Gale Warning 291, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
520 PM AKDT Sat Mar 16 2024

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

The forecast remains on track with precipitation currently ongoing
this afternoon across the Prince William Sound, the Copper River
Basin, and a band of light snow setting up over Cook Inlet from
the western Kenai Peninsula into the Susitna Valley. Some areas
along the Prince William Sound coast had transitioned over to
rain by late morning. Valdez still remains in snow despite being a
two to three degrees above freezing. They are still expected to
transition gradually over to rain tonight and tomorrow as warm air
advection is still expected to continue into next week.

The band over Cook Inlet is expected to gradually shift east to
Anchorage, Willow, and Talkeetna after midnight tonight and Sunday
morning. Confidence remains low on when and how long the snow
band lingers as it moves eastward into Monday morning. A ridge is
expected to move into Southcentral by Monday afternoon, however,
that will help clear out any lingering snow.

Models break down again around Tuesday morning with the timing of
the next front approaching Kodiak Island from the west Tuesday
morning with the NAM being the outlier with timing at this time.

&&

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

The weather remains very quiet across the Bering Sea, Aleutians,
and Southwest Alaska. An upper level ridge which has been sitting
over the heart of the Bering Sea has begun to retreat north and
west, allowing a high amplitude trough with embedded upper level
low to shift westward from mainland Alaska into the Bering Sea.
However, there is very little cloud cover associated with the
upper trough. A strong surface high over the Alaskan Arctic
(~1048mb) and low pressure over the North Pacific (~1000mb just
south of the Aleutian Chain) along with weak cold air advection
between the upper ridge and upper low is leading to persistent
northerly winds and dry air advection. Thus, Southwest Alaska
remains mostly clear and cold. Afternoon temperatures are once
again hovering in the single digits for much of the Kuskokwim
Valley and Kuskokwim Delta. Winds are strongest along the
Kuskokwim Delta (as high as 30 mph), leading to wind chill
readings as low as 25 degrees below zero. As winds blow off
the ice edge in the northern to eastern Bering Sea, bands of
stratocumulus quickly develop, containing light snow showers
and gusty winds. An old frontal boundary and upper trough are
strung out along the Aleutians, producing no more than a few
rain and snow showers.

A significant change in the weather pattern remains on track for
Sunday night through Monday. This will be the beginning of a
prolonged period of storm systems tracking from south to north
from the Pacific to the Bering Sea. After multiple weeks of
northerly flow in the eastern half of the Bering Sea along with
a significant southward advance of the sea ice, southerly flow
will bring a much warmer regime and both push sea ice back
northward and begin to break up and melt ice along the southern
edge. Models have been fairly consistent with track of the first
storm, with just some minor adjustments in track and timing,
which are reflected in the latest forecasts. The eastern
Aleutians (including Unalaska/Dutch Harbor and Akutan), southern
Alaska Peninsula (including False Pass, Cold Bay, and King Cove),
the Pribilof Islands, and the Kuskokwim Delta will see the
greatest impacts of strong southerly winds and rain Monday
through Tuesday. Southerly winds will be particularly strong
through gaps in the Aleutians and Alaska Peninsula (such as Unimak
Pass, False Pass, and Cold Bay). The Kuskokwim Delta will see
some snow and blowing snow as precipitation arrives Monday
afternoon/evening - especially along the coast. Flow will shift
to southerly overnight, likely causing temperatures to jump above
freezing. Since the antecedent airmass is extremely cold, will
likely need to issue an Advisory or Warning for reduced visibilities
in snow and blowing snow as precipitation first arrives. Meanwhile,
confidence is much higher that Bristol Bay and the Kuskokwim
Valley will remain dry for this first storm.

The first storm will rotate northwestward across the Bering Sea
Tuesday, with a new storm coming in from the Pacific farther west
along the central to western Aleutians. This storm looks quite a
bit weaker than the first storm, with just a narrow band of gale
force winds and precipitation along the leading frontal system.

&&

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

The long term forecast remains largely unchanged. The upper level
pattern will be highly amplified, featuring deep troughing over
the Bering Sea and Aleutians and a stout ridge across much of
Mainland Alaska and the Gulf. This large scale weather pattern
will favor warmer than average temperatures across Southern
Alaska. While drier weather and lighter winds are expected for
Southcentral Alaska under the ridge, much more active weather will
be in store for the Bering Sea, Aleutian Islands, and Southwest
Alaska as several storms move through. The biggest challenge in
the long term will be honing in on the track and evolution of
these storms, which will then inform where the strongest winds
(likely to gale force or higher) and heaviest precipitation are
expected. Forecast uncertainty increases by Friday among the
operational global models. There are hints that an incoming
shortwave will be strong enough to impact the ridge, but models
diverge on whether the weakened ridge will remain over
Southcentral, or if it will be displaced into Canada.

- KC

&&

.AVIATION...

PANC...MVFR ceilings Saturday afternoon will continue to lower
but remain just above IFR this evening and are expected to remain
just above IFR through Sunday morning. Visibility in light snow
will drop to MVFR conditions this afternoon and remain MVFR
through Sunday morning. Winds will remain light mainly from the
north Saturday afternoon and will shift to the southwest Saturday
evening through Sunday morning.

-CC

&&