146
FXAK68 PAFC 190115
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
515 PM AKDT Wed Sep 18 2024

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

Pockets of heavier shower activity across the Northern Gulf Coast
this afternoon continues to slide farther east to the Panhandle
tonight as the North Gulf Coast and Prince William Sound begin to
clear out. The low pressure system causing this disturbed weather
will also continue moving east through the Gulf towards the
Panhandle. Flow behind this low will continue to be off-shore in
nature and gusty at times for areas like Seward, Whittier, and
Kodiak with the north and westerly winds. With cold air banking up
in Kamishak Gap, also expecting some gale-force winds through the
Barren Islands tonight and into the day on Thursday before the
cold air and westerly flow weaken later in the day.

While there maybe some sunshine tomorrow across most of
Southcentral Alaska, it is not expected to be widespread, but more
breaks of sunshine in between cloudy periods. This is due mostly
to continued cyclonic flow and weak upper-level shortwaves moves
through the progressive west-to-east flow. One such shortwave
looks to dig southward across much of the central interior and
into Southcentral Thursday night and Friday. This could provide
the chance at a few showers across the Susitna Valley and Copper
River Basin. Although a few snow showers or rain/snow showers mix
could be possible in the Copper River Basin late Thursday night
into early Friday morning, and again Friday night into Saturday
morning, it remains unseen if the area can cool down enough at the
surface due to the impending cloud cover associated with the
upper waves. The best chance of seeing a little mix would be
around the Eureka area. Otherwise, most wintry precipitation
should be confined over the mountains.

Additional waves also look to traverse the Gulf from west-to-east
keeping the Northern Gulf Coast and Prince William Sound
unsettled and showery Friday into Saturday. Also of note, the same
guidance trends exhibited with the North Pacific low yesterday
were also exhibited today. The current trend is for the system to
stay mostly to the south of the area and affect mostly Southeast
Alaska Friday and Saturday. The Canadian guidance continues to be
the northern outlier as this forecast package continues to depict
a more southern solution and in line with the majority of
guidance. Aside from the cloudiness of the coast for late week
into the weekend, cloudy conditions are also likely for most other
locations across Southcentral due to the influence of upper-level
waves moving through the area. Most shower activity should be
confined to the Susitna Valley and Copper River Basin through
Saturday evening.

&&


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

While stronger winds and showers will linger along Bristol Bay
and the Alaska Peninsula through early tomorrow morning,
generally colder and quieter weather is on tap as a ridge builds
in over the Bering Sea. With light onshore flow and pressure
building, it is possible that the Kuskokwim Delta, Bristol Bay,
and Alaska Peninsula could have patchy fog tomorrow morning.
While weak subsidence is likely for Southwest Alaska, there is a
low potential for embedded shortwaves to bring brief periods of
precipitation (rain, snow, or a mix) to Southwest Alaska Friday
and this weekend. This should be very minor and not widespread.

Farther west, a front accompanying a Kamchatka low is expected to
move into the western Aleutians by this afternoon. The ridge will
help slow the front`s progression, keeping rain chances likely
for the western Aleutians and much lower elsewhere. One major
change since yesterday`s forecast package is a shift in the track
of a North Pacific low. Where previous model runs had shown this
low remaining further south, more recent model runs have shifted
it north, bringing small craft winds towards the Aleutian Islands
and increasing rain chances from late tonight through tomorrow
evening.

Also by Thursday night, a low moves towards the Western
Bering Sea and Aleutians. There may still be shifts in this
low`s track, but generally expect winds primarily to small craft
speeds with gales possible for the Western and Central
Aleutians/Bering Sea. Currently, the forecast has this low
stalling out near the Eastern Aleutians Friday night as it runs up
against the ridge. We`ll see how models evolve their depiction of
the forecast but, for now, the positioning of the ridge over the
Eastern Bering Sea and Southwest Alaska will keep calmer, colder,
and drier weather over these locations while directing incoming
storms towards the Aleutian Islands, keeping this region wetter
and warmer for the coming days.

rux/chen

&&


.LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...

The upper level Alaska Weather map shows a mildly cyclonic flow
with a number of perturbations from Eastern Asia into Canada.
These support surface lows and fronts that will sweep over the
Aleutians and the Alaska Peninsula. These systems will become more
or less stationary and weaken across the Northern Gulf of Alaska
through the forecast period. A ridge over the Bering through
Monday flattens out through midweek. The ECMWF is running more
energetically with greater amplitude, so the GFS/Canadian models
are preferred. Locally heavy rains spread from the Central
Aleutians, over the AKPEN and Kodiak Island and across the Gulf
through Monday. Locally heavy rains occur over the Southcentral
coast, with lesser amounts pushing inland. The associated surface
also brings near gale force winds with gale force gusts over the
Southern Bering, diminishing Monday. Widespread gale force winds
extend along the Pacific side of the Aleutians and AKPEN. The
surface low continues into the Gulf just East of Kodiak Island,
winds intensify to high end gales and storm force gusts. Worst
conditions are expected through the Barren Island, lower Cook
Inlet and Shelikof Strait Monday, diminishing Tuesday. A gale
force barrier jet forms along the North Gulf Coast for Monday,
diminishing late.

- Kutz

&&

.AVIATION...

PANC...An upper level low sits just east of the terminal this
afternoon ans is continuing to move quickly to the east. There is
high confidence that primarily VFR conditions should prevail as
weak cyclonic flow comes through Anchorage through Thursday
afternoon, bringing some light northwest to southwest winds. A
brief shower is possible later this afternoon into early evening
due to a weak upper-level wave dropping southeast through the
Susitna Valley.

There is a small chance that the lower atmosphere is moist enough
to result in some low-lying fog tonight into Thursday morning, but
the combination of light winds keeping the boundary layer mixed
and the presence of clouds limiting radiative cooling makes it
not very likely.

Overall, things are looking good for a brief break in significant
weather from Wednesday evening through Thursday, keeping VFR
conditions through this time frame.

&&


$$