Gale Warning 561, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
523 AM AKDT Wed Oct 11 2023

.ANALYSIS AND UPPER LEVELS...

An upper trough, which has been nearly stationary over the Seward
Peninsula that last several days, continues to harbor a much
cooler air mass over the state of Alaska. To find above freezing
temperatures one most go down to the Alaska Peninsula or stay
close to the coastal waters of the Gulf or Cook Inlet in
Southcentral. A surface trough is lingering over the northern
Gulf, with widely scattered showers clipping Prince William Sound.
A shortwave trough is moving across Cook Inlet, which may enhance
some precipitation over the Anchorage Hillside and down along the
Seward Highway into the western portion of Prince William Sound.
The bigger weather feature this morning is the arrival of a storm
force low into the Western Aleutians. Gusts to hurricane force are
likely with this low as it continues to deepen while
overspreading the Central Aleutians through tonight. The southern
Bering into Southwest Alaska remains largely dry this morning
under the presence of weak high pressure ridging downstream of the
approaching Western Aleutian low. With high pressure over
Southwest and an area of low pressure over the northern Gulf,
enhanced northwesterly gap winds are spilling through the upper
Alaska Peninsula at small craft speeds, and near gale speeds out
of the Kamishak gap.

&&

.MODEL DISCUSSION...

Models remain in surprisingly good agreement this morning.
Digging into the finer details a surface trough over the northern
Gulf will see multiple smaller disturbances lift across the trough
and Southcentral over the next couple of days. Models are in less
agreement with the placement of precipitation from Prince William
Sound into the Susitna Valley as each new disturbance renews
precipitation over Southcentral. Periods of rain and snow are
forecast to grace the Anchorage Bowl and further north up into the
Valley. However, distinguishing precipitation type, timing,
amounts, and frequency of precipitation will be a bigger
challenge.

&&

.AVIATION...

PANC...MVFR conditions are forecast today into tonight with
ceilings occasionally climbing above 5000 ft. A shortwave tracks
up Cook Inlet through this evening, which may promote a few
flurries. The next best chance for precipitation develops after
dark as a surface trough pivots from Prince William Sound into the
Anchorage Bowl.

&&

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

Very little change to the overall forecast as an upper low continues
to rotate over the Seward Peninsula with several shortwave troughs
rounding the base and eastern side of the low. This has allowed some
colder air to slowly filter over the Alaska Range and into portions
of Southcentral. The shortwave trough now swinging north towards
central Alaska may produce some flurries and/or light snow for
northern portions of the Copper Basin and along the southern flank
of the Alaska Range this morning. The next shortwave (currently
rounding the base) will swing into the AKPen and southern Kodiak
Island today before slowing as the southern end phases with a low
moving into the Gulf. The parent low will finally start to push off
to the east as longwave ridge steepens ahead of the strong system
that will impact portions of the western and Aleutian islands later
tonight.

In addition to the aforementioned low over Seward Peninsula...a weak
area of low pressure near Middleton Island is still producing some
scattered rain showers over Prince William Sound and rain/snow
showers along the southern side of the Chugach Mountains. A weak
area of convergence has developed along the Cook Inlet and eastern
Kenai Peninsula, extending up into the Susitna Valley. With
temperatures having dropped generally into the low to mid 30s and
lift once again increasing over the region, an area of light snow is
expected to develop near this area of convergence...primarily from
the northern Kenai Mountains northward into the Susitna Valley. Hi-
res models are also showing this area of light snow beginning this
morning with on-again-off-again chances of light snow or flurries through
the day. Light snow will start to spread across the rest of the
Kenai Peninsula and Chugach Mountains on Thursday as the Gulf low
moves north towards the Southcentral coast. However, warmer air
will accompany this system and snow will start to transition to
rain for the lower elevations late Thursday into Friday.

&&

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

The storm-force low moves into the Bering Sea this afternoon.
Currently over the Western Aleutians, it will progress eastward
through tomorrow. Storm force winds with hurricane force gusts are
expected over the Western and Central Aleutians today into
tomorrow, and high end gales with storm force gusts are expected
over the Eastern Aleutians and Pribilof Islands. The High Wind
Warnings and Special Weather Statement remain in effect for the
aforementioned areas. The low eventually places itself west of the
Pribilof Islands and sits there and weakens through the end of
the week.

Southwest Alaska, which has experienced largely mild conditions
the past couple of days, will continue to see similar conditions
today.

&&

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

An unsettled and soggy extended forecast on tap for much of the AOR
as multiple low pressure systems work along the Aleutians and into
the Gulf of Alaska through the weekend/early next week.

Out West, the powerful Bering Sea/Aleutian system that is expected
to bring Storm to Hurricane force winds to the western and central
Aleutians should weaken/open by Friday night, with localized gale
force winds lingering over the central Aleutians as the system slows
and stalls through Saturday morning. As the system stalls and
loses steam fighting an upper lvl ridge, expecting a transfer of
energy to a seperate developing low pressure system within the N
Pacific. This developing low brings about sporadic near-Gale
force winds along the southern periphery of the east/central
Aleutians by Sunday through Tuesday.

For Southcentral, rain chances increase moving into the late weekend
as multiple low pressure systems push into the Gulf of Alaska. At
this time, not anticipating impactful rain/snowfall amounts through
the weekend, however, can't rule out light precip across the
Anchorage/MatSu saturday night into Sunday as a low pressure system
pushes into Prince William Sound. Otherwise, much of the extended
forecast plays into the evolution of TS Bolaven, currently located N
of Guam. Beyond the weekend timeframe, confidence is increasing that
the remnants of this storm will move into the Gulf of Alaska,
bringing with it potential for heavy rain and increased winds.

NM

&&

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

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
140 PM AKDT Wed Oct 11 2023

AKZ195-121400-
Pribilof Islands-
Including the city of Saint Paul
140 PM AKDT Wed Oct 11 2023

...STRONG WINDS FOR THE PRIBILOF ISLANDS THURSDAY MORNING THROUGH
FRIDAY MORNING...

A weather front attached to a powerful Bering low will advance
east to the Pribilof Islands by Thursday. Southeasterly winds will
rapidly increase late Wednesday night and continue through
Thursday before slowly diminishing early Friday morning. For Saint
George Island, sustained winds of 35 to 50 mph with gusts up to
70 mph are likely. For Saint Paul Island, sustained winds of 30 to
45 mph with gusts to 65 mph are likely. The strongest winds are
expected between 8 AM and 10 PM Thursday.

AKZ185-121400-
Eastern Aleutians-
Including the cities of Unalaska and Nikolski
140 PM AKDT Wed Oct 11 2023

...STRONG WINDS FOR THE EASTERN ALEUTIANS WEDNESDAY NIGHT THROUGH
THURSDAY AFTERNOON...

A weather front attached to a powerful Bering low will advance
east to the eastern Aleutians by late Wednesday night.
Southeasterly winds will rapidly increase Wednesday evening and
continue through early Thursday afternoon before slowly
diminishing Thursday evening. For Nikolski, sustained winds of 35
to 50 mph with gusts up to 70 mph are likely. For Unalaska and
Akutan, sustained winds of 30 to 45 mph with gusts to 65 mph are
likely. The strongest winds are expected between 10 PM Wednesday
and 2 PM Thursday.