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000
FXAK68 PAFC 091308
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
508 AM AKDT Tue Apr 9 2024

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

An arctic trough extends from the North Slope south to the Alaska
Peninsula this morning. This trough is anchored by an upper-level
low situated over Shelikof Strait. A series of potent shortwaves
is spinning around the low with the first driving a surface low
into southern Cook Inlet this morning with its attendant front
lifting over the southern Kenai Peninsula. These features are
producing areas of moderate to heavy snow showers, mainly from
Seward to Homer along with gusty south to southwest winds. Snow
showers are also lingering along the Prince William Sound coast
this morning as a weak wave ahead of the aforementioned front
lifts north over the coastal mountains. Areas of snow showers are
also developing along Turnagain Arm and into the southern Susitna
Valley due, in part, to the strong diffluence out ahead of the
upper low. Snow across Kachemak Bay earlier this morning has
fallen at a rate of up to 2 inches per hour. An Special Weather
Statement is out for the Homer area through 7 AM to highlight the
heavy snow and gusty south to southwest winds.

This first surface low will get pulled westward toward Kamishak
Bay later this morning as its front lifts north into Prince
William Sound and slows in its forward progression. Southeasterly
winds ahead of the front will increase through the morning for
Whittier, Portage, and Cordova. As this first system weakens, a
second low and surface front developing east of Kodiak Island
will drive to the southern coast of the Kenai Peninsula. This
feature will advect more moisture into an increasingly unstable
airmass, the result of colder air working in behind the initial
system. The result will be another round of moderate to heavy snow
showers across southern and eastern Kenai Peninsula late this
morning through late this afternoon. Several inches of snow will
likely fall from Seward to Whittier and Girdwood, with snowfall
rates again approaching 2 inches per hour. A Special Weather
Statement is out for these areas. Total snow accumulations will be
tricky given the timing of the snow falling mainly late morning
into the afternoon; temperatures in the mid 30s may limit
accumulations on area roads, with accumulations highly dependent
on snowfall rates.

As this wave lifts north, scattered snow showers will return to
the western Kenai later today and will likely develop across the
Anchorage Bowl. Again, accumulations will be tricky, with amounts
dependent on snowfall intensity. Snow showers will also fall from
Cordova to Valdez, with the highest amounts in the mountains
surrounding both communities.

By Wednesday, the upper-level low begins to weaken as it slides
southeast. Smaller, more compact surfaces lows will continue to
spin up rotating from east to west across the Gulf. Scattered snow
showers will continue along the immediate coast, but will come to
an end elsewhere.

A frontal system will push in Southwest Alaska Wednesday, reaching
the Cook Inlet / Susitna Valley area by early Thursday morning.
Light snow will overspread the area, but downsloping will quickly
develop for locations in the lee of the coastal mountains as a
triple point low tries to spin up along the now occluded front
near Kodiak Island. Multiple shortwave troughs and surface troughs
will move in behind the initial front for late Thursday into
Friday. Colder air and a more southwesterly flow ahead of the
main trough axis will allow precipitation to fill back in by late
Thursday afternoon or evening. As is always the case this time of
year, any snow and snow accumulation will be dependent on surface
winds and temperatures, especially during the height of the day.
Nonetheless, the coastal mountains will see significant snow
accumulation with this system. With a more persistent south to
southwesterly flow across the Susitna Valley, places like Hatcher
Pass and Broad Pass will also likely see significant snow
accumulation Thursday into Friday. Precipitation will likely
linger through Friday as yet more upper-level wave move over the
region out ahead of the trough axis.

-TM

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

Cold air will continue to filter south across Southwest Alaska and
eastern Bering/Alaska Peninsula. Gap wind south of the AKPen will
continue to be gusty through this afternoon and will gradually
diminish through tonight. Two lows currently exist that will be
the main upcoming weather drivers. One currently located over
eastern Russia, whose front will reach the Kuskokwim Delta coast
tonight, and a second, stronger system located near Kamchatka.
The Kamchatka front moves into the western Bering Sea tonight,
bringing a rather large area of storm force winds and widespread
gale force winds to the western/central Bering Sea. The front then
quickly moves towards the Southwest Coast by early Wednesday
morning. A hefty band of precipitation moves with the front and
much warmer air quickly follows. The Aleutians are expected to see
mostly rain with a chance for brief snow initially, primarily for
the Eastern Aleutians and southern AKPen who have been influenced
by the recent cold air advection.

Snow and winds reach the Southwest coast early Wednesday morning
and increase significantly. A Blizzard warning has been issued for
the Kuskokwim Delta, from Bethel west, for Wednesday, as wind
gusts are expected to increase to 50 mph and snow accumulation
will range from 7 to 10 inches. A Winter Weather Advisory for Snow
and Blowing Snow has been issued for the Western Capes of Bristol
Bay, including Togiak and Twin Hill for Wednesday as well, with
snow accumulations of 9 to 13 inches and wind gusts to 40 mph.
The warm air will eventually reach Southwest Alaska, however, snow
intensity is anticipated to be high enough to overcome
temperatures increasing to 33/34 degrees. The immediate coast is
the most likely to see transitions to rain during warmest
temperatures. Snow continues tracking inland by early Thursday and
values of 4 to 7 inches is possible across the lower Kuskokwim
Valley and interior portions of Bristol Bay.

&&


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

The long term forecast begins on Friday with a shortwave ridge
exiting the eastern Gulf of Alaska and a large upper-level trough
over western Alaska. As a result, low pressure at the surface
spreads across Southwest Alaska, and a surface low briefly
develops over the Gulf early on Friday. A cold air mass will
remain in place over western Alaska while also spilling into the
Gulf. As the trough digs to the east, gusty winds and
precipitation taper off across most of Southwest by Saturday
morning as northwesterly gap winds increase along the Alaska
Peninsula. The system will maintain precipitation across
Southcentral through Saturday. The upper low and its attendant
surface low will exit into Southeast Alaska on Sunday. Model
agreement really begins to diverge on Monday with an Arctic upper-
level low. A potent shortwave is advertised to round the base of
the low and enter into western Alaska, however, the exact
placement of the wave (and, thus, the attendant surface low) has
yet to be ironed out. The deterministic GFS and Canadian NH runs
are the most similar to each other, while the EC is the slowest in
bringing the shortwave to western Alaska.

AF

&&

.AVIATION...

PANC...VFR conditions and light northerly winds will persist
through around noon or so. Bands of showers will move across the
Anchorage Bowl this morning; however, with dry air in the lower
levels of atmosphere, any precipitation from these bands is not
expected to reach the ground. A southeasterly Turnagain Arm winds
is expected to bend over the terminal by early afternoon.
Redevelopment of shower activity is also expected around the same
time, with any showers falling as snow or graupel due to an
unstable airmass. Brief MVFR conditions are possible in any
showers that do develop over the terminal. Gusty southeasterly
winds and any lingering shower activity is expected to taper off
by late Tuesday evening.


&&


$$