Winter Weather in Alaska, November 17, 2023

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
433 AM AKST Fri Nov 17 2023

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

Key Takeaways:

1) Coastal locations along the eastern Chugach such as Cordova and
Valdez will continue to see additional snowfall through the morning
before tapering off by this evening.

2) 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.

3) 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 gradually
shifting eastward across much of the mainland. The associated
surface trough is now elongated across the Cook Inlet and into the
Mat-Su Valley. Radar imagery shows that bands of snow showers have
developed across the Cook Inlet and into the Kenai Peninsula.
Additional radar returns can be seen on the north side of the Cook
Inlet trough, with snow wrapping around the trough and into the
Mat-Su Valley. A quick inch or so of additional snowfall can't be
ruled out this morning in any stronger bands of snowfall such as
one that just went through Kenai. Otherwise, snowfall amounts will
generally be light (<1 inch) for much of southcentral.

Slightly heavier snow will continue on the downstream side of the
mid/upper-level trough across the eastern Chugach and from Valdez
east through Cordova. Additional snowfall upwards of 5 inches is
expect for these areas, with lower totals closer to sea level.

Precipitation will then taper off from west to east today 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 Saturday
before eventually subsiding late Saturday Night into Sunday morning.

-Brown / TM

&&

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

Most of the Bering Sea and Southwest are now dominated by
relatively weak west to northwest prevailing flow through most of
the troposphere. A deep upper trough is now exiting Southwest as
it crosses over the Alaska Range into Southcentral, while a
shortwave ridge crosses the central/eastern Bering Sea. Mostly
weak winds in small craft range or lower are now prevailing across
the Bering and along the Aleutian Chain, while gusty northwest
winds over Southwest slowly begin to diminish as cold advection
weakens and Arctic air slowly settles into place.

Nearly the entire region will continue to see fairly benign
conditions for about the next day or two. Widespread ocean effect
snow showers generated by cold air moving over the comparatively
warm sea surface will continue to drift into the Aleutians and
Alaska Peninsula, as well as along parts of the Southwest coast at
times. This shower activity will be further aggravated as a
shortwave trough crosses the Bering from northwest to southeast
between this afternoon and Saturday morning, resulting in more
widespread snow showers brushing past the Pribilofs, Kuskokwim
Delta and Bristol Bay overnight tonight, then into the
central/eastern Aleutian Chain on Saturday morning. Otherwise, the
main story to tell through Saturday will be the cold temperatures
persisting over Southwest. Low temperatures will likely be the
coldest early on Saturday, dipping into the single digits
above/below zero away from the immediate coastline.

Attention from there shifts to the next notable weather maker
arriving out in the western Bering Sea later in the weekend. By
Saturday night, a deep 940s mb low moving east of Kamchatka will
send a very strong front into the western Bering Sea and
Aleutians. Sustained winds well into storm force range will move
first into Shemya and Attu, then progress east with the front
towards the central Bering and out to Adak on Sunday as the core
of strongest winds weakens slightly. Gusts to Hurricane force are
likely to affect the far western Aleutians and Bering as the front
approaches between Saturday night and Sunday, including in Shemya.
In addition, winds will ramp back up again over the southwest
corner of the Bering late on Sunday as the front's parent low
approaches from the south. Make sure to continue to monitor the
forecast for updates and possible headlines for this strong wind
event as this system draws nearer.

AS

&&
.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...MVFR ceilings are possible at times throughout the day
today. Winds should continue on a downward trend through the early
morning. There is a slight chance for some snow flurries early
this morning but chances decrease significantly by late
morning/early afternoon.

KM

&&