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FXAK68 PAFC 201235
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
435 AM AKDT Fri Sep 20 2024

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

The biggest forecast challenge for today through the weekend looks
to be today and how the showers respond to the digging trough
entering the area. There is an upper level trough extending out
of the Interior and over the Talkeetna Mountains and into Prince
William Sound. This trough set up a band of showers (rain or snow
depending on elevation) over the Chugach Mountains, northward to
the Talkeetna Mountains including over the Matanuska Valley. This
band is not wide, maybe 10 to 40 miles, but it has persisted
through the entire night. As of 4 AM, there is signs on the GOES
18 IR satellite imagery that this trough may finally be edging
southeastward with a upper level low circulation over the northern
Susitna Valley. This also looks to be causing the current band of
showers to enhance over the Talkeetna Mountains and diminish over
the Chugach. Here is where it gets a bit more interesting:
There is another weak wave over the north Gulf coast moving
northwestward. This wave is bringing some rain showers to the
Prince William Sound (PWS) area early this morning. The likely
outcome should be for this PWS wave to get enhanced as it
interacts with the upper level trough. Models, including the Hi-
resolution ones, vary quite a bit on how strong this enhancement
will be and how far west. There is a split on whether these
showers will creep into Anchorage from the southeast later today
or if they will dissipate before moving into the area. Even the
Kenai Mountains may see some showers, but it looks unlikely that
they will make it much farther west than the mountains on the
Kenai Peninsula so expecting Kenai, Soldotna, and Homer to have a
pretty nice day.

After the main trough moves eastward tonight, the Cook Inlet
region northward through the Mat-Su (including Anchorage) should
see skies clear out and temperatures drop to the coldest morning
temperatures so far this Autumn season. That will bring below
freezing temperatures to many of the inland areas around
Southcentral. For Anchorage specifically: the thinking is that
Muldoon and east Anchorage could even get into the upper 20s while
midtown and west Anchorage remain above freezing in the mid to
upper 30s.

Saturday should then see widespread sunshine across Southcentral.
A front will then move into the Southwestern Gulf Saturday night
and overspread Southcentral on Sunday. Kodiak should see rain by
late Saturday night and through the day Sunday.

&&


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

High pressure over the Bering Sea will work its way over Southwest
Alaska, keeping drier conditions in place through this weekend.
Cold northerly flow in conjunction with mostly clear skies will
allow for temperatures to drop into the 30`s overnight for
Southwest Alaska. The lower Kuskokwim Valley is expected to see
sub-freezing temperatures Friday night and Saturday night,
elsewhere will see a range from 34F to 38F. Since we are expecting
drier conditions, we are not expecting any snow just yet.

Unsettled weather over the Aleutians is expected through this
weekend. A gale force low over Kiska this morning tracks into the
southcentral Bering Sea where it rapidly dissipates. The low
fizzles into an open wave and absorbs into an incoming North
Pacific low by Saturday morning. The next low, also expected to be
gale force, scoots south of the Aleutian Islands through the
weekend before tracking into the western Gulf of Alaska on Monday.

Widespread small craft winds will expand across the Bering Saturday
into early Sunday and gale force winds develop over the southern
Alaska Peninsula and southeastern Bering late Saturday night. Wrap
around cold air advection will reinforce the gale force gusts,
allowing them to drag along the backside of the low towards
Unalaska. Gusts to storm force will also be possible within the
belt of higher winds, primarily north of the Alaska Peninsula
Sunday morning.

&&


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

Long wave low pressure system will dominate the early extended
outlook over most of the state and Gulf of Alaska. Models are in
good agreement with the upper level low remaining over the
northern part of the State with with associated surface features
impacting much of the Alaskan Peninsula and Gulf region. The GFS
and Canadian models move the axis of the upper level long wave
and most of its energy farther south and east than the European,
favoring the GFS/Canadian solutions. Conversely, the GFS and
Canadian models better handle the shortwave features, south of the
Aleutians and Alaskan Peninsula with the Canadian being more
aggressive with eastward speed and intensity.

Locally heavy precipitation will spread from the Central
Aleutians, over the Alaskan Peninsula and Kodiak Island and across
the Gulf through Tuesday. Moderate rain will occur over the
Southcentral coast, with lesser amounts moving inland. The
associated surface features also bring near gale force winds with
gale force gusts over the Southern Bering, diminishing on
Wednesday. Widespread gale force winds extend along the Pacific
side of the Aleutians and AKPEN through the end of the outlook
period. Ridging high pressure over the Bearing, coupled with the
fast moving shortwaves could bring marginal gale force winds and
to the central islands and Alaska Peninsula Wednesday and
Thursday.

-DD

&&

.AVIATION...

PANC...VFR conditions and light winds will persist through
Saturday. An upper level shortwave moving through Southcentral
will bring a chance for light showers Friday afternoon, but this may
be more likely over mountainous terrain.

&&

$$