Small Craft Advisory 151, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
507 PM AKST Wed Feb 14 2024

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

A strong blocking ridge is centered over the southern Yukon and
extends across most of the Gulf and Southcentral, with dry air
(due to subsidence) noted in water vapor imagery. This is
producing clear skies across all of Southcentral. A surface low
is located around 400 miles south of Kodiak Island and the Alaska
Peninsula, with a warm occlusion extending northward to Bristol
Bay. Pressure gradient driven east to southeast winds extend
across the western Gulf and western portions of Southcentral. The
combination of gusty winds and warm temperatures in the first 5000
feet of the atmosphere (as per the 12Z Anchorage sounding) is
leading to some balmy temperatures out there, with readings in the
40s to 50s from the Kenai Peninsula to Anchorage and the
Matanuska Valley. Wind sheltered areas and those portions of
Southcentral closer to the ridge center are cooler, with
temperatures in the 20s to 30s. Kodiak Island is right along the
periphery of moisture from the Pacific storm, with mostly cloudy
skies and steady light rain near the south end of Kodiak Island.

The upper level ridge will slowly shift eastward across western
Canada over the next few days. For Southcentral, there will be
very little change in weather for the next couple days, with
continued sunny skies, windy conditions in many areas, and warm
temperatures. Kodiak Island will see periods of rain, locally
heavy at times, as the ridge retreats and a series of lows and
upper level short-waves track northward out of the Pacific.
The retreating ridge will bring clouds and precipitation northward
across the Gulf on Saturday. There are some differences in model
guidance, but expect precipitation to reach the eastern Kenai
Peninsula and Gulf coast sometime this weekend - as early as
Friday night or as late as Saturday night. Snow levels will start
out near 1000 feet and rise through the weekend, so expect all
rain at sea level as precipitation arrives. With continued
southeasterly low level flow, inland areas will remain downsloped
and mostly dry.

-SEB

&&

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

A highly amplified pattern, with a deep longwave trough extending
across the Bering Sea into the North Pacific and a robust closed
anticyclone centered over southern Yukon, is drawing a southerly
moisture tap across the Alaska Peninsula into mainland Southwest
Alaska this evening. The abundant moisture, combined with cold air
entrenched across the Bering Sea, is leading to moderate snowfall
for much of the Alaska Peninsula and portions of Bristol Bay and
the Kuskokwim Delta. This band of snow will sweep slowly westward
tonight, spreading snow as far west as the Kuskokwim Delta coast
and False Pass, with areas to the west (such as Nunivak Island and
the eastern Aleutians) likely to remain dry. Expect snow to
combine with northerly winds right on the threshold for blowing
snow to reduce visibility to one half mile in the Kuskokwim Delta
west of Bethel, while stronger winds across the southern Alaska
Peninsula will lead to a more widespread low visibility threat
there as snow arrives and increases in intensity this evening.
Expect both impactful snow accumulations and blowing snow to
continue for the Kuskokwim Delta, portions of Bristol Bay, and the
Alaska Peninsula through Thursday morning, at which point snow
will begin to taper off. For more details, such as expected
snowfall amounts, see the relevant Winter Weather Advisory in
effect for each of these areas. In the wake of the first round of
snow, southeasterly winds will bring in warmer air, with
temperatures rising into the 30s.

A second round of snow will develop for the same areas as a
second shortwave trough lifts across the Alaska Peninsula Thursday
afternoon and evening. This round of snow is included in the
aforementioned Winter Weather Advisories for Bristol Bay and the
Alaska Peninsula, where blowing snow will be less of an issue but
impactful moderate snowfall will still be possible through
Thursday night. Snow is expected to be the predominant
precipitation type due to persistent cold air aloft, despite the
warmer forecast surface temperatures. Precipitation becomes
downsloped out in the southeasterly flow with the lack of
significant forcing or abundant moisture, allowing much of Bristol
Bay and the north side of the Alaska Peninsula to remain fairly
dry.

Further north in the Kuskokwim Delta, a lighter intensity, but
longer duration snowfall event will set up as the trough axis
remains parked over the eastern Bering Sea. There, light snow will
be likely to continue, especially along the coast and including
Nunivak Island and the Western Capes of Bristol Bay through
Saturday, leading to an additional 4 to 8 inches of snowfall
beyond the first round of 4 to 10 tonight.

By Friday night and Saturday, a front lifting out of the North
Pacific will begin to spread another round of precipitation into
Bristol Bay and the north side of the Alaska Peninsula. This air
mass looks to be warmer than the previous ones, so rain may begin
to mix into Bristol Bay.

Out west, the Aleutians and western/central Bering Sea remain
mostly quiet. A North Pacific low lifts northward over the
western Aleutians bringing snow and gusty winds through Thursday.
The front then makes it to the Central Aleutians by Thursday and
weakens into Friday morning. A stronger North Pacific low looks to
impact the Western Aleutians/Bering by Friday, bringing storm
force southeasterly winds. The front looks to make it to the
Central Aleutians by Friday night as it weakens. There is still
some uncertainty on the exact track, with some uncertainty in
potential high winds across the western Aleutians on the south
side of the low for Saturday. Stay tuned as the forecast is
further refined.

-CQ

&&

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

The upper level Canadian ridge extending over Mainland Alaska
briefly regains its amplitude before edging to the East through
Wednesday. A weak upper level low in the Gulf of Alaska drifts to
the Southeast through Monday, while the Bering low loops around
the Central Bering. Several significant shortwaves rotate around
this low through the end of the forecast period. Forecast
confidence is overall good, however it briefly becomes chaotically
uncertain locally as the shortwaves move along the Southern
portions. One shortwave over the Western Aleutians and Bering
brings areas of gale force winds for Sunday, diminishing.
Afterward, it helps develop a weak closed center South of the
Eastern Aleutians Tuesday that moves into the North Pacific by
Wednesday. Precipitation along the Aleutians and Alaska Peninsula
starts as snow and becomes mixed rain and snow on the Bering side
and all rain along the Pacific side through Wednesday. Another
well developed low approaches the Western Aleutians for Wednesday,
increasing winds and precipitation in the West.

The Bering shortwaves batter the Western side of the Mainland
ridge as the ridge begins its Eastward move. Surface wind flow
will boost moisture all along the Southern Coasts from the bottom
of the Alaska Peninsula and Kodiak Island into Cook Inlet, and
from the bottom of the Kenai Peninsula to the Canadian Border.
Coastal locations will see rain with the higher amounts from
Prince William Sound East as somewhat warmer than normal
temperatures continue to pump into the Interior through the
forecast period.

-Kutz

&&

.AVIATION...

PANC...VFR conditions and light northerly winds will persist
through the TAF period. The light northerly winds surface winds
combined with Turnagain Arm increasing again this afternoon and
tonight will produce the possibility of LLWS into Thursday
morning.

-CC

&&