252
FXAK68 PAFC 271226
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
426 AM AKDT Sat Apr 27 2024

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

We start off the weekend with a front over the western Gulf and
Kodiak Island with upper level ridging building into Southwest and
Southcentral Alaska. While the ridge is not terribly strong and
upper level temperatures remain cool , it will be enough to keep
sunny skies over much of Southcentral and even clear out Kodiak
Island tonight as well. There are two subtle changes developing in
the forecast as compared to yesterday. The first is that a surface
trough will develop along the north Gulf coast tonight into
Sunday. This may increase the winds in Valdez and Seward overnight
and then keep the sea breeze out of these areas for much of
Sunday.

The second item is increasing instability over the Copper River
Basin on Sunday and how far west showers are able to develop. This
is due to a very weak upper level trough that extends out of the
Interior and over the Wrangell mountains. This trough will
strengthen enough overnight that it should cause some showers
over the elevated terrain of the Copper River Basin Sunday and
Sunday night. The question is how far west these showers will make
it. The latest hi-resolution models are showing the possibility
that there could be showers over the Talkeetna Mountains Sunday
afternoon and evening as far west as Hatcher Pass. This is
reasonable due to the cold air aloft and the potential for the
south and southwest slopes of the mountains, which have lost a
lot of their snow, to create an elevated heating source to kick
off these showers. At this point they look to be just a few
showers and there does not look to be enough lift for
thunderstorms. However, this is a change from yesterday with the
increasing chance for this to develop. On Monday, that upper
trough will head into the Yukon and take the showers with it.
Monday will also see a general increase in cloudiness across
Southcentral as the weak upper level ridge breaks down.

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Tuesday morning)...

Low pressure in the vicinity of the Shumagin Islands continues to
weaken and exit south to the North Pacific today. Northerly flow
on the backside of this low will be the main weather player today
for the southern Alaska Peninsula (AKPEN) today and into the day
on Sunday. The best chance of rain/snow shower mix will be today
into this evening for Nelson Lagoon, Cold Bay, and False Pass as
left over waves from pass overhead from the decaying upper low in
the North Pacific. Meanwhile, showers taper off across Bristol Bay
and the Kuskokwim Delta early this morning with dry weather
expected the rest of today through most of the short-term period
on Tuesday as an upper-level ridge builds over the area. The
exception would be a few scattered showers around the foothills
and terrain of Bristol Bay, the Kuskokwim Delta, and the Lower
Kuskokwim Valley for Monday as the ridge retreats eastward.
Further to the west, the front of a weak low pressure system
moving eastward through the North Pacific may clip portions of the
Aleutian Chain, southern AKPEN, and Shumagin Islands Sunday and
Monday bringing some scattered showers to those areas.

The next notable weather-maker arrives Monday morning to the
western Aleutians as a North Pacific low lifts northward and sends
its front to the east. Sustained gale-force winds are likely for
the marine areas of the western Aleutians Monday and for the
central Aleutians by Tuesday. The dominant precipitation-type with
this system will be rain. However, as the storm occludes, colder
air will work back in and there could be a change-over to
rain/snow mix on Tuesday, especially for the western Aleutians.

&&


.LONG TERM FORECAST (Days 4 through 7: Mon through Thu)...

An upper level trough will be situated over the southern Alaska
Peninsula by Tuesday morning, crossing into the southwestern Gulf
of Alaska, and a new upper level trough entering the western
Bering Sea behind it. A building ridge is expected to remain
situated over Southcentral Alaska. Through Tuesday, the ridge
will likely extend from Southcentral into Southwest Alaska
following the departure of the AKPen trough, while the western
Bering system pushes a front across the Aleutians, likely reaching
Unalaska by late Tuesday. The front is expected to generally
weaken as it approaches Southwest and the resident ridge, but the
parental low pressure system behind the front will likely move
over the Western and Central Aleutians through Wednesday.

By Wednesday afternoon, the ridge over southern Alaska may begin
to weaken as the upper-level support shows signs of shifting out
of the area. This may allow for influence from the Bering low to
move into Southwest Alaska and even Southcentral Alaska as the
system approaches by late Thursday. Gauging impacts from this
low in Southwest and Southcentral is still precarious given the
uncertainty regarding the ridge movement, as well as the
location/progression of the low itself. Model agreement regarding
the progression and potency of these systems is not good, leading
to a general uncertainty regarding timing the several fronts and
lows to enter the Bering and move through the area. However,
given the prolonged shift towards warmer weather over the next
week expected, impacts from this system will likely not be winter
weather. Although the overall synoptic setup is in fair agreement
for the extended period, the details could mean bigger differences
in the QPF and wind fields across the Bering and Southwest
Alaska.

-CL

$$

.AVIATION...

PANC...VFR conditions and light winds will persist.

&&
$$