Small Craft Advisory 2, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
443 PM AKST Tue Dec 31 2024

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

Another calm and clear day for most of Southcentral, with some
notable exceptions. The closed upper level high continues to stall
at the border between the Yukon and Eastern Alaska border. This is
the reason for the colder temperatures, especially in the Copper
River Basin, and the widespread clear skies across Southcentral.
The Copper River Basin continues to be quite foggy with a strong
temperature inversion remaining prevalent. Weak upper level waves
are preventing the rest of the region from becoming foggy by
increasing cloud cover and mixing ever so slightly. One location
that has been gusty has been the Matanuska Valley. Palmer and
Wasilla have been going up and down in temperatures (from the
single digits to twenties) in a short period of time due to gusty
winds coming from the Glenn Highway allowing warmer temperatures
from above to mix down. Other gusty areas are the Valdez gaps and
passes including Thompson Pass. These areas are gusty due to a
temperature and pressure gradient between the Valdez area and the
Copper River Basin.

The more exciting weather is further south in Kodiak Island. The
low that has been advertised for a few days now has made its
closest approach to Kodiak Island and is now moving west towards
the Alaska Peninsula and the Aleutians. This is because the strong
high from before is blocking the low from moving any more to the
north. Kodiak is still experiencing moderate rainfall and gusty
winds of over 50 mph. The Kodiak Airport has received 0.77 in of
rain in the last 24 hours with higher elevations having received
even more. High-end gale force winds are being experienced in the
waters surrounding Kodiak Island including the Kamishak Bay and
Barren Islands regions. Shelikof Strait is experiencing storm
force winds. As the low continues its track to the west, wind
speeds will quickly diminish and will reach a minimum Tuesday
morning. Rain chances will also diminish, albeit more slowly.
Behind the low is a weak inverted trough that will pass through
Kodiak Island by Wednesday afternoon. Rain and wind speeds will
increase again in response, but not nearly to the same level as
before. Once all is said and done by Thursday, the whole region
from the mainland to to Kodiak Island will become quiet on
Thursday as high pressure and a col in the north Gulf influence
the region.

Friday will bring a change in the air mass. An Arctic trough will
drop from the north and force the high eastward. This trough will
drive temperatures down across Southcentral. This will create a
steep temperature gradient especially in-between Valdez and the
Copper River Basin. There is uncertainty exactly where the trough
will go, but if it passes by the Valdez region, very gusty winds
will happen in Thompson Pass, the Valdez gap regions, and even
Valdez itself due to steep pressure gradients. The rest of
Southcentral including Anchorage could see the coldest air since
November. Again, this will all depend on the track of the Arctic
trough, but a colder weekend is highly likely. This will be a dry
air mass so little to no precipitation is expected. Though a weak
upper level wave will slowly move up the Gulf, so some rain in
Kodiak Island may be possible by the end of the period with
moisture potentially making into the Gulf coast afterwards.

-JAR

&&
.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: This afternoon through Fri afternoon)...

Two lows and their fronts will bring active weather across the
region as we head into the new year. For much of Southwest Alaska,
expect breezy conditions, with the weather trending drier and
colder towards the end of the work week. For Alaska Peninsula and
the Aleutian Islands/Bering Sea, expect wetter conditions (mostly
rain) and winds to gale force as a front sweeps through on
Thursday and Friday. Here are a couple hazards we'll be
monitoring:

* Strong easterly winds, with gusts of 50-60 mph possible, for
  Unalaska from Thursday afternoon through Friday as the front
  moves through

* Wind chills as low as -20 to -30 for Kuskokwim River
  communities, from Thursday night into Friday

* Heavy to extreme freezing spray off the ice edge near Nunivak
  Island, from Thursday night into Friday

Diving into the details... a low slides westward along the Pacific
side of the Alaska Peninsula and Eastern Aleutians through
Wednesday night. Strong winds have been the most notable weather
associated with this storm. Winds have been quite gusty across
much of Southwest Alaska, with many areas seeing east to
northeasterly gusts of 25-35 mph. The strongest gusts since
midnight have been at King Salmon and Pilot Point, where favorable
gaps in the terrain have allowed for gusts to 47 mph. Winds will
gradually diminish from tonight through tomorrow morning as the
low weakens, but expect generally breezy conditions to persist
for all but Kuskokwim Valley through the end of the week.

In addition, a band of precipitation associated with this low is
currently bringing light snow and rain to the Kuskokwim Delta
coast, with virga over the Bristol Bay coast. As the band rotates
westward through tonight, precipitation will shift towards Nunivak
and Pribilof Islands. For Alaska Peninsula and the Eastern
Aleutians, expect persistent showers through tomorrow evening as
the low lingers in the vicinity, with another round of showers on
Thursday as a shortwave enters from the Gulf.

Beginning late Wednesday afternoon, a broad, occluding low will
push its gale force front across the Western and Central
Bering/Aleutians. Models are in decent agreement with the front,
but there is some uncertainty with this feature. First, if compact
lows develop along the front, they may produce localized areas of
winds up to storm force. For now, it's difficult to pinpoint
whether (and where) these compact lows may develop. Secondly,
there is some question of how far east the front may progress.
This will depend on how strong the ridge of high pressure is over
Mainland Alaska. While Southwest Alaska looks unlikely to see any
precipitation associated with this front, how far east the front
moves will ultimately affect the surface pressure gradient in
Southwest Alaska, which will then affect wind chills and freezing
spray severity off the ice edge. Stay tuned as we continue to
refine the forecast.

-Chen

&&

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

A broad upper level low stretches from Eastern Asia across the
Bering into Western Alaska through the forecast period. This low
area will be meandering around the Bering through next week. Most
of the Arctic regions remain under an equally broad upper level
ridge, while another ridge over Southeast Alaska and Western
Canada sets up over most of Interior Alaska. Temperatures as low
as 40 below are expected across the upper and Central Copper River
Valley Saturday and Sunday. The Gulf of Alaska section of the
ridge helps sustain deep onshore flow from the Alaska Peninsula
and Kodiak Island across the Southcentral coastal zones through
the weekend.

Transitory North Pacific lows and fronts will bring some moderate
rains from the Eastern Aleutians to the Canadian border through
Tuesday. Areas away from the coast will remain cold enough to add
some additional snow. A strong North Pacific low Monday will
spread heavy rain and gusty winds across the Gulf with winds
approaching gale force near Kodiak Island. Affected rain areas
include from the Eastern Aleutians, AKPEN/Bristol Bay and
Southwest Alaska to Kodiak Island and Prince William Sound over to
the Canadian border through Tuesday. This low will sweep Westward
over the Shumagin Islands for Tuesday. In the West, a moderately
strong surface low and its elongated front press along the Western
and Central Aleutians spread locally heavy rains and gusty winds
through the period. The pressure gradient across the Bering
combined with outflow winds from Western Alaska will be sufficient
for widespread gale force winds over the Central and Western
Bering through Monday morning, diminishing Tuesday.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist. Expect
northerly wind from Knik Arm to continue through the period.
Mid-level clouds may increase for a brief period Wednesday
morning.

&&