Gale Warning 796, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
453 PM AKST Fri Dec 8 2023

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

The main upper trough axis that swept through Southcentral from
the southwest early this morning is now swinging up towards the
northern Alaska Range. This has given way to a showery pattern
across mainly the Gulf, with a much colder air mass and southwest
flow aloft. Most of the snow showers are staying out over the Gulf
for the time being, but they will likely soon begin to work back
onshore later this evening into tonight.

Overall, the forecast confidence for Saturday morning onwards has
unfortunately not improved much compared to 12 hours ago. Models
are still struggling to lock in on the trajectory and progression
of a weak shortwave trough moving into the Kenai Peninsula and
Prince William Sound region from the southwest on Saturday while a
small, weak low spins up just south of the Kenai Peninsula and
shifts in the same direction through Saturday evening. This setup
is not terribly unlike what we just saw come through in the past
24 hours, but will not feature much on the way of cold advection
with the colder air mass already in place out ahead of this next
feature. Scenarios for snowfall timing and amounts still vary
considerably for Saturday, but the overall thinking is still for
light snow to develop over the southern Kenai Peninsula late
tomorrow morning, then spread northeast up into Kenai Peninsula
later in the day, and finally move out towards Valdez and Cordova
during the afternoon and evening as a deeper, west to east
oriented upper trough lifts north into the southern Mainland.
Given the continued spread in even higher resolution guidance,
will still with a general 0.5 to 2" for the Mat Valley, Anchorage
and western Kenai Peninsula corridor, with higher amounts up to
6" out closer to Seward and Whittier through Saturday night.

Attention from there quickly shifts to what could become a fairly
high impact system across at least parts of Southcentral starting
on Sunday. On Sunday morning, a low pressure over the North
Pacific will move up near Kodiak Island by Sunday morning as an
upper ridge rapidly builds out ahead of it into the Gulf.
Widespread precipitation will spread from Kodiak Island up into
the Gulf Coast as a warm front lifts north throughout the day,
affecting mainly the coastal mountains as developing southeast
low level flow carrying higher moisture north and west upslopes
into higher terrain. Solutions for the track of this low have
largely trended west, with it looking increasingly likely the
surface low will track north somewhere along the western Alaska
Range, potentially going right up the Cook Inlet through Monday
morning as the supporting upper trough phases with the upper
level low drifting over Bristol Bay. This more west track compared
to what we've seen from earlier projections would favor much more
cross-barrier flow setting up across the Kenai and Chugach range,
limiting snowfall potential for the Mat Valley and Anchorage Bowl
until the occluded front lifts through sometime on Monday. Strong
gap winds through the Turnagain Arm, Thompson Pass and Matanuska
Valley will also be a concern, potentially leading to issues with
blowing snow between Sunday and Monday in these areas as well.

There is still a lot of room for details with this storm system to
change, so please continue to monitor the forecast as we further
dial in details over the next couple days.

-AS

&&

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

An upper trough persists over the Kuskokwim Delta through
Saturday with one or more shortwaves to rotate through the trough
and just offshore of the Kuskokwim coast. High pressure remains
over the western Bering, while an eastward moving shortwave
trough tracks south of the Aleutians before eventually wrapping
northward into the Greater Bristol Bay area on Sunday. The
Kuskokwim Delta trough will sag slightly southward with the
passage of each shortwave today and tomorrow. A pattern change
then begins to develop by Sunday as the trough phases with the
wave lifting into Bristol Bay, forming a much more amplified
trough over the AKPEN and Western Alaska Range over the latter
half of Sunday.

For tonight, calmer conditions continue for the rest of Southwest
Alaska. Scattered light snow will remain possible tonight and
tomorrow while the presence of the upper trough lingers over
Southwest Alaska. There is some uncertainty in regard to potential
heavier snow amounts over the Greater Bristol Bay region on Sunday.
The NAM seems to be the most aggressive model with Iliamna
accumulating 4 to 6 inches of snow through the weekend. Finally,
the Kuskokwim Delta should experience a notable temperature drop
over the next 36 hours. Current temperatures in the teens steadily
decrease to near zero by Sunday morning as northerly flow opens
up over the Kuskokwim Delta.

Elsewhere northerly flow and weak high pressure will persist in
the Bering Sea. The only significant change will occur over the
Western and Central Aleutians as a subfreezing air mass spills
well south of the Aleutians through Monday.

&&

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

The weather pattern continues across the region through Friday.
Ridging over the Western Bering and Canadian Provinces brackets
the reorienting longwave trough over Mainland Alaska. A number of
energetic shortwaves continuing their trek along the Western edge
of the trough bring uncertainty to the composite blend of models
over the initial periods. The closed low center in the mid-trough
weakens through the end of the forecast period, as it loops around
the Southcentral coast. With colder air pouring in with the
trough, most precipitation will be snow showers over Western
Alaska and along most of the Alaska Peninsula and Aleutians. Along
with the snow, gusty winds increase to gale force over the
Eastern Bering, Alaska Peninsula and Eastern Aleutians,
diminishing late Thursday. Further West, a well developed
Kamchatka low extends a front over the Western Bering and
Aleutians, with mixed rain and snow as well as gales along the
front through Friday.

Over the Gulf of Alaska, transient lows and fronts from the North
Pacific spool up a widespread multi-day precipitation event from
the Alaska Peninsula to the Canadian Border. Coastal areas begin
with locally heavy rainfall changing to snow further inland as the
area spreads to the Alaska Range through the end of the week.
Gusty winds offshore increase to gale force for Thursday and
Friday, with a gale barrier jet along the North Gulf Coast late
Thursday, diminishing Friday.

Kutz

&&

.AVIATION...

PANC...VFR conditions are expected through at least Saturday
morning before the next system starts to approach. However, with
mostly clear skies allowing for modest radiational cooling
overnight, there is the potential for fog to develop in the
vicinity of, or move into, the terminal after 12Z. If fog does
develop, expect ceilings to drop to below 500ft and visibility to
under 1SM.

&&