Small Craft Advisory 1102, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 AM AKST Wed Dec 13 2023

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

A high amplitude, negatively tilted longwave trough continues to
sit over Southwest Alaska, extending southeast over the western
Gulf of Alaska. Multiple shortwaves and compact surface lows are
moving northwest ahead of of the trough axis, bringing rounds of
showery precipitation along the immediate coast and coastal
mountains this morning. Farther inland, a weak mid-level trough
extends across Cook Inlet and is the focus for lingering areas of
light snow this morning. The areal coverage of snow has expanded
overnight as moisture from a surface low over Seward advects over
the western Kenai Peninsula.

This area of snow will linger through mid-morning before moving
west with the trough. The upper-level low will then lift north to
the eastern Kenai this afternoon as a secondary surface trough
over the northern Gulf lifts into Prince William Sound. This
boundary, along with the attendant upper-level support, will push
bands of snow showers from the northern Gulf over the
Southcentral coast through this evening. Instability will increase
as these feature move north, allowing the potential for bands of
moderate to heavy snow showers to persist from Cordova east to
Whittier and Portage.

A second surface trough then moves from Middleton Island into
Prince William Sound for Thursday morning as yet another compact
surface low and upper-level shortwave lift north from the western
Gulf toward Seward. These features will pump more moisture into
Prince William Sound and over the eastern Kenai Peninsula Through
Thursday afternoon before the upper-level trough and surface
features move back to the south toward Kodiak Island. Again,
stout moisture advection and building instability will likely lead
to bands of heavy snow showers for the aforementioned locations.
While it will be difficult to pinpoint where these bands set up,
any location that sees constant banding of snow showers will
likely see several inches of accumulation. Gusty north winds,
along with areas of blowing snow, are also likely Thursday morning
from Moose Pass south to Seward if the low takes a track due
south of Resurrection Bay.

Elsewhere, northwesterly high-end gales and storm force gusts
continue from Kamishak Bay south across Shelikof Strait and the
waters surrounding Kodiak Island. These winds will slowly
diminish through the next day or so as the cold air advection from
the northwest shuts off.

Westerly winds and gusts are also likely this morning across
Kachemak Bay, Homer, and the Homer Bluffs along with occasional
bands of snow showers. These winds should diminish slightly and
turn more northerly by this afternoon or evening.

TM

&&

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

A large low pressure center in the northern Gulf of Alaska and a
col in the central Bering Sea has been promoting a strong
southerly push of cold air across the Eastern Bering Sea. The
presence of cold air and a tight pressure gradient between the two
atmospheric features has been allowing for strong gusty winds
across the southern portion of the Alaska Peninsula and the
Eastern Aleutians. Bands of snow showers moving in along with
these strong winds has promoted widespread areas of blowing snow,
and for areas along the southern Alaska Peninsula, reducing
visibility to one half mile or less at times. Southern Alaska
Peninsula may see additional snow accumulations of 3-5 inches with
locally higher accumulations possible due to training bands of
snow showers. Winds are expected to reach peak intensity early
this morning, tapering down slightly this afternoon, and gradually
easing overnight Wednesday into Thursday. Snowfall will similarly
diminish overnight into Thursday morning.

The system that will eventually break the hold of this cold air
flow will be a new low pressure system pushing in from the western
Bering sea. This low pressure system will be initially noted by a
leading frontal passage that will bring warmer southerly air
arriving to the western-most Aleutians by Wednesday morning. The
front will bring with it another round of precipitation, however
this will likely come in the form of liquid rain due to the warmer
temperatures. The front will be produce Gale-force southerly
winds with some Storm-force winds possible further north into the
Central Bering sea, however will likely be less "gusty" in nature
due to the temperature of the air coming in being warmer than
whats currently in place. The front will advance steadily
eastward, reaching Unalaska by Thursday morning. As the front
approaches, precipitation may initially begin as snowfall, but is
expected to transition within a few hours to plain rain. There is
the possibility for areas such as the Pribilofs, which may hold on
to some of the cold air in place, may see primarily snowfall and
with the strong southerly flow, may see some periods of blowing
snow. By this time, the tight pressure gradient driving strong
winds through the Eastern Aleutians will have relaxed, and the
strong winds eased significantly. By Thursday morning, the
parental low pressure center will enter the Western Bering sea,
re-initializing the precipitation over the western- most
Aleutians, however this time likely in the form of snowfall due to
more colder air entrained in the system.

