Storm Warning 123, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
435 PM AKDT Tue Oct 1 2024

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

Discussion:

Southcentral finds itself between two strong upper-level troughs,
and with weak ridging building at the surface, conditions across
the region have cleared. Weak continued offshore flow and a push
of dry air from the north has allowed for dewpoints in the teens
and 20s to push into the Copper River Basin and down into the Mat-
Su Valley, though not as far south at the Anchorage Bowl.
Elsewhere, winds and/or more cloud cover will help to prevent
temperatures from falling to low. Cold temperatures are expected
across the larger area of Southcentral Wednesday morning, with
exceptions expected to include locations directly along the Gulf
coast such as Cordova and Seward. For areas in the Copper Basin
where skies have remained clear and winds have calmed,
temperatures will fall to below freezing by Wednesday morning.

This lull and period of clearer weather appears to expire by late
Wednesday afternoon and evening, filling in skies over much of
Southcentral and bringing rain to the coast as a new low pressure
system fills into the northern Gulf of Alaska. As the low lifts,
it is expected to weaken, bringing showery conditions to the
coastal zones through Thursday. This system is expected to be
supported later by a following stronger system in the Bering Sea
that will push a relatively stronger front into the Gulf of Alaska
by Friday. This pattern may maintain the wet pattern across the
Gulf Coast into the weekend, with interior Southcentral appearing
mostly dry, but more cloudy.

-CL

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING SEA/ALEUTIANS...

* HIGH WIND WATCH in effect for the Western, Central and Eastern
  Aleutians Thursday into Friday

Weak onshore flow coincident with a weak upper level shortwave
continues areas of low stratus and scattered showers across the
Kuskokwim Delta this afternoon. While conditions are expected to
clear out tonight, redevelopment of fog is possible across the
Kuskokwim Delta and possibly further south along the Bristol Bay
coast as well.

Further west over the Bering, a longwave trough axis will dive
south and get stretched out over Southwest Alaska on Wednesday. At
the surface, a broad but weak low will push its front eastward
through the Bering, weakening as it reaches the Southwest coast
Wednesday evening.

A robust hurricane-force low off the coast of Kamchatka enters
the western Bering Sea for Thursday. Its front will move over the
Pribilofs and central/eastern Aleutians Thursday morning bringing
southeasterly gales and rain throughout the day Thursday. There is
still spread among the ensemble model guidance on the strength
and exact track of the low as it moves eastward. If the low moves
farther north, winds may be less intense for the Aleutians as the
strongest hurricane force winds associated with modest cold air
advection on its backside stays over the water, while a southerly
track could result in even stronger winds.

Regardless, very strong winds and high seas (nearing 30 to 40
feet in the southern Bering) can be expected as the low quickly
deepens to near/just below 960 mb. A High Wind Watch is in effect
for the entire Aleutian chain. For the western Aleutians, gusts up
to 85 mph are possible late Wednesday night through Thursday
afternoon, and Thursday afternoon through late Thursday night for
the central Aleutians. For the eastern Aleutians, gusts up to 75
mph are possible Thursday afternoon through Friday afternoon. For
the Pribilof Islands, winds will turn westerly behind the low as
it moves east Thursday night into Friday. Gusts to of 55 to 65 mph
are expected Friday morning through Friday evening before slowly
diminishing. The duration and magnitude of the westerly winds will
be highly dependent on storm track. A more southerly track will
allow for a lull in the strongest winds late Thursday through
early Friday morning before the winds shift to the west. A more
northerly storm track will allow for a quick wind shift from
southeast to west and a longer duration of stronger winds. If the
northerly track takes shape, wind gusts could be stronger, closer
to 60 to 70 mph. However, confidence in this storm track and the
higher wind gusts is low.

The low's initial front with south/southeasterly gales pushes
into southwest Alaska Thursday evening and stalls out and weakens,
bringing a period of elevated winds and light to moderate rain
through Friday morning. Given the fronts orientation and fetch,
coastal flooding concerns are none to low at this time.

Eovino

&&

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

The focus in the long-term continues to be a strong storm system
moving from the southeastern Bering late Friday across the AKPen
and into the western Gulf by Sunday morning.

There is high confidence that storm force (55-73 mph) wind gusts
will persist across the eastern half of the Aleutian Chain, as
well as parts of the AKPen, late Friday as the storm system begins
to weaken and drift southeast toward Bristol Bay. As the low
moves south of Kodiak Island Sunday, gusty northwesterly winds
will continue across the eastern Aleutians and AKPen, albeit
slowly trending downward, with widespread gale-force winds and
storm-force gusts Saturday weakening to gale-force gusts by
Sunday.

Farther east, the occluded front associated with the low will
will weaken and become more east-west oriented over Southwest
Alaska by Saturday morning. The strong southeasterly winds
expected Friday will diminish as the front shifts, with winds
becoming more northeasterly on Saturday then northwesterly by
late Sunday. The precipitation along the front will also diminish
from north to south through early Sunday as the northerly wind
flow ushers in cooler and drier air.

The aforementioned occluded front enters the western Gulf late
Friday with rain and strong easterly gales across Kodiak Island.
The front then lifts to the north Gulf coast Saturday morning as
the parent low drifts south across the AKPen. A strong easterly
barrier jet is expected to develop along the coast for Saturday.
The east-southeasterly flow aloft out ahead of the front will also
drive copious amounts of moisture into the coast and over the
coastal mountains. Precipitation will continue into Sunday as
trailing upper-level waves lift south to north across the Gulf in
the wake of the initial front. The track and strength of these
features will dictate where the heaviest precipitation falls.
However, an increase in instability with these waves will bring
about a more convective and showery nature to the precipitation,
potentially leading to waves of moderate to heavy precipitation
along the coast into early next week.

-TM

&&

.AVIATION...

PANC...VFR conditions and light southerly winds are expected
through the forecast period.

&&