Storm Warning 171, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
419 AM AKST Wed Nov 13 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Wednesday through Friday evening)...

An upper-level trough situated over western Prince William Sound
this morning will continue to move east through the Copper River
Basin this afternoon. The shortwave is interacting with a
weakening surface low south of Cordova, which is allowing moisture
to be pulled northward toward Cordova and points north. Widespread
light snow over the Copper River Basin will continue into the
early afternoon hours before ending as the trough exits the
region. An additional 1 to 2 inches of snow is possible from
Glennallen south along the Richardson and Edgerton Highways. For
Thompson Pass, persistently strong gap winds through the pass
will allow for blowing snow to continue for the next several
hours.

Some brief ridging will follow, setting up for a quiet Wednesday
night across the region. Wednesday night will be quite cold with
temperatures dropping below zero for the Copper River Basin and
the Susitna Valley. Temperatures could fall to the single digits
in the Anchorage Bowl and the Kenai Peninsula. The tight pressure
gradient and cold air advection will allow for gusty winds to
remain in Resurrection Bay, Passage Canal, Valdez Narrows, and
Thompson Pass through Thursday morning.

By Thursday morning, a front attached to the strong low in the
eastern Bering will move into the Western Gulf and across Kodiak
Island with rain and gusty winds. The front will then move to the
northern Gulf by Friday morning. As the front tracks northeast,
precipitation will overspread the region from Cook Inlet and the
Mat-Su valleys west into Prince William Sound. With plenty of
cold air in place ahead of the front, precipitation will start as
snow. The uncertainty in the forecast will be the orientation of
the front as it moves into Prince William Sound and whether the
expected strong winds around Whittier and Portage pull in enough
warm at near the surface to change snow to rain late Thursday
night or early Friday morning. Right now, it looks like just
enough warm air might make into coastal locations from Homer to
Seward, Whittier, and Cordova for a changeover to rain followed by
some light snow accumulations. For the Cook Inlet region, places
from Ninilchik to Nikiski and into southern and western Susitna
Valley may see several inches of snow accumulation through Friday.
For Anchorage and the Mat Valley, a southeasterly wind aloft may
limit the amount of moisture spilling over the coastal mountains,
with only around an inch of snow possible. For Portage Valley and
Turnagain Pass, the combination of snow and wind, at least
initially, may produce a period of blowing snow. Several inches of
snow is also possible for Valdez and Thompson Pass with this
system.

A new surface low will develop along the front somewhere near
Seward Friday morning. As this low moves toward Prince William
Sound, the gusty southeasterly winds will quickly wind down and
shift back to the northwest. This may allow a band of snow to
redevelop over Cook Inlet and the Anchorage Bowl for late Friday
into Saturday with light snow accumulations as the storm begins to
move east and the upper-level trough lifts north of the region.

-TM

&&

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

The next low pressure system arrives today, entering the southern
Bering Sea over the Andreanof Islands this morning and crossing
just south of the Pribilof Islands tonight. High end gales and
storm force winds will make their way across the Central and
Eastern Aleutians and the marine areas surrounding the southern
Alaska Peninsula. Models have been inconsistent over the last few
days regarding the track of this low as it approaches Southwest
Alaska and have only recently started consolidating towards the
southerly track, pushing the low near the Western Capes/Kuskokwim
Bay by early Thursday afternoon. Some model discrepancies remain
by Thursday afternoon, especially for the Greater Bristol Bay
area, whose potential for snow and/or blowing snow concerns will
be heavily dependent on the low track. The Kuskokwim Delta coast
and Nunivak Island look particularly susceptible to blizzard
conditions at worst and blowing snow concerns at best, while
inland areas towards Bethel are less likely to see blizzard
conditions but still likely to see some blowing snow. The Western
Capes are in a sweet zone where they may stay warm enough to be
all rain or a rain/snow mix, which will help negate
blizzard/blowing snow concerns. Higher concerns, storm track
willing, will be areas impacted by Kamishak Gap winds, including
Dillingham north to Koliganek and east to Kokhanok, who may see
some blowing snow Thursday morning. Snow will spread inland into
the lower Kuskokwim Valley by Thursday afternoon. Snow
accumulations of 6 to 10 inches are possible between early
Thursday morning and early Friday afternoon.

&&

.LONG TERM FORECAST (Days 4 through 7: Saturday through
Tuesday)...

By the start of the weekend, the triple-point low formed from the
Bering/North Pacific low will be centered over the northern Gulf
of Alaska. Heavy precipitation will persist along the Gulf
coastline, ranging from the eastern Kenai Peninsula to Prince
William Sound. Light snowfall will also occur over interior
Southcentral before dissipating over most locations by Sunday
afternoon. Portions of Southwest and the eastern Aleutians will
see periods of snow through Sunday night as a few weak shortwaves
pass over. In addition, a compact shortwave low will move over the
western and central Aleutians on Sunday, producing gale-force
winds and another round of precipitation for the chain. The low
will move eastward before situating itself over the southern Gulf
by Tuesday afternoon.

The big story for next week will be the potential for a
significant drop in temperatures over mainland Alaska. Behind the
triple-point low will be a digging trough that will bring frigid
air over the area. Current guidance is suggesting low temperatures
on Monday and Tuesday to drop below zero, with areas over the
Copper River Basin and Kuskokwim River valley potentially
dropping past -10. Continue to follow for updates as we get closer
to this event.

&&.AVIATION...

PANC...Some vicinity fog may linger through the morning hours on
Wednesday as it advects southward over the Knik Arm. Otherwise,
VFR conditions and light winds will persist.

&&