Small Craft Advisory 9, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
452 PM AKST Thu Jan 2 2025

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

Most of Southcentral remains cloud-free as a ridge of high
pressure persists over interior Alaska. The Copper River Basin
continues to experience temperatures 25 to 35 below zero, with
wind chills dropping to 30 to 50 below zero as optimal
radiational cooling, calm winds, and a robust arctic air mass
drives southward over the Basin. Additionally, cold temperatures
along with wind gusts up to 60 mph for Thompson Pass and keystone
Canyon will also produce wind chills as low as 50 below zero. Both
the Copper River Basin and Thompson Pass/Keystone Canyon will
experience these conditions through Saturday before the air mass
starts to retreat to the north. The rest of Southcentral will also
experience colder temperatures, with some places experiencing the
coldest conditions of the season to this point.

As an elongated low moves over the Copper River Basin and
stretches towards Southwest Alaska tonight, a pressure/thermal
gradient will form over the Alaska Range, Talkeetna Mountains, and
Chugach Mountains. Offshore-directed gap winds are expected
through Saturday, along with gustier conditions near Valdez, the
Matanuska Valley, Broad Pass, and Mentasta Lake down to
Chistochina. Valdez could experience gusts up to 40 mph tonight
while areas near Palmer and Wasilla could get gusts up to 60 mph
tonight through early Saturday.

By Saturday and continuing into Sunday, a weak trough is expected
to move north into the central Gulf towards the Southcentral
coastline and Kodiak Island. Light rain/snow will accompany the
trough as it lifts northward, however, models continue to struggle
with the timing of this system. What does look certain is that
most of the Gulf coastal areas will likely see precipitation.

-BS

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Tonight through Sunday night)...

A few updates have been made to the forecast, though the general
picture remains on track. Overall, continue to expect cold, dry,
and windy conditions for much of Southwest Alaska through
Saturday, with warmer, wetter, and windier conditions for the
Alaska Peninsula, Aleutian Islands, and Bering Sea. By Sunday, a
bit of a pattern change is looming as northerly flow ushers in
colder air for the Bering Sea, while southerly flow ushers in
warmer air for Southwest Alaska. Here are the hazards we're
monitoring:

* NEW: Cold Weather Advisory in effect for Lower Kuskokwim Valley
  (from Sleetmute to Lime Village) as wind chills could drop as
  low as -45 between Friday morning and Saturday afternoon.

* Heavy to extreme freezing spray off the sea ice edge from
  tomorrow night through the weekend.

* Potential for reduced visibilities in blowing snow for Bristol
  Bay and the Pribilof Islands, though confidence is low at this
  time.

Diving into the details... high pressure extends over Southwest
Alaska, while a gale force front extends across much of the Bering
Sea and Aleutian Islands. A few things to note with the front:
first, models have been stalling the front further south as its
parent low weakens and the ridge of high pressure over Mainland
Alaska remains robust. As such, some areas may see stronger winds
along the front persist for longer than initially forecast.
Secondly, the compact low that had been previously forecast to
move along the front has trended weaker in the latest model runs.
Instead of a closed low, the feature will likely be an open trough
instead. There's still uncertainty with the timing of this
feature, but there's decent confidence that storm force gusts
could graze Nikolski, the Central Aleutians, and Southern Bering
as the trough moves through. The final thing to note for the
marine forecast is the development of heavy to extreme freezing
spray along the ice edge and portions of the Southwest coastline
today as cold air filters in.

Speaking of cold, a Cold Weather Advisory (the new name for Wind
Chill Advisory) has been issued for Lower Kuskokwim Valley.
Confidence was high enough to issue the advisory, but it's not
quite a sure bet that wind chills will reach -40. Infrared
satellite this morning showed surface temperatures around -25
Celsius/-13 Fahrenheit for the advisory area (Sleetmute to Lime
Village). There is high confidence that temperatures will trend
even lower as cold air moves in from the interior. At the same
time, any winds that develop will disrupt radiative cooling,
warming up the ambient temperature. Still, even if air
temperatures are as "high" as -15 Fahrenheit, all it takes is a
stray gust higher than 15 mph to produce wind chills of about -40.
Wind chills could dip as low as -40 Friday morning, rise during
the day on Friday, then plunge even colder from Friday night
through Saturday morning. Temperatures should start to rebound
later on Saturday as warmer air moves in.

Several waves move across Southwest Alaska and the Eastern Bering
beginning Friday evening. Precipitation associated with these
waves, in combination with gusty winds from the tight surface
pressure gradient, could lead to areas of blowing snow. The
primary areas of concern, for now, are the Pribilof Islands and
Bristol Bay coast (from about Dillingham to Togiak). However, poor
model agreement and low forecast confidence means it's difficult
to assess blowing snow potential at this time. Similarly, as warm
air starts to move in later this weekend, there is potential for
freezing rain. Currently, that potential looks to be on the lower
end as temperatures should quickly warm to and above freezing for
the Alaska Peninsula and Bristol Bay. However, if models shift,
the likelihood of freezing rain could be greater than currently
forecast. Stay tuned as we continue to refine the forecast.

-Chen

&&

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

In the east the dominate pattern features a strong ridge of high
pressure over western Canada and a deep upper level low over the
Eastern Aleutians and AKPEN Peninsula. The upper level low will
gradual;ly migrate back over the Bering Sea as the week
progresses. This will flatten out the trough which will allow
several compact surface lows with triple point fronts to impact
the region through the end of the forecast period. Cool, dry air
will continue over most of interior Alaska. Active weather
occurring across the Southern half of the state will bring
successive strong southerly winds with high moisture inflow across
Southcentral Alaska with several transient lows. They will bring
fairly high frozen precipitation amounts to the upper levels and
mixed precip at the lower levels as temperatures gradually rise to
at or just above freezing.

A heavy bias was given to the GFS model in the near-term and an
even balance between the Canadian and European models in the 2nd
half of the forecast period.

In the West, a strong low in the North Pacific South of the
Aleutians brings rains to the Western and Central Aleutians with
gale force winds and snow over the Bering into Tuesday and
Wednesday. This North Pacific low moves away from Alaskan waters
South of the Central Aleutians through Thursday. Rain or rain and
snow mixed continue in the northeasterly gales that slowly
diminish over the Northern Bering through Thursday.

&&

.AVIATION...

PANC...VFR conditions and light northerly winds will persist.

&&