Gale Warning 199, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
607 AM AKST Tue Feb 20 2024

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

A ~975mb low continues to push northward over the Alaska
Peninsula and further inland throughout the day today. A strong
south/southeasterly flow and moisture plume continues light to
moderate rain across Southcentral, with typical downslope areas
remaining mostly dry. A strong pressure gradient between this low
and an upper ridge over the eastern Gulf continues strong gap
winds through the Turnagain and Knik Arms and south Copper River
Valley. While the main Turnagain Arm wind core will remain south
of Anchorage, occasional gusty winds are still expected throughout
the day, especially across south and west Anchorage.

As the low continues to decay over southwest Alaska through this
evening, the main shortwave axis and its front finally push
through early tonight, allowing the strong gap winds to come to an
end. Cold air advection and up inlet flow may allow precipitation
to fill in briefly and end as a mix or snow across the Western
Kenai Peninsula, Anchorage Bowl and Mat Valley. Precipitation will
continue to linger near the Prince William Sound with Valdez also
experiencing a transition to snow. Light to moderate
accumulations are likely there starting tonight and will also
continue in Thompson Pass ahead of the next system.

As we approach the latter half of Wednesday into Thursday, a
large and robust upper low over the Bering Sea will push another
system into Southcentral, bringing a period of widespread
precipitation. This system will be notably colder, so the threat
of moderate to heavy snow returns across portions of Southcentral.
Light accumulations are expected in the Anchorage Bowl, with
slightly higher amounts up on the Hillside. The highest amounts
will be in and near the Chugach Range, with 1 to 2 feet of heavy
wet snow possible in Valdez and up to 3 to 4 feet in Thompson Pass
late Wednesday into Thursday.

-ME

&&

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

Key Messages:

Snow for Southwest
* Winter Weather Advisory remains on track for snow and blowing
  snow in Bristol Bay through 11 AM and for snow in the Lower
  Kuskokwim Valley through 4PM AKST.

High Winds for the Aleutians
* The High Wind Watch was upgraded to a High Wind Warning for the
  Western Aleutians, including Attu, Shemya, and Amchitka, from 10
  PM AKST (9PM HST) tonight through Wednesday 9PM AKST (8PM HST).
  Southwest winds gusting up to 85 mph is expected. Snowfall could
  reduce visibility at times too.

* The High Wind Watch remains in effect for the Central Aleutians,
  including Amchitka, Adak, and Atka, from Wednesday afternoon
  through Thursday. Southwest wind gusts up to 70 mph is likely
  with 80 mph remaining possible.

Discussion:

Accumulations up to six inches of snow is expected for the lower
Kuskokwim Valley through this afternoon. Snow will begin to taper
off later this morning for the Bristol Bay area and then this
afternoon for the lower Kuskokwim Valley. Reduced visibility to
half mile at times with blowing snow was reported for Koliganek
and New Stuyahok this morning, where northerly winds allowed