Bering and a few weak shortwaves moving over the
Alaska Peninsula. Snow showers will continue throughout Southwest
with the exception of near the western Alaska Range and northern
portions of the Aleutians, where dry and sunnier conditions are
expected. Overall the band of showers that was expected to
develop along the northern Bristol Bay coast has not come to be as
impressive as guidance indicated, but additional light
accumulation of a couple inches is possible. The showery pattern
will come to a close Thursday morning as a broad, complex low
moves into the Bering and builds heights over Southwest. Shortwave
ridging and offshore flow will lead to a return of clearer skies
and cold temperatures.

-Jones

&&

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

A very complex pattern is evolving over the Bering as a strong
front moves over the Chain tonight. Due to ample cold air
currently over the Bering, precipitation type along the leading
edge of the front is expected to be snow. Winds and precipitation
will hit Shemya early this afternoon with winds gusting as high
as 65 mph with falling and blowing snow. The air temperature near
32 degrees will be the hindrance of a true blizzard on the ground,
but the snow will be falling sideways in the strong wind, leading
to visibility of one quarter mile or less this afternoon and
evening.

Frontal precipitation will reach Adak around 9pm, with strong
south to southeast winds gusting around 60 mph. Precipitation type
forecast with this front is tricky for the Central Aleutians.
Temperatures aloft aloft are cold, around -8C at 850 mb, but the
strong southerly winds will support temperatures around 34 degrees
near the surface. Forecast thinking currently is that snow is
expected at the onset, and it will mix with and change over to
rain later in the night for both Adak and Atka. During the period
of snow, expect visibility reductions of one half mile or less at
times. Snow levels are forecast to be around 100 to 200 ft.

Throughout the day on Thursday multiple lows are expected to
develop along the front, leading to areas of high end gales to
storm force winds. As the system spreads out and becomes a complex
low, temperatures will continue to warm.

-Jones

&&

.LONG TERM FORECAST (Days 4 through 7: Friday through Tuesday)...

The beginning of the long-term period is defined mostly by a
large, complex low pressure system over the central Bering Sea and
a weak trough swinging into the northern Gulf of Alaska. In the
Gulf, the weak trough is expected to enter Prince William Sound
and interior Southcentral Alaska by Friday afternoon/evening. This
will result in likely showers along the coastline with some
moisture pushing into interior Southcentral possible. In the
Bering, the complex low pressure system is suffering from a large
spread in model solutions. This makes tracking where individual
cells, and the progression of the entire system difficult. It does
appear that a frontal boundary will be over the central/eastern
Aleutians and will be advancing eastward, moving into Southwest
Alaska for the weekend. The Pribilof Islands will likely see an
extended period of snowfall from Friday into the next work week.
The remainder of the Aleutian Chain will likely see showers
through the weekend. Details on where low centers establish within
the complex will become more clear as we approach the end of the
week so stay tuned for updates.

&&

.AVIATION...

PANC...Lingering patchy stratus around Cook Inlet and the
Anchorage Bowl will occasionally move over the terminal through
the morning, dropping ceilings from VFR to MVFR at times. Some
potential remains for patchy morning fog due to low-level
moisture from last night's snowfall as well as a temperature
inversion aloft. However, thinking IFR conditions less likely
today than yesterday given that the inversion is higher off the
ground; this should allow moisture to move higher into the
atmosphere rather than being trapped at the surface.

By late morning/afternoon, light northerly winds and a return to
VFR conditions, though patchy radiation fog and low stratus
remain in the forecast as skies clear tonight.

-KC

&&