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FXAK68 PAFC 171345
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
545 AM AKDT Tue Sep 17 2024

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

A front, which is associated with a strong low in the Bering Sea,
is moving into Southcentral Alaska today. As has been the case
with the storms this past week, it is moving through the area
like a freight train leaving the break in between storm systems
measured in hours. While the worst of the weather with this low
will be in the Bering sea region, areas across Southcentral will
see more rain today with this front and then widespread rain shower
activity Wednesday as the cold core upper level low tracks across
the region.

Strong southeasterly winds will develop today into tonight for
Turnagain Arm, Knik River and the Copper River as the front moves
through the region. These winds will all subside when the low
itself tracks across the region. However, north and west winds
will increase through channeled terrain, especially along the Gulf
coast as the low traverses Southcentral. This will bring some
rather winds conditions from Kodiak to Whittier. While there will
be some offshore winds channeled down Valdez narrows and Arm, the
pattern is not conducive for significant winds there.

Thursday will see this low move to the east, but there remains
uncertainty as to whether Southcentral can start to see a little
bit of a break in between systems that lasts more than a few
hours to a day. While the next system looks to track well South of
Southcentral in the Gulf, the large upper level trough remains
over the mainland part of the state so that will make it difficult
for good clearing to take place.

&&


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

The forecast is continuing to be on track with an strong low
moving across the Pribilof Islands this morning into the eastern
Bering Sea toward Bristol Bay. Strong winds gusting 60 to 75 mph
are possible with significant wave heights to 30 feet in the
southeastern Bering Sea. A High Wind Warning has been issued for
the Pribilof Islands through 7PM tonight. As this energetic system
reaches Bristol Bay, an enhancement of winds along the Alaska
Peninsula and Bristol Bay could elevate surf and lead to beach
erosion along the coast. A High Surf Advisory continues for
Bristol Bay. Strong winds will also affect areas of the Eastern
Aleutians as well. A Special Weather Statement has been updated
for the Eastern Aleutians and the Alaska Peninsula. Please plan
accordingly and check for the latest forecast in your area.

-Rux

Previous Forecast Discussion:

The focus in the coming days will be a low currently north of
Adak, which will strengthen as it moves across the Bering Sea and
into the Alaska Peninsula for Tuesday night. Much of Southwest
Alaska, the Bering Sea, and the Aleutian Islands will see strong,
gusty winds from this low, with the potential for high surf and
coastal erosion. If you live in or will be traveling through these
areas in the coming days, please stay tuned to the forecast.
While there`s high confidence in the overall picture, finer
details such as maximum wind gusts continue to be refined. Here
are the products currently in effect:

* High Surf Advisory is in effect for Bristol Bay, primarily the
  from the Kvichak River mouth south to Port Heiden. Confidence is
  lower for areas west of the Kvichak River mouth, which includes
  Dillingham and Togiak.
* Special Weather Statement is in effect for the Pribilof Islands
  for strong winds and high seas.

Diving into the details...the low currently north of Adak will
strengthen through early tomorrow morning as it phases with a
robust upper low moving in from Kamchatka. Models came into
excellent agreement this morning, lending higher confidence to the
forecast. While there may still be changes to the forecast if the
low`s track changes, the overall strength of the system is
unlikely to change. As such, expect widespread gales across much
of the Bering Sea and Aleutian Islands, as well as the Southwest
Alaska coastline.

The strongest winds continue to be expected near the Pribilof
Islands tomorrow as cold air wraps back around the low. There is a
chance that gusts could come in at hurricane force, which is 75
mph or greater. However, the current forecast has gusts remaining
just below this threshold as confidence is low that the strongest
winds aloft will mix down to the surface. Regardless, it will be
a very windy day for Pribilof Islands and surrounding waters.

Strong winds are also expected across the Eastern Aleutians,
Alaska Peninsula, and Bristol Bay. Winds will be southwesterly
for much of Tuesday, generally parallel to the shoreline. However,
as the low moves inland near Naknek/King Salmon early Wednesday
morning, flow will become more westerly. This will focus wind and
waves directly onshore, leading to the potential for high surf and
coastal erosion. As such, a High Surf Advisory is in effect for
Bristol Bay.

While high surf/coastal flood products are not in effect
elsewhere, there still may be minor impacts. For the south-facing
shore of Kuskokwim Delta (ex: Kipnuk to Kongiganak), southeasterly
onshore flow along the front on Tuesday morning could bring a
brief period of higher water levels. However, this is expected to
be short-lived and not as impactful as this past weekend`s storm.
Similarly, the south-facing shore of Bristol Bay (from the Kvichak
River mouth to Cape Newenham) could also see higher water levels
from surge as there will be decently long duration of onshore
winds. However, these winds will be weaker than those impacting
the portion of Bristol Bay under the High Surf Advisory. Finally,
the Bering side of the Alaska Peninsula (especially Nelson Lagoon)
will also get their turn at strong winds from Tuesday evening
through early Wednesday morning, though the winds will not be
directly perpendicular to the shoreline. Overall, confidence
remains low when it comes to the potential for high surf and
coastal flooding due to lack of observations and modeling methods
that are still relatively new.

Looking ahead, northerly flow behind the departing low will usher
in cooler air, with much of Southwest Alaska seeing temperatures
in the 30s from Wednesday night through Thursday morning. This, in
combination with weak upper level shortwaves moving in behind the
low, could result in a fresh dusting of snow along area mountains
and even on lower foothills.

-Chen

&&


.LONG TERM FORECAST (Days 4 through 7: Friday through
Monday)...

There is little agreement amongst operational models by the end
of the work week on Friday. Even the ensemble means largely differ
from each other during the same time period. From a pattern
perspective, the general consensus is for a broad trough or upper
low over the Western Aleutians and western Bering to gradually
slide eastward through the beginning of next week on Monday. The
operational GFS, in particular, is more aggressive with yet
another strong low overspreading the Western and Central
Aleutians. Ensembles eventually have the low positioned over the
Gulf of Alaska by the end of the long term forecast.

As far as potential impacts, the track of the trough should keep
the threat of shortwaves over the Aleutians on Friday and
Saturday. As the general trough continues eastward, the track of
disturbances moves south of the AKPEN and eventually well south of
the Gulf coast. Therefore, moderate confidence exists in somewhat
of a quieter pattern setting in for the long term for Southwest
and Southcentral Alaska with any upper-level jet support remaining
south of mainland Alaska.

What this will do however is present the opportunity for colder
air to drop southward into both Southwest and Southcentral Alaska.
Thus, cooler temperatures are likely along with lower
precipitation chances.


-BL

&&


.AVIATION...

PANC...VFR conditions persist through Tuesday morning, then MVFR
ceilings and light rain are possible through Wednesday.
Southeasterly Turnagain Arm winds increase by Tuesday afternoon
with gusts over the terminal up to 25 kts possible, decreasing
Tuesday night.

&&


$$