Gale Warning 12, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
549 AM AKST Sat Jan 4 2025

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

Discussion:

While cold temperatures continue to linger over the Copper Basin
this morning, there has been some improvement as cloud cover has
been steadily increasing over the Gulf and into inland Southcentral.
Temperatures have steadily increased and are currently sitting in
the mid to upper 20s below zero with apparent temperatures in the 30
to 40 degrees below zero. However, any clearing of cloud cover will
result in temperatures quickly dropping. The increase in cloud cover
combined with gusty Mat Valley winds have kept temperatures up
around Palmer and Wasilla, and even down the Knik arm towards
Anchorage, where temperatures are generally in the teens. Mat Valley
winds should slacken some today as the gradient starts to relax;
however, a system moving north into the Gulf will allow for
increasing down inlet winds resulting in a steady northerly wind
from the Mat-Su Valley southwards.

With temperatures warming and gap flow winds decreasing, we turn our
attention towards what appears to be a parade of lows lifting
northwards out of the North Pacific over the next week. Model
agreement is good in this shift in pattern, but it is anyone's guess
as to where each of these lows will track...more specifically
towards midweek and beyond. What we do know is that this shift in
pattern will be more favorable for precipitation, potentially heavy
at times, over the next week. With this said, we will see the east-
to-west oriented elongated trough over central Alaska continue to
shift west today as a trough lifts north over the Gulf.
Precipitation will spread westward through the day today, with
Cordova and Prince William Sound seeing precipitation first then
moving into the eastern Kenai Peninsula. Kodiak will also start to
see more steady precipitation by early to mid afternoon. Most of the
forecast area, including coastal areas of the Kenai and Prince
William Sound, remain cold enough that the initial wave of
precipitation will likely remain all snow.

The main trough will lift across the Gulf tonight through Sunday
morning dragging warmer air north. With this wave we will start to
see more chances of a wintry mix of freezing rain, snow, or a
rain/snow mix before changing over to all rain for lower elevations
along the Gulf coast. Higher elevations should remain snow to start
but snow levels look to increase between 1500 to 2500 ft for the
Kenai and Chugach Mountains by Monday. Models seem to be in good
agreement with timing and placement of the system up to this point.
However, both the Canadian and GFS are favoring a compact low
rapidly lifting up towards Kodiak Island Monday. There are still a
lot of details to iron out given tricky temperature profiles and
model inconsistencies over the next several days, so continue to
monitor for the latest forecast updates for your location.

- PP

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Saturday through Tuesday morning)...

Hazards we're currently monitoring include:

* Heavy to extreme freezing spray through Sunday, with the most
  dangerous conditions expected within 20 nautical miles from the
  ice edge from south of Nunivak Island to St. Lawrence Island.

* Periods of reduced visibility due to blowing snow for the
  Pribilof Islands (Saturday afternoon through Sunday) and along
  the Bristol Bay coastline from Dillingham to Togiak (Sunday
  morning through the afternoon).

* Potential freezing rain from Sunday night through Monday, as a
  warm and very wet weather system barrels into Southwest Alaska
  from the North Pacific.

An unsettled pattern continues as several lows lift out of the
North Pacific and across Southwest Alaska through Tuesday.
Forecast confidence remains a bit lower than usual as models
struggle to come to a consensus on the strength and track of these
systems.

For the Bering Sea and Aleutian Islands, light precipitation
continues through the weekend as a trough axis, extending the
length of the Aleutian Island Chain and roughly parallel to it,
rotates to a north/south orientation by Tuesday. Synoptic scale
flow will remain counterclockwise around this feature through the
weekend. At the western end of this trough, a 965 mb low center
will drift southward into the North Pacific through Tuesday,
drawing colder, northerly flow behind it. Meanwhile at the
eastern edge of the trough, a northward moving 973 mb low reaches
the western AKPen Sunday morning, and a second 980 mb lobe, which
extends over Kodiak Island, takes until Monday morning to reach
Southwest.

These features bring warm, moist air that is expected
to interrupt the stream of cold air from the interior and
moderate temperatures through the week. Expect rain to mixed
rain/snow for the AKPen and communities near Bristol Bay but
south of Dillingham, and snow for the Pribilof Islands and
communities north of Dillingham.

&&

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

Very little change from yesterday with minor edits for timing.
High confidence in the major pattern shift but low confidence in
system tracks and precipitation amounts and types.

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
gradually 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.

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 Friday. Rain or rain and
snow mixed continue in the northeasterly gales that slowly
diminish over the Northern Bering through Friday.

Inconsistent model guidance is the real challenge in the upcoming
week. GFS and Canadian models do well in days 4 and 5. GFS
becomes the outlier in days 6 and 7 where the European and and
Canadian models seem to perform only slightly better.

DD

&&

.AVIATION...

PANC...VFR conditions will persist through the TAF period.
Northerly winds of 10 to 15 knots with an occasional gust up to 20
knots will also persist through the TAF period. A series of fronts
will lift northward through the Gulf and to the coast this
weekend. While the terminal should remain mostly dry due to
cross-barrier southeasterly flow, a few snow showers could make it
across the mountains and over the terminal; especially tonight
while flow across the mountains is still somewhat weak.

&&