Gale Warning 706, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
405 PM AKST Thu Nov 16 2023

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

Key Takeaways:

1) Snow continues for the northern Susitna Valley. Locations
along the Parks Highway between Milepost 120 and 180 may receive
an additional 4 to 8 inches of snowfall. A winter weather
advisory remains in effect through 5PM Friday.

2) Coastal locations along the eastern Chugach such as Cordova
and Valdez should see their heaviest snow thus far this year.
Between 5 and 10 inches likely for these coastal communities.

3) The coldest air of the season will arrive on Friday and
persist through the weekend. Expect overnight lows around 0 for
the Anchorage Bowl and much of the Kenai Peninsula, below 0 for
much of the Mat-Su Valley, and below -10 for the Copper River
Basin.

4) Strong northerly gap winds will develop along the coast from
Kodiak to Seward, Whittier, and Valdez Friday through Sunday.
Thompson Pass will see blowing snow, along with the potential for
blizzard conditions, beginning early Saturday morning.

GOES water vapor imagery shows a broad upper-level trough
continuing to move slowly across the state from west to east.
Southwesterly flow and weak waves / vort maxima are moving from
Kodiak Island northeast toward the Copper River Basin. These
features are continuing to push widespread shower activity over
Southcentral, with enhanced precipitation, in the form of
snow showers, over the mountains due to persistent upslope flow.
Temperatures in lower elevations nearer the coast have remained
above freezing, leading to rain or mixed rain/snow showers.

This pattern will continue through early Friday morning, with an
additional 4 to 8 inches of snow for Hatcher Pass and the northern
Susitna Valley. Colder air wrapping in around the base of the
trough, though, will allow for temperatures to drop overnight from
south to north. Mixed precipitation will likely change to all
snow along the coast with 5 to 10 inches possible for Valdez and
Cordova for Friday.

Bands of snow showers are also expected to move through the Cook
Inlet and Mat Valley areas early Friday morning. While
precipitation is expected to move quickly through this region, a
quick inch or so of snow is not out of the question in heavier
showers.

Precipitation will then taper off from west to east through
Friday, with the exception of the Copper River Basin, as much
colder air advects over Southcentral for the weekend. 850mb temps
are expected to fall to around -15C by Saturday and to around -20C
through Saturday for the Copper River Basin. The building surface
ridge will also act to promote cold temperatures, especially
overnight in locations that manage to clear out. As mentioned
above, the coldest temps of the season are expected. Overnight
lows below 0 will occur in many locations such as the Mat-Su
Valleys and Copper River Basin. Much of Anchorage will sit within
a couple degrees on either side of 0 Fri-Sun nights.

Northerly gap winds will also be a concern as the colder air moves
in, with strong winds expected from Kodiak City to Seward,
Whittier, and Valdez. Winds combined with newly fallen snow will
also bring the potential for blizzard conditions for Thompson Pass
by Saturday morning.

-TM

&&

.SHORT TERM FORECAST SOUTHWEST/BERING SEA/ALEUTIANS (Days 1
through 3: Today through Saturday night)...

Key Messages:

-Lows in the teens and single digits with the coldest temperatures
 expected Friday night and Saturday night.

A trough has cleared Southwest Alaska and moved off to the east
this evening. Clear skies have developed in its wake with Bethel,
Dillingham, and King Salmon enjoying some sunshine on the backside
of the trough. Stratus continues to blanket much of the Lower
Kuskokwim Valley and interior portions of Bristol Bay. Any
lingering precipitation across Southwest Alaska the next few days
should be limited to orographic lift over the Kuskokwim Mountains
and Western Alaska Range. As has been advertised, much cooler
temperatures will invade Southwest Alaska through the weekend.
Overnight lows are expected to drop into the teens and single
digits, with the warmest conditions forecast along the Kuskokwim
Delta coast. Overnight low temperatures from Toksook Bay to Kipnuk
may remain in the lower 20s. In addition to cooler temperatures,
northwest winds may be gusty at times with potential wind gusts
ranging from 25 to 35 mph through tomorrow morning for Southwest
Alaska.

Further west, northwesterly flow will prevail over the Bering in
tandem with continued cold air advection from the north. The
combination of northwest flow and cooler temperatures
overspreading the "warmer" sea surface temperatures will result in
the continuation of convective snow showers through much of the
Bering. The bigger feature to impact the Bering and Aleutians
arrives Saturday night into Sunday morning. A strong front is
forecast to bring storm force, southerly winds to the Western
Aleutians early Sunday morning. Potential gusts to hurricane force
will be possible across Shemya before the axis of strongest winds
along the front lifts northward into the western Bering. Gales to
storms will be the theme over the latter half of the weekend for
the western Bering, with gales more common from the Pribilof
Islands, east.

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

The long term forecast period begins on Sunday with a cold
longwave trough over mainland Alaska producing temperatures around
10 degrees below normal and rising temperatures over the
Aleutians, Bering Sea and Southwest Alaska as an upper level ridge
builds north and east over the Western Bering Sea. Light snow
should be diminishing over the Copper River Basin and portions of
Prince William Sound, east, as the upper level trough lifts out to
the north and east. A drier air mass diving south and east with
the cold longwave trough will help to clear out most precipitation
for both Southwest and Southcentral through the weekend. The
exception will exist over the Bering where isolated to scattered
snow showers are forecast with the trough's passage. A deep
Kamchatka low then brings a strong front into the Bering Sunday
into Monday with potential high winds as the front moves through
the Western and Central Aleutians. The front will progress into
the eastern Bering by Monday with a rain/snow mix and enhanced
southerly winds along the front, from the Eastern Aleutians up
into the Chukchi Sea. A low will deepen rapidly in the Northern
Pacific and push north into the Western Gulf of Alaska on Tuesday
and Wednesday and will likely produce strong winds and heavy
precipitation along the entire Gulf of Alaska Coast on Tuesday and
Wednesday of next week.

-CC

&&

.AVIATION...

PANC...Rain and snow showers this afternoon will transition to all
snow by this evening with less than an inch of accumulation
expected. Ceilings and visibility will remain mainly MVFR but may
occasionally drop to IFR in heavier showers through the forecast
period. Temperatures will drop from the mid to upper 30s this
afternoon to around 20 by Friday morning. Gusty southeasterly
winds will continue into late tonight, diminishing and switching
to northerly after 12Z Friday morning.

-CC

&&