Blizzard and High Wind in Alaska, December 4 to 7, 2023

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
430 AM AKST Mon Dec 4 2023

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

The quiet weather pattern for Southcentral Alaska is coming to an
end as a 958 mb low in the Northern Pacific lumbers slowly into
the Southern Gulf of alaska today, and into the Central Gulf of
Alaska on Tuesday as a 965 mb low and into the Northern Gulf of
Alaska on Wednesday as a 982 mb low and finally makes landfall
just east of Prince William Sound as a 992 mb low on Thursday
morning.

Expect northerly gap winds continue this morning and through the
day as well as gales to develop in the marine areas of the
northern Gulf this morning. Radar continues to show an increase in
precipitation along the north Gulf coast this morning. With the
slow moving low only inching northward and remaining out over the
Gulf, cold air will remain entrenched near the surface over inland
Southcentral. As a result, gap winds remain persistent around the
same intensity through at least Wednesday if not into Thursday.

On Tuesday, a relatively weak, neutrally-tilted trough pushes in
over Western Alaska, drawing north mid-level moisture from the
low in the Gulf and bringing snow to portions of Southcentral
Alaska. The strength and progression of the trough will determine
how it interacts with the Gulf low. With significant spread in
how the models depicting this interaction, there is significant
uncertainty in where the axis of precipitation ultimately sets
up. The current most likely scenario puts the band of precipitation
over the Copper River Basin, with a focus toward the western
half. With cold air persisting inland, this could fall as
potentially up to 6 inches of snow through Wednesday afternoon.
Higher amounts will be possible in the southern Copper River Basin
& Thompson Pass, where more moisture is wrung out over the
coastal mountains. Blowing snow is likely to be an additional
hazard for Thompson Pass as cold air continues to filter out
through gaps. While the forecast does not explicitly depict snow
accumulation west of the Chugach Front Range and Talkeetna
Mountains, there is a moderate chance that the edge of the
precipitation will extend far enough west for some amount of snow
to fall in Anchorage and parts of the Mat-Su Valleys.

By Wednesday, the low moves into the northeastern Gulf, drawing
cold air across the Western Alaska Range. This cold air advection
is likely to enhance gap winds in the western Gulf to borderline
storm force. For Wednesday evening, this may begin to push
precipitation eastward and eventually clear it out of
Southcentral.

CC

&&

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

No major changes to the forecast at this time. See previous
discussion; the forecast remains on track:

Snow showers between Pilot Point up towards Togiak and Aniak and
Bethel will continue to linger into this morning. It will take a
little longer for the snow to diminish for the Alaska Peninsula,
where snow should end by Monday evening. An additional 1 to 4
inches in expected with higher amounts closer to the mountains. As
the trough weakens and a large low pressure system moves into the
Gulf, cold air will filter from north to southeast across the
Alaska Peninsula Monday. Temperatures will likely trend cooler
across the Southwestern Interior and spreading westward to the
coast through the entire week. High end gale force winds with
gusts to around 50 to 60 kts through bays and passes, between the
Shumigan Islands and Kodiak Island. Wide Bay and Chignik area will
continue to ramp up their winds on Wednesday.

Out across the Bering, a developing low with bring a robust front
will move into the western Bering after midnight. Winds ahead of
the initial front from 10 to 20 kts will quickly become disrupted
with gale force winds just behind the front. Another low will
follow quickly behind and keep gale force winds in the
northwestern Bering and across the entire northern Bering through
Wednesday. Considering NAM as an outlier going into Tuesday night
and Wednesday, the majority of other lows are tracking further
north of St Matthew Island toward St Lawrence. Should the low
track further north, it could bring a brief period of slightly
warmer temperatures more northward and also have slight changes in
the wind field and precipitation downstream.

Rux

&&

.LONG TERM FORECAST (Days 4 through 7)...Thursday through Sunday...

The beginning of the forecast works well with deterministic
models through Day 5, but a change moving into ensemble models
finishes better through the end of the period. The longwave trough
over the Eastern Bering and Western Alaska, slips slowly
Southeastward into the Gulf of Alaska and the Eastern North
Pacific. High pressure holds over the Russian Far East and Far
Western Aleutians and Bering through the period. A moderately
strong shortwave rotates over the Eastern Bering and Western
Alaska to help reorient the trough towards the Southwest by
Sunday, with a number of weaker shortwaves to follow through the
pattern. A closed low forms over Southern Mainland, and drifts to
the East through the weekend.

Gustiest winds begin across the Bering and along the Alaska
Peninsula and Kodiak Island, with gale force gap winds likely
across the Alaska Peninsula and around Kodiak Island for Thursday
and Friday. Winds work their way across the Gulf with possible
gales developing over the Central Gulf late Friday into Saturday.
Widespread mixed precipitation spreads over the Bering through
Sunday for the Aleutians, with snow more likely over portions of
the Alaska Peninsula and Southwest Alaska. Southcentral areas
should see more snow than rain, while moderate rainfall will
continue over Southeast Alaska. In the Far West, an approaching
North Pacific low brings locally heavy precipitation and gusty
winds approaching gale force over the Western Aleutians through
Sunday.

Kutz

&&

.AVIATION...

PANC...VFR conditions and northerly winds generally 10 mph or less
will persist.

DAN

&&