693
FXAK68 PAFC 141258
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
458 AM AKDT Tue May 14 2024

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

The cold upper level low responsible for showers (and a few
thunderstorms with hail) over Southcentral yesterday is exiting
south into the Gulf this morning. Vorticity-maxima rotating around
the north side of the low continue to produce isolated showers
early this morning, primarily from the Talkeetna Mountains south
to the Mat Valley and through Tahneta Pass into the western Copper
River Basin. Meanwhile, a surface low over the northeastern Gulf
is being pulled back westward toward the upper low center.
Middleton Island radar imagery shows a North-South oriented band
of rain tracking westward across the northern Gulf and
southeastern Prince William Sound, including Cordova. Further
west, mostly clear skies can be found from Kodiak Island north
to the Kenai Peninsula and much of the Susitna Valley.
Temperatures have once again dropped into the 30s, with isolated
areas down below freezing.

The upper level low will exit eastward across the Gulf today,
though cyclonic flow aloft, with embedded vorticity.maxima will
continue to transit Southcentral. Slightly warmer temperatures
in the upper atmosphere means conditions won`t be quite as
unstable today as they were yesterday. Still expect increasing
showers this afternoon, but fewer showers than Monday and no
thunderstorms. The favored areas for scattered showers will be
the Mat-Su near the Talkeetna Mountains (roughly Willow to
Palmer) along with the Copper River Basin - especially along
the Tok Cutoff and north side of the Wrangell Mountains.

An upstream ridge of high pressure will build eastward tonight,
then move overhead of Southcentral on Wednesday. This will cap
off convection and lead to widespread sunny skies and warm
temperatures. With a surface high building up from the Gulf,
expect stronger sea breezes along the coast. This will lead to
somewhat cooler temperatures for coastal communities compared
to inland areas.

A dissipating front from a deep low in the Bering Sea will
approach Kodiak Island and the western Gulf on Thursday. There
will be very little forcing left, but likely enough to produce
areas of very light rain. This will also lead to increasing clouds
across the western tier of Southcentral Thursday through Thursday
night. Model spread is quiet large with regard to the eastward
progression of the long-wave trough and handling of individual
short-waves. Thus, it is not clear whether any precipitation
will make it up to Southcentral.

-SEB

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA AND THE
ALEUTIANS (Days 1 through 3/ Today through Thursday morning)...

The building ridge over the eastern Bering continues to move into
Southwest Alaska this morning, providing calmer conditions for
much of the area through tonight. This brief period of calmer
weather will be short lived however, as a Kamchatka low in the
western Bering continues to move eastward towards the western
Alaska coastline.

The Kamchatka low`s front extends across the entire western
Bering, producing widespread gale force winds through tomorrow
morning. Warm air behind the front will cause the majority of
precipitation to come in the form of rain as the low progresses
eastward. By Wednesday morning, the range of gale force winds
will be limited mainly to Nunivak Island and the Kuskokwim Delta
before the system weakens further in the afternoon hours.
Widespread precipitation will occur along the western coastline
of Alaska through at least Thursday afternoon. With the ridge
settled over mainland Alaska by this time, there is still some
model disagreement to the eastward shift of the ridge and how
it will effect the placement of the frontal precipitation across
Southwest.

A new shortwave low is also expected to impact the western
Aleutians Wednesday night into Thursday afternoon. While the
exact timing and intensity of the system is uncertain, it does
appear that some precipitation will be likely as it moves
eastward before dissipating Thursday night.

-BS

&&

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

The long term forecast for the Southern Alaska will begin with a
ridge over the Gulf of Alaska sliding east as a shortwave trough
rounds the base of a longwave upper-level trough situated over the
Bering and moves over Southwest Alaska. Models quickly diverge
with regard to the evolution of this system, adding plenty of
uncertainty right at the beginning of the long term forecast. All
guidance has the development of a surface low near the AKPen by
Friday as the shortwave deepens. However, both the GEM and EC try
to hold onto the downstream ridging longer, driving the low and
its moisture into Southcentral. The GFS pushes the ridge south and
provides a more progressive solution with the low tracking east
with only scattered showers along the western slopes of the
interior and coastal mountains. This system then exits to the east
late Saturday.

Sunday may offer a reprieve from any extensive cloud cover and/or
shower activity across the Southern Mainland. But, again, all
models are struggling with the track of various shortwaves
embedded within the longwave trough. While guidance shows a ridge
trying to build north from the North Pacific and western Gulf,
the EC and GEM quickly move the ridge axis east over the eastern
Gulf. This solution would place the entirety of the Southern
Mainland on the back side of the ridge with the resultant
southwesterly flow lending to a more unsettled pattern with
various waves moving along the Aleutian Chain and across the AKPen
and Kodiak Island. The result would be more cloud cover and
chances for rain across the region. The GFS is the more amplified
solution, with a more northerly building ridge remaining in place
longer. This result would slow any upstream storm systems and
likely result in a more northerly storm track, keeping conditions
much more tranquil across the Southern Mainland. Given the
consistency of the GFS and a trend of the EC and GEM ensembles
leaning more toward the GFS, the long term is weighted more toward
the stronger ridge solution.

For the Aleutians and Bering, the longwave trough situated over the
region will likely keep conditions cool and unsettled through the
long term. Any ridging between storm systems would be brief, with
the best chance for high pressure over the Bering late Friday
into Saturday. Any warmer air associated with the ridge, though,
would likely result in widespread stratus and fog due to the
warmer air riding over the cold open waters.

-TM

&&

.AVIATION...

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

&&


$$