Gale Warning 828, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
506 AM AKST Fri Dec 16 2022

.ANALYSIS AND UPPER LEVELS...

The shortwave trough that helped enhanced the most recent snowfall
event across Southcentral yesterday has finally pushed across the
AlCan border into the Yukon this morning. Upper level ridging has
begun to build back overhead in its place, with the main ridge axis
now extending from the Gulf across Southwest and up into the
Bering Strait. Much cooler temperatures have filtered into
Southcentral with cool northerly flow developing in the low
levels, particularly across the Copper River Basin, where some
places have dipped into the -10s to -20s. Areas of fog aided by
moisture added to the lower atmosphere from the recent snowfall
has affected several interior valleys overnight, including around
Palmer, Anchorage and Kenai.

Out west, conditions are similarly cold and quiet across
Southwest, with mostly light northeast winds at the surface and
some upper cirrus fanning out overhead around the upper ridge in
place. A weakening warm front is progressing northwest into the
western Bering, with a plume of warm, moist air in the 30s and 40s
moving in behind it across the eastern Aleutians, southern Alaska
Peninsula and Pribilof Islands. A broad region of easterly winds
mainly in small craft range is enveloping most of the Bering, with
a smaller region of low end gales moving between St Matthew Island
and the Pribilofs.

&&

.MODEL DISCUSSION...

Models are in generally good agreement with the large-scale
pattern through early next week. However, there are some key
details still unresolved for a shortwave trough expected to drop
into Southcentral from the north between Saturday and Sunday. The
NAM/GFS are currently depicting a much more amplified wave driving
south more quickly compared to the Canadian and ECWMF solutions,
with the NAM and GFS also showing a more west track over the Kenai
Peninsula and Cook Inlet region by Sunday morning. The stronger
and more progressive solution for this trough would result in gap
winds picking up sooner through the Matanuska Valley and down the
Cook Inlet between Saturday afternoon and Sunday morning, with
winds also peaking at a higher intensity. Differences also remain
apparent for a series of easterly waves moving across the
Aleutians and western Bering through Sunday, but the overall
impact to the forecast is more minimal.

&&

.AVIATION...
PANC...Areas of fog and low stratus with associated IFR conditions
should erode as the morning progresses, as a drying northerly flow
continues to take shape. There is some uncertainty regarding how
long the moist layer trapped at the surface will hold on, but
still expect any lingering low stratus and mist to clear out by
around Noon today at the latest. Winds will remain light and
northerly for the duration of the TAF period.

&&

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

A high pressure ridge to the west will keep Southcentral in clear, cold
and dry northerly flow through the short term. However, with the
cold air over the relatively warmer waters of Cook Inlet and
radiational cooling has allowed for fog and stratus to form from
Kenai north to Anchorage, the Matanuska Valley and southern
portions of the Susitna valley. This fog and stratus is expected
to dissipate by late morning through the early afternoon hours as
dry northerly flow and cold air advection scour out the moisture.
Temperatures will cool each day as the inversion strengthens and
cold air advection continues. As the inversion strengthens
temperatures on the hillsides and higher elevations will be
warmer than the valleys. On Sunday a shortwave will dive south
across the Southcentral. This will allow for strong winds to
develop from Thompson Pass and Valdez, as well as the Copper
River Delta. Blowing snow is likely around Thompson Pass and
Valdez, which could cause significant reductions in visibility
due to the recent snowfall.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Sunday)...

The forecast remains on track; little has changed as high pressure
continues to build over Southwest Alaska. Frigid temperatures,
windy conditions, and mostly clear skies will be on tap through
Sunday. With southeasterly flow in the Bering helping to pump in
warm air and moisture from the North Pacific, coastal regions of
Southwest Alaska and the Alaska Peninsula will have a greater
chance of seeing some clouds and slightly warmer temperatures than
the remainder of the region. In particular, the Alaska Peninsula
from about Pilot Point south is squarely within this southeasterly
flow and will see temperatures climb into the 30s and 40s as well
as increasing rain chances.

&&

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

The forecast remains on track. The main story for the Bering Sea
and Aleutians continues to be strong winds, warming temperatures,
and rain showers. High pressure over Mainland Alaska and low
pressure near the Kamchatka Peninsula and in the North Pacific
will lead to a persistent swath of southeasterly small craft winds
through the Bering Sea. As upper level shortwaves transit
overhead and the North Pacific low nudges northward on Saturday,
expect a broad area of gusty gales along the Central and Eastern
Aleutians and increased rain chances along the Aleutian Chain. By
Sunday night, a low near Kamchatka will push its front into the
Western Aleutians and Bering.

&&

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

Ensembles depict weak high pressure over the state of Alaska on
Sunday with a broad upper low just west of the Aleutian Islands. A
tightened pressure gradient between the two features would
contribute to enhanced southeasterly winds across the bulk of the
Bering, including gales west and northwest of the Pribilofs.
Through the the next several days the same Western Aleutian low is
forecast to amplify considerably while propagating eastward into
the North Pacific and well south of the Eastern Aleutians. Broad
cyclonic flow around the low may stretch from the Southeast Alaska
Coast, across the Gulf of Alaska, and over the entirety of the
Bering by Wednesday as a result.

Ultimately, this would favor continued dry and cooler conditions
over mainland Alaska through the 4 to 7 day period with drainage
flow through the usual channels along the coast of Southcentral
from Prince William Sound into the Kenai Peninsula. Over the Gulf
of Alaska, the AKPEN, the Aleutians, and the Bering, a more
unsettled pattern will prevail with cloudiness and potential
scattered showers of rain and snow. By the end of the period on
Wednesday, some operational models are showing a northward moving
front track into Southwest Alaska and the Kenai Peninsula with
increasing snow, but current timing is highly uncertain and the
front's arrival could potentially hold off until Thursday or speed
up to an earlier time.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Dense Fog Advisory: 101, 111, 121.
MARINE...Heavy Freezing Spray Warning: 160, 181.
         Gale Warning: 155, 160, 165, 170-175, 179, 412-414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AS
SOUTHCENTRAL ALASKA...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KC
LONG TERM...BL