885
FXAK68 PAFC 180111
AFDAFC

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

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

A front, which is associated with a strong low currently in the
eastern Bering Sea, continues to move into Southcentral Alaska
this afternoon and evening. While the worst of the weather with
this low continues to be in the Bering sea region and Southwest
Alaska, areas across Southcentral will see more rain tonight with
this front and then widespread rain shower activity Wednesday as
the cold core upper level low tracks across the region.

Strong southeasterly winds continue  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 windy 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 majority of guidance continues to depict
the next system from the North Pacific tracking well South of
Southcentral in the Gulf, the Canadian guidance depicts a stronger
low tracking to the Alaska Peninsula with the front lifting north
across Kodiak Island mid-day Friday and to the North Gulf Coast by
Friday afternoon and evening. This system will be the next one to
watch and see if trends continue to argue for the more southern
track. Regardless of that, 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: This afternoon through Friday afternoon)...

The forecast remains on track, with only minor adjustments to the
low track and strength. The biggest thing to note is the increase
in wind speeds, especially for the Alaska Peninsula and Bristol
Bay, from this evening into the overnight hours. The High Surf
Advisory has been updated to reflect these higher winds, with
gusts of 60-70 mph now expected. Otherwise, a High Wind Warning
remains in effect for the Pribilof Islands, where multiple
observations have shown peak winds at or greater than 75 mph for
both Saint George and Saint Paul Islands. Please continue to
exercise caution as this strong storm system moves through.

Otherwise, the main story for the latter half of the work week
will be the influx of colder air behind the low, as well as a
ridge moving into the Bering Sea. These will bring much more
benign weather across the region, with the potential for snow
showers or a rain/snow mix for Southwest Alaska. How robust the
ridge is will determine how long this spell of quieter weather
lasts. Models show lows trying to encroach into the Bering Sea as
early as Wednesday afternoon, but the ridge may keep them at bay
to the west or south of the Bering Sea/Aleutian Islands. By
Thursday night, there is decent model consensus that a North
Pacific low will move across the Western Aleutians into the Bering
Sea, but the track of this low remains uncertain. Regardless,
this looks to be a much weaker system than what we`ve seen in the
past week. Stay tuned as we continue to refine the forecast.

-Chen

&&


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

Latest operational models show little agreement by Friday, so
will lean more on the ensemble means for the long term forecast. A
broad upper low positioned over the Western Aleutians looks to
slide eastward into the western Gulf by Tuesday. Upper-level jet
support should remain on the south side of the low with the
strongest winds at the surface to remain largely south of the
Aleutians. This looks to promote a quieter period of weather for
both the Bering, Southwest Alaska, and Southcentral Alaska through
the weekend. Instead, drier and cooler conditions are forecast
and lowering snow levels as a cooler airmass slowly makes its way
from interior Alaska into Southwest Alaska by Tuesday. As the low
becomes anchored over the western Gulf early next week, some
potential will exist for the return of shower chances for
Southcentral as easterly waves may bring scattered showers to the
Copper River Basin, Prince William Sound, and Gulf coastal
regions.

-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.

&&


$$