673
FXAK68 PAFC 300046
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
446 PM AKDT Sun Sep 29 2024

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

East to southeast flow across the Gulf is bringing scattered
showers into the Eastern Kenai Peninsula and Prince William Sound
this evening. This activity is occurring within the remnants of a
weakening trough positioned over the western Gulf. High pressure
further inland is promoting mostly sunny skies for the rest of
Southcentral, which looks to remain the case through the latter
half of next week. With relatively benign conditions expected,
the primary challenge for Southcentral will be determining how
low overnight temperatures drop each night. The best chance for
any one location to see freezing or even subfreezing overnight
low temperatures will exist with areas that experience clear
skies during the overnight hours. Weak northerly flow through
Southcentral will favor just that, so we could see freezing
temperatures pretty much anywhere over inland portions of
Southcentral. A lesser chance for freezing overnight low
temperatures will exist further south for areas in closer
proximity to the Gulf coast where there will be some gusty winds.

Meanwhile, a deepening North Pacific low remains forecast to lift
into the southern Gulf by tomorrow afternoon. This low will be
accompanied by storm force winds and higher gusts offshore of the
coast and building seas of 25 to 35 feet in the offshore zones.
Models continue to suggest the low will "bomb out" with a minimum
low pressure in the upper 950s mb range tomorrow evening. Model
spread on central pressure has narrowed, but there is still some
spread. If the deepest solutions work out, Hurricane Force Winds
are not out of the question across the central Gulf offshore
waters. The low is then forecast to take a slow eastward track
into the eastern Gulf through Tuesday before finally exiting into
Southeast Alaska Tuesday night.

-BL

&&


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

A deep negatively-tilted longwave trough remains over the eastern
Bering into the eastern Aleutians this afternoon with a surface
low diving south across the Aleutians. A band of rain showers
continues to extend across Bristol Bay into the Kuskokwim Valley
near Aniak. Precipitation will lighten up through tonight as the
associated front weakens. The low will continue scattered showers
across the eastern Aleutians and the Alaska Peninsula through
Monday afternoon. Tonight, an intensifying low pressure system
entering the Gulf of Alaska will push the weakening front over
inland Southwest Alaska back westward with periods of showers
returning to Dillingham and the Ahklun Mountains by Monday
afternoon before dissipating.

Over the western Bering, a large but weak low will bring a pocket
of gale-force winds and steady rain as its front sweeps eastward
through the Aleutians. The low weakens below gale-force as it
pushes across the Alaska Peninsula and into the North Pacific
on Tuesday.

Heading into mid-week, there is increasing confidence for a
significantly stronger low to develop off Kamchatka and bring
more unsettled weather to the Bering Sea.

-ME

&&


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

The focus of the long-term forecast will be on a strong fall storm
that moves from the Kamchatka Peninsula towards the Eastern
Aleutians/Alaska Peninsula for the latter half of this week.
There is growing confidence that sustained winds will reach storm
force (55-73 mph), with gusts to hurricane force (> 73 mph)
possible. Potential impacts include high winds and coastal
flooding, though this will depend on the orientation of the winds
with regards to the shoreline. The worst conditions are expected
for Southwest Alaska, the Bering Sea, and Aleutian Islands from
Thursday through Friday, with generally improving conditions this
weekend as the low weakens.

Diving into the details...the first threat to watch for with this
storm system will be the low`s warm front, which will sweep
across the Pribilof Islands and into Southwest Alaska through
Thursday. The outlook could change, but recent model runs are
consistent in showing gale force (39-54 mph) south to
southeasterly winds as the front moves into Southwest Alaska. This
raises concerns that south-facing shorelines along Kuskokwim and
Bristol Bays could see a storm surge and potential high surf or
even coastal flooding. Winds look to be strongest along the
coastline, but interior parts of Southwest Alaska will likely
also see gusty winds.

From Thursday through Friday morning, cold air begins surging in
behind the low as it deepens to peak strength. The impacts from
this cold front will be much more sensitive to the position of the
low. Models seem to have shifted the track of this low further
west since yesterday, with the low expected to remain from about
Saint Matthew Island west. What this means is that the strongest,
storm force winds associated with this cold front are less likely
to reach the Kuskokwim Delta. Still, these winds could still pack
a punch, especially across the Western and Central Bering and
potentially as far east as the Pribilof Islands. While the current
low track looks to spare the Western and Central Aleutians of the
worst of the winds, expect sustained winds to gale force for these
areas.

While the worst of this storm will remain along the Bering Sea and
Southwest Alaska, Southcentral Alaska can still expect to see
some of its influence as the weakening warm front transits across
the Gulf through Friday. Expect sustained winds up to gale force,
with southeasterly, upslope flow favoring the highest rain amounts
along the coastline. In addition, the strength of the low could
lead to a tightening of surface pressure gradients and the
enhancement of winds through southeasterly terrain gaps like
Turnagain Arm, Knik Arm, and Copper River. However, the extent to
which the winds will be affected is somewhat uncertain as the low
center will remain quite distant from Southcentral.

Overall, this storm system will bear close watching. Please
monitor the forecast and stay tuned for updates.

-Chen

&&

.AVIATION...

PANC...VFR conditions will persist. There is a chance for gusty
southeast winds once again this afternoon through early evening,
with a weak Turnagain Arm jet sitting to the south. The approach
of a deep low from the Pacific toward the Gulf will quickly force
the Turnagain jet to bend southward this evening. So if gusty
winds do come in, they will be short-lived.

&&

$$