Small Craft Advisory 1013, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
514 PM AKST Tue Nov 12 2024

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

The situation in Southcentral is similar to yesterday. It is calm
and clouds are clearing in the western portions of Southcentral.
There are some weak shortwave troughs passing through the region,
which are not having as much of an impact in the western regions
apart from near gale force gap winds in Kamishak Bay, Shelikof
Strait and the usual smaller gaps as well as Thompson Pass. The
eastern regions are having more impacts from these weak
shortwaves. The shortwaves are interacting with a surface low off
of Prince William Sound, which is allowing moisture to flow
northward. Due to this, precipitation is forming and is traversing
through the Copper River Delta towards the Copper River Basin and
westward towards Cordova and Valdez. There is a blowing snow
advisory out for Thompson Pass until Wednesday morning due to
snowfall and the aforementioned gusty winds. Snowfall in Thompson
Pass will range from 2 - 4 inches. Further north, snowfall is
expected to fall from Glennallen to McCarthy. The core of the
precipitation has shifted westward and now the bulk of snowfall
accumulations is expected in Glennallen South. Snow accumulations
will range from 3 to 4 inches in Glennallen South and 2 to 3
inches southeast towards McCarthy. Snowfall accumulations in
Cordova are a bit uncertain and will depend on when the
temperatures go below freezing. The trough will fully pass through
by Wednesday evening and chances for precipitation will end.

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 incoming low
will tighten pressure gradients and combined with the thermal
gradient, will allow for gusty winds to remain in Resurrection
Bay, Passage Canal, the Valdez Narrows, and Thompson Pass.
Thursday will see a large front from the aforementioned low move
into the region, raising wind speeds and increasing chances for
snow all across Southcentral. The Anchorage and Palmer areas,
however, will be delayed due to downsloping winds. There is still
uncertainty in where exactly the heaviest snowfall will fall and
the timing of this.

-JR

&&

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

An occluded front extending from Northern Kamchatka brings light
snow to inland areas of Southwest from this afternoon to
Wednesday morning. A rain/snow mix is likely for the Pribilof
Islands and Eastern Aleutians but should quickly transition to
all rain. Along the Southwest Coast, mostly snow is expected,
with a low chance for a rain/snow mix.

The next system quickly follows Wednesday afternoon, entering the
Southern Bering Sea between Tanaga and Great Sitkin Islands. It
passes over the Pribilof Islands Thursday morning and reaches the
Southwest coast between Kuskokwim Bay and Cape Newenham by
Thursday afternoon. Model spread and run to run variations
continue to dampen confidence on the track of this system,
however, the latest runs (3 of 4 models) are converging on a
common solution. As of this afternoon, 4 to 6 inches of snow are
expected for Bethel and Dillingham, with lower amounts across the
Kuskokwim River Valley and greater Bristol Bay. Coastal
communities and Bering Sea can expect all rain with a switch to
all snow by Thursday afternoon as cold air is drawn south behind
the low. By Friday afternoon, this system is anticipated to move
into the Gulf of Alaska.

&&

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

&&