Friday morning the front will make it's approach to Southwest
Alaska, bringing a high influx of moisture to the area. Cold air
has taken a firm grip over much of Southwest Alaska and will be
resistant to the warm southerly push from the front. It is
currently expected that temperatures across Southwest Alaska,
especially along the coast, will see relatively warmer
temperatures, however still remain below freezing. As such, as the
moisture moves in with the front it is currently expected to
bring a surge of snowfall to coastal communities such as
Dillingham, Togiak, Bethel, and Kipnuk. Through Friday and into
Friday evening, there is the possibility for snowfall totals to
reach up to a foot, with the larger totals expected near Cape
Constantine. There will also likely be a push of gusty
southeasterly winds along these areas, bringing the possibility
for blowing snow and reduced visibility Friday to Southwest. There
is currently a large spread of model solutions, and agreement is
sparse, so it is currently difficult to determine exactly how
impactful this push will be. We will continue to monitor this
system as it makes it's approach across the Bering Sea this week.

CL

&&

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

A broad upper level trough stretches across the Bering into
Western Alaska, with a number of significant shortwaves rotating
along the trough through the period. A deeper trough over the
Bering Saturday puts much of Southern Alaska in moist Southerly
airflow. This stronger shortwave will extend the trough through
the Gulf of Alaska for Monday and then inland Tuesday, and
develops a couple of surface lows in the Gulf, bringing more
significant weather to the Southcentral portions of the state.
Precipitation begins as snow, with locally heavier amounts on the
Alaska Peninsula West of Kodiak Island, and from the Kenai
Peninsula across to the Canadian Border Sunday through Tuesday.
This changes to rain as the lows approach the coast. Areas of snow
spread inland to the foothills of the Alaska and Talkeetna
ranges, and through Prince William Sound into the Copper River
Valley. Increasing winds remain mostly offshore, but stronger gap
winds are expected around Kodiak Island up to Prince William Sound
Sunday through Tuesday.

The Bering Sea and Aleutians stay active Saturday through Monday
as shortwaves pivot around the main trough And spread into the
Alaska Peninsula. An additional low coming from Kamchatka looks to
send its gale force front from the western Aleutians Sunday
afternoon to the central Aleutians by Monday morning and further
East through Tuesday. This will spread gusty winds and
precipitation all along the Aleutian Chain to Bristol Bay through
the first part of the week.

Kutz

&&

.AVIATION...

PANC...MVFR conditions should persist through morning with
isolated -SN possible through 18z. Conditions improve during the
afternoon to low end VFR after 18z with lingering VCSH possible
through 00z. Winds should remain from the N through the TAF
period, with sustained winds between 5-8kts decreasing to 2-4kts
by 06-10z. With saturated air mass under calm winds, potential for
IFR ceilings and FG development by 06-10z, with eventual return
to snow showers by 12z tomorrow morning.

&&

Preliminary Local Storm Report
National Weather Service Anchorage AK
953 AM AKST Wed Dec 13 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0922 AM     Snow             Upper Hillside          61.12N 149.72W
12/13/2023  M16.0 inch       Anchorage          AK   Public

&&

CJ

Preliminary Local Storm Report
National Weather Service Anchorage AK
954 AM AKST Wed Dec 13 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0950 AM     Snow             Elmore and De Armoun    61.10N 149.82W
12/13/2023  M12.0 inch       Anchorage          AK   Public

&&

CJ

Preliminary Local Storm Report
National Weather Service Anchorage AK
1038 AM AKST Wed Dec 13 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1034 AM     Snow             Big Lake                61.51N 149.95W
12/13/2023  M6.0 inch        Matanuska-Susitna  AK   Public

&&

CJ

Preliminary Local Storm Report
National Weather Service Anchorage AK
1053 AM AKST Wed Dec 13 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1052 AM     Snow             Lake Otis and 80th      61.15N 149.83W
12/13/2023  M11.0 inch       Anchorage          AK   Public

            3.5 overnight.

&&

CJ

Preliminary Local Storm Report
National Weather Service Anchorage AK
343 PM AKST Wed Dec 13 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0300 PM     Snow             Upper Potter Valley     61.06N 149.76W
12/13/2023  E7.3 inch        Anchorage          AK   Trained Spotter

            0.17 inches liquid equivalent.

&&

KC

Preliminary Local Storm Report
National Weather Service Anchorage AK
346 PM AKST Wed Dec 13 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0300 PM     Snow             Upper Potter Valley     61.06N 149.76W
12/13/2023  M7.3 inch        Anchorage          AK   Trained Spotter

            Corrects measurement precision of previous
            report. 0.17 inches liquid equivalent.

&&

KC