Gale Warning 203, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
559 AM AKST Wed Feb 21 2024

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

Shortwave axis continues to push through Southcentral this
morning, with light showers continuing over upslope areas in the
Prince William Sound. Some light snow accumulations are possible
in Valdez through this afternoon. Strong gap winds have
temporarily shut off through the Turnagain and Knik Arms, while
continuing through the Copper River Valley.

A large and robust upper low over the Bering Sea will push our
next system into Southcentral later this afternoon, bringing
another round of precipitation and winds. Strong vorticity
advection and jet dynamics will allow areas of locally moderate to
heavy snowfall to overspread the region through Thursday morning.
This system is also expected to bring another round of strong
winds to Anchorage and the Mat Valley, with gusts late tonight
between 40 and 60 mph for Anchorage and the Mat Valley. There is
still notable disagreement between guidance regarding the track
the surface low associated with this system will take, with these
discrepancies leading to higher uncertainty in precipitation type
and amounts in and near the Anchorage area. There is likely to be
downsloping through early tonight due to the strong southeasterly
winds, but precipitation is expected to fill in as cold air
advection increases and winds turn southerly/southwesterly. For
now, light snow accumulations are expected in the Anchorage Bowl,
with slightly higher amounts of up to 8 inches possible on the
Hillside.

Areas of higher forecast confidence for snow totals include the
Susitna Valley, northeastern Mat Valley near Sutton, and along the
Richardson Highway from Thompson Pass north to Tonsina. Please see
the associated Advisories/Warning for those areas.

The bulk of the precipitation ends by Thursday evening as the
main shortwave pushes through, but some light upslope
precipitation and showers will remain. While the exact details are
uncertain at this time, another shortwave swinging around the
main upper low will bring another round of precipitation to
Southcentral for Friday into Saturday.

-ME/CJ

&&

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

Active weather remains on tap for Southwest Alaska, the Bering
Sea, and across the Aleutians through the rest of the work week.
As a strong low moves across the Bering Sea this week, strong
winds and widespread ocean-effect snow showers are likely for the
Pribilofs, the Aleutians, all the way to Southwest Alaska.

Key Messages:

Snow for Southwest
* Winter Weather Advisory for the Kuskokwim Delta and Nunivak
  Island was upgraded to a Blizzard Warning through this
  afternoon. Mekoryuk on Nunivak Island was observing quarter mile
  or less visibility with heavy snow and gusty winds. Expect
  winds gusting as high as 50 mph, visibility reduced to quarter
  mile or less along the Kuskokwim Delta Coast and Nunivak Island.
  Away from the coast, one-half mile visibility is expected.
  Total snow accumulations around 2 to 3 inches.

High Winds for the Aleutians
* High Wind Warning is in effect for the Western Aleutians,
  including Attu, Shemya, and Amchitka through Wednesday.
  Anticipate southwest winds 50 to 75 mph with gusts up to 85 mph.
  Expect snowfall to reduce visibility to quarter mile or less at
  times. Snow totals around 2 to 4 inches through tonight.

* High Wind Watch was upgraded to a High Wind Warning for the
  Central Aleutians including Adak and Atka this evening to
  Thursday morning. Expect southwest winds 40 to 60 mph with gusts
  to 80 mph. Expect reduced visibility with blowing snow. Around
  two inches of snow is expected through tonight.

Discussion:

A deepening Kamchatka low is approaching the Western Aleutians
this morning. Cold air advection around the low will help ramp up
these winds, and any snowfall would be able to blow around and
reduce visibility. Highest winds are expected through this morning
for the Western Aleutians with high confidence. As the low
progresses eastward, significant wind gusts will continue through
Adak and Atka in the Central Aleutians. Confidence has increased
for the upgrade to a High Wind Warning, however, there is still a
potential for the strongest winds to be situated just north or
west of Adak. Regardless, these strong winds for both the Central
and Western Aleutians can be potentially damaging with power
outages possible and the addition of snowfall will likely reduce
visibility, making any travel difficult.

Another round of snow for much of Southwest is expected with
gusty south to southeast winds. Observations at Mekoryuk this
morning are showing a prolonged period of blizzard conditions.
This is expected to also reach the Kuskokwim Delta Coast. The
Winter Weather Advisory was upgraded to a Blizzard Warning. The
rest of the Kuskokwim Delta away from the coast could still expect
visibility to a half mile or less. Toward Bristol Bay, winds and
blowing snow will lead to reduced visibility to a half mile or
less is expected and a Winter Weather Advisory has been issued.
The heaviest snow, up to an inch per hour later this morning, is
expected around Dillingham, Aleknagik, west to Togiak, the
windward side of the Kuskokwim mountains, including New Stuyahok
and Koliganek. Warmer air is expected for King Salmon, Iliamna,
and the Alaska Peninsula and while reduced visibility is not out
of the question, any reductions would be brief and a prolonged
period is not likely. This frontal passage is not anticipated to
be a long duration event as snow will gradually taper off through
the evening on Wednesday. It is also worth noting that Aniak and
other portions of the Lower Kuskokwim Valley could see brief
periods of reduced visibility due to snowfall and transportable
snow from gusty winds expected through this afternoon. Low
confidence remains for its potential to reduce visibility to a
half mile or less for any prolonged period.

-VR/NM

&&

.LONG TERM FORECAST (Days 4 through 7: Friday through Monday)...

A complex low over the Bering will send a series of shortwave
troughs across the Aleutians and into the mainland Alaska through
Saturday. Quasi-zonal flow late in the week will begin to
transition to more meridional as a low deepens over the Gulf and
trough starts to dig into the western Bering. In between these
systems, ridging will become more amplified as it moves over the
Aleutian Chain before dampening out once it translates into the
Gulf. These disturbances will bring locally heavy precipitation to
much of the Aleutian Chain, AKPen, Southwest and portions of
Southcentral. Warmer temperatures on the Pacific side should allow
for more rain or a rain/snow mix with rain/snow to all snow to be
found on the Bering side where much colder temperatures will
reside. As these colder temperatures continue to push across south
and east, more areas will see precipitation change over from rain
or a rain/snow mix to all snow as the weekend progresses.

&&

.AVIATION...

PANC...Another round of strong winds will develop late this
afternoon, reaching peak intensity late tonight as a low pressure
system moves up the Inlet. With the persistent southeast winds,
ceilings and visibilities are expected to remain VFR throughout
the day today. Winds will diminish as precipitation arrives early
Thursday morning. Precipitation may begin as rain due to warm near
surface temperatures, but should transition to snow as cold air
moves up the inlet. Ceilings and visibilities may to drop to MVFR
or IFR levels during this period.

&&