Gale Warning 546, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
438 AM AKDT Thu Sep 28 2023

.ANALYSIS AND UPPER LEVELS...

Mostly zonal flow exists in the primary jet core to the south of
the Aleutian Chain. Over the Bering, a shortwave trough and an
occluded low is moving slowly east. It's front has reached the
southwest coast, bringing southeasterly winds and rain to the
Kuskokwim Delta. Well south of the Western Aleutians, the
baroclinic leaf of a developing system expected to impact the
southern Mainland this weekend can be seen on Satellite. A slight
shortwave ridge and zonal flow over the Aleutian Range is bringing
mostly clear skies to the Kenai Peninsula, while a shortwave
trough over the Copper Basin has lead to cloudy conditions, light
rain, and even some snow near Tahneta Pass.

&&

.MODEL DISCUSSION...

Models continue to evolve in their phasing of an arctic shortwave
with the stronger north Pacific low as it reaches the Gulf on
Sunday. Current progs show less distinct phasing of the two
shortwaves, and more of an invigoration of the storm system on
Monday as the arctic airmass and trough reintroduces lee-side
troughing and eventually deformation over Southcentral. There are
some difference in how progressive this system will be, with the
GFS stalling the upper low over the northern Gulf while the
ECMWF/GEMNH solutions progress the wave into Southeast.

&&

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

&&

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

Another beautiful Autumn day on tap for Southcentral with partly
cloudy skies, light winds, and seasonable temperatures. Any
precipitation today will be limited to scattered showers in
Prince William Sound and the Copper River Basin. A transition to a
more cloudy and wet pattern begins tonight as a deep low moves
north and east out of the north Pacific through Saturday. A
frontal boundary associated with the low will lift north into the
central Gulf tonight and progress towards the northern Gulf and
Gulf coast on Saturday. Ahead of the low expect increasing chances
for showers for the Prince William Sound and Southcentral coast
tonight and into early Saturday. More widespread rain will lift
north across the western Gulf, spreading across Kodiak Island and
southern Kenai Peninsula Friday night and gradually spreading
northward through Saturday. Much cooler temperatures are expected
to move into the area beginning Sunday night and Monday.

&&

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

The forecast remains on track for Southwest Alaska and the
Aleutian Chain. Rain begins to spread across the southwestern
Mainland early this morning, persisting into the overnight hours,
as a weak front pushes onshore. Conditions will become dry again
on Friday as the front dissipates and the associated low fizzles
out. The next system is tracking towards the Aleutians out of the
North Pacific over the next few days, with the associated front
expecting to move over the Chain Friday morning. Anticipate
widespread rainfall and gale force winds along the Eastern
Aleutians and southern Alaska Peninsula Friday and Friday night.
Rain then pushes into Bristol Bay Friday night before the front
begins to decay. Colder air aloft filters across the Bering Sea
behind the low, allowing for the possibility of enhanced gap winds
south of the Eastern Aleutians and southern AKPen Saturday evening
into Sunday morning.

&&

.LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...

Forecast models bring a 990 mb low into the Gulf coast Sunday
morning. Widespread showers, with the potential for heavy rain
along the Gulf coast, will be in the process overspreading
Southcentral and Southeast Alaska. The center of the low is
forecast to hang up over Prince William Sound into Monday before
slinking eastward into Canada Monday night. Upstream ridging over
the western Bering will aid cooler upper level temperatures
dropping southward across interior Alaska on the backside of the
upper low over the Gulf. 850 mb temperatures as cold as -10
degrees begin to filter across Southwest and Southcentral Sunday
night into Monday. This should be the coldest air mass into our
domain so far this Fall, but it might also arrive with little to
no precipitation. Forecast models are not in good agreement with
the evolution of an arctic trough into Southwest over the weekend,
and there is the possibility of snow levels remaining elevated.
Of greater confidence is the likelihood of northerly gap winds
through the Alaska Peninsula and into the Barren Islands. Denser
cold air may enhance outflow winds through Seward and Valdez as
well, but timing and intensity of said winds are less certain. The
next forecast challenge entails the arrival of a potentially
strong Western Aleutian low by the middle of next week. Here
again, however, models are not in good agreement with the low's
development. A broad front will likely precede the low, regardless
of intensity and placement, which will introduce enhanced
southerly winds into the Central Aleutians along with heavier
showers.

&&

SYNOPSIS AND MODEL DISCUSSION...CJ
SOUTHCENTRAL ALASKA...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
LONG TERM...BL