868
FXAK68 PAFC 250101
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
501 PM AKDT Tue Sep 24 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA
(Days 1 through 3: This afternoon through Friday evening)...

Unsettled weather will continue to rule the roost over much of
Southcentral Alaska through Thursday. The main culprit of the
unsettled and rainy regime is a broad upper-level trough
stretching from the Arctic, southward across western Alaska, and
eventually into the central Gulf of Alaska. This trough is
anchored by a vertically stacked low in the Gulf. Numerous upper-
level waves will continue to rotate about this low and over
Southcentral. Wettest areas will continue to be along the north
Gulf Coast, Prince William Sound, and Eastern Kenai Peninsula.
Inland locations will see showery conditions more-so than steady
rain. Brief upticks in rain intensity are possible in heavier
showers. The best time for more wide-spread showers inland will be
this evening into tonight when an inverted trough over Prince
William Sound rotates westward and over the area. In addition to
the precipitation associated with this inverted trough, it will
also bring a push of higher easterly winds tonight across the
north Gulf Coast, including Cordova, into Prince William Sound,
and possibly into Passage Canal/Whittier.

The inverted trough will continue its journey westward for
Wednesday and bring The Susitna Valley widespread showers mostly
from Talkeetna and southward. Rainfall amounts continue to be a
challenge to hone in on due to the fact it is difficult to
determine where exactly the heaviest showers set up. In general,
expectations are for between a tenth to a third of an inch of
precipitation from the Susitna Valley south to the communities
along Cook Inlet, and into the Copper River Basin from now through
late Wednesday evening. The low in the Gulf will continue to
weaken on Thursday, but as previously mentioned, cyclonic flow and
weak upper waves moving across the area help to keep showery
activity going; albeit with less coverage compared to Wednesday. A
Bering Sea low looks to cross the southern Alaska Peninsula and
enter the North Pacific later on Friday with its front clipping
southern Kodiak Island by then. This will be the next system to
follow for the weekend as the front lifts northward through Gulf
and brings more in the way of widespread steady rains for coastal
Southcentral.

&&


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

The upper-level longwave trough remains stretched north to south
along the western portion of Mainland Alaska, with a weak ridge of
higher pressure built in the western Bering. Elevated winds
through the gaps and passes south of the Eastern Aleutians and
southern Alaska Peninsula this afternoon will taper off tonight. A
similarly gusty but not particularly strong wind pattern is
expected by Wednesday afternoon, again tapering off by Thursday
morning. Morning low temperatures across Southwest Alaska will
continue in the low to mid 30`s, and low 40`s along the Alaska
Peninsula and Eastern Aleutians. Fairly clear skies over coastal
Bristol Bay currently expected to continue into late Thursday
night.

Through today, upper-level shortwaves rotating around the base of
the longwave trough will curve across Southcentral Alaska and back
towards Southwest Alaska, producing a deformation band along the
Western Alaska Range and Middle Kuskokwim Valley. The models
continue to trend the progression of the deformation band slower,
with the arrival time now expected by Wednesday morning. Still,
this band is expected to bring prolonged light precipitation
persisting through at least Wednesday with the potential to linger
showers in the area as late as Thursday afternoon as the band
slowly breaks down. As temperatures drop overnight, precipitation
type will likely similarly change each overnight period to snow,
returning to a mix of precipitation in the afternoons.

The next system to enter the fray will be a vertically stacked
upper-low entering the northwestern Bering Sea by Wednesday night
into Thursday morning. A front along the eastern leading edge of
the front will spread across the Bering ahead of the main low,
reaching the Pribilofs by Thursday morning. While the front
appears fairly transient, the upper low appears to stick into the
central Bering continuing the active pattern through the weekend
for the Bering and Southwest coastline. The Central Aleutians may
expect to see showers likely beginning as early as Thursday
evening, persisting into the early-to-mid weekend.

-CL

&&


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

Global models are in good agreement with a broad longwave trough
continuing to persist over mainland Alaska through the extended
forecast period. Quick moving shortwaves will impulse along the
trough bringing continued moderate to heavy precipitation along
the Alaskan-Kenai Peninsulas, Gulf Coast and coastal mountain
ranges. Ridging high pressure over the eastern half of the State
will bring moderate northeasterly to easterly winds along the
central Aleutians.

The preferred GFS and ECMWF models align with a strong North
Pacific Low moving up into the Eastern Gulf of Alaska by Late
Monday and dissipating as it moves ashore in the northern
Panhandle on Tuesday. The Canadian model has the low persisting
past Tuesday but lingering over Prince William Sound beyond the
forecast period. With the models coming more into agreement with
each run confidence is improving with the systems track, intensity
and timing. Continue to monitor for future updates on this system
for early next week.

&&

.AVIATION...

PANC...VFR conditions and light northerly winds will prevail
through the TAF period. It is possible for ceilings to drop
periodically to MVFR Tuesday evening through Wednesday morning due
to a mesoscale surface low moving in from Prince William Sound.
This wave should bring precipitation that is showery in nature and
low decks are mostly expected to remain scattered. By midday
Wednesday a drying trend should begin, bringing higher ceilings
and VFR conditions.


&&


$$