Gale Warning 812, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
553 AM AKST Fri Dec 15 2023

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

A transient upper-level ridge is quickly moving east across
Southcentral this morning as a frontal system attached to a
surface low near Nunivak Island moves over Southwest Alaska and
toward Cook Inlet. Light snow is already visible on radar, with
light snow falling from Kodiak to Seldovia as of 4 am. Snow
showers are also moving north from the northern Gulf toward
Cordova.

The snow over the Barren Islands will become more widespread
across the eastern half of Southcentral as southeasterly gap winds
develop through Turnagain Arm. Areas of blowing snow are possible
by late morning from Portage to Indian and across the Anchorage
Hillside before a secondary surface low develops south of the
Kenai Peninsula and both the pressure gradient shifts and the
winds turn westerly. Snowfall amounts will generally be light, on
the order of 2 to 4 inches. However, snowfall amounts may push 6
inches or more for the Anchorage Hillside as well as other
locations favored by a southwesterly upslope flow. Snowfall rates
may also increase by mid to late afternoon across the Anchorage
Bowl and Mat-Su Valleys as the upper-level shortwave gains
strength and a temperature gradient at 850 mb tightens with cold
air advecting in from the west.

Snow will continue to move west through the afternoon as the low
over the northern Gulf becomes the primary feature and quickly
moves toward Kayak Island overnight. Snow over Prince William
Sound and the Copper River Basin will wind down overnight. Skies
should clear behind this feature; however, lingering low stratus
is possible across Cook Inlet through Saturday morning.

Attention then turns back to the west as a storm force low sweeps
a front from Kodiak Saturday morning to the Southcentral coast by
Sunday morning. Strong wind gusts are likely both along the coast
and through gaps as the pressure gradients tightens. Heavy
precipitation is also likely along the coast with ample moisture
advecting over the Gulf with east-southeast winds. The challenge
will be whether places along the coast see enough of a warm up
with the winds to change snow over to rain by Sunday morning.
Upwards of a foot of snow is possible from Thompson Pass to
Turnagain Pass if enough cold air remains in place. Locations in
the lee of the mountains will likely see little precipitation due
to downsloping. Southerly winds and a brief warm up is likely from
Kenai to Palmer as the front lifts north by midday Sunday.
However, this system will be quickly occluded with colder air
wrapping back in. So any brief warm up with southerly winds should
come to an end as winds diminish and colder air returns by Sunday
evening.

&&

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

On satellite imagery there is a front over the eastern Bering and
Southwest Alaska. Also on satellite imagery, there is a fetch of
modified tropical air pushing into Bristol Bay the extends into
the west Pacific Basin. This system is bringing light snow
showers to portions of Southwest Alaska. This feature will advance
towards Southcentral Alaska. Expect a break in precipitation then
a second low will be in the vicinity of Cold Bay Saturday
morning.A tight pressure gradient will form during the evolution
of this low as it moves from the North Pacific, jumps the chain
and into the Bering. Expect more unsettled weather for the central
and eastern Aleutians and Southwest Alaska. Sunday, a third front
will push over Attu Island and will reach the central Aleutians
on Monday.

&&

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

A broad upper level longwave trough extends across the Bering
into Western Alaska through the period. A strong shortwave extends
through the Gulf of Alaska and continues its track into the
Canadian Provinces through Thursday. The longwave trough will
spread into the Western Interior. Subsequent shortwaves sliding
along the base of the longwave trough provides the track to
develop a series of surface low centers to move over the Aleutians
and Alaska Peninsula into Western Alaska and the Gulf.
Occasionally heavy showery precipitation moves over the Aleutians
and Pribilofs. Widespread gusty winds with areas of Easterly gale
force winds and possible storm force gusts over the Bering, and
Westerly gales along and over the Aleutians through Wednesday,
diminishing Thursday.

Low centers developing along the front South of the Alaska
Peninsula Tuesday continue their Eastward trek into the Gulf of
Alaska Wednesday and Thursday. Some gusty winds spread over the
Gulf, but the main threat will be additional, locally heavy
precipitation accompanying the warmer air intrusion ahead of the
low over the Southcentral portions of the state through Thursday.
Kodiak Island will have mixed rain and snow. Southcentral coastal
areas start with snow, but change to rain, with areas of snow
further inland. Significant accumulations from Prince William
Sound and East are expected.

Kutz

&&

.AVIATION...

PANC...Low stratus over Cook Inlet contributed to LIFR conditions
during the early morning hours with ceilings down to 200 feet.
Conditions at PAFC currently are hovering on the edge of IFR and
LIFR with ceilings just below 500 feet. IFR conditions are
forecast to become more prevalent through this afternoon with
light snow developing between 16z and 18z. Snow should linger
through roughly the 06z time frame. As snow finally tapers off
ceilings are expected to lower yet again with potential LIFR
conditions resuming tonight.

&&