791
FXAK68 PAFC 191334 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
529 AM AKDT Thu Sep 19 2024

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

The powerful low that tracked across the southern potion of the
state the past few days has now moved on shore and into Canada.
The final impact from it around the Gulf is some sea heights
which are still at small craft advisory levels today. With the
next low southwest of Kodiak and looking to take a track across
the far southern Gulf and then into the eastern Gulf,
Southcentral is under some ridging today which has helped clear
out skies from Kodiak through Cook Inlet and to Prince William
Sound. These clear skies have dropped temperatures into the 30s
in many locations that have not been that cold so far this
season. However, all is not clear skies mostly due to the upper
level pattern. The 500 mb trough associated with that strong low
is near the AlCan border early this morning, and while it is
moving eastward, another short wave can be seen on satellite
moving through the northern Susitna Valley and into the Copper
River Basin. While this short wave should mostly bring just some
cloud cover to these areas today, a stronger wave will move into
the Susitna Valley and to the Copper River Basin tonight into
Friday. This wave will tap into some low level moisture from the
Gulf and bring in some rain and snow showers tonight into Friday
night for the Talkeetna Mountains southeastward into Prince
William Sound as the Copper River Basin. This is where most of the
forecast uncertainty lies for tonight into Saturday.
Precipitation type is beginning to become more of a question this
time of year and higher elevations along the highways, such as
near Paxson and near Eureka may see the rain mixing with or
turning to snow during the overnight hours. Any accumulations are
expected to be light at this time, but it does bear watching. The
Prince William SOund region will be all rain.

How far east this wave dig will also make a big difference for
whether Anchorage and the Matanuska Valley will showers along the
mountains for Friday or if it will clear out Friday night into
Saturday morning and bring below freezing temperatures to east
Anchorage and colder areas such as Willow and the Butte. The
western Kenai Peninsula should be mostly clear Friday night so
Kenai, Soldotna, and other colder areas will likely get below
freezing Friday night into Saturday morning.

&&


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

Generally colder and quieter weather is on tap for most of the
Bering Sea and Southwest Alaska as a ridge builds in over the
Bering Sea. While dry weather and 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
the Kuskokwim Valley Friday through this weekend. This should be
very minor and not widespread.

Farther west, a front accompanying a Kamchatka low is lingering
over the western Aleutians and western Bering Sea. Progression of
the front is being suppressed by the ridge over the Bering Sea,
keeping rainfall likely over the western Aleutians until Friday
morning. South of the ridge along the Aleutian Chain, a surface
low is moving eastward. Chances for rain showers could skirt the
eastern Aleutians this morning, but models have continued to trend
the low more south so little precipitation is expected. With the
ridge in place and its strength dictating the synoptic flow, a
series of troughs moving toward the Aleutians will be diverted to
along this Aleutian track. The next low approaching the western
Aleutians arrives tonight and deflects eastward, spreading
precipitation to the central Aleutians before quickly dying off in
the southern Bering Sea for Friday night. Yet another, stronger
low tracks behind the previous for Saturday morning. Precipitation
is likely for Saturday across much of the Aleutians. Models are
in reasonably good agreement for the low center to track east
along the Chain, reaching the Alaska Peninsula for Sunday and into
the Gulf of Alaska by Monday. The Pribilof Islands should remain
mostly dry until Saturday night when chances increase to around 30
to 40 percent. Precipitation on Sunday will depend on how quickly
the former low dies off in the southern Bering and then also on
the low center position of the weekend system shifting slightly
north or south. Winds are expected to be stronger with this
weekends low. Small craft winds increase to gales over the weekend
near the eastern Aleutians and Alaska Peninsula. Storm force gusts
out of the north and northeast are possible near Unalaska Sunday
morning.

rux

&&

.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...There is high confidence VFR conditions prevail to the
weekend. There is a small chance for low-lying morning fog early
this morning, but light winds mixing the boundary layer are making
it more unlikely.

&&


$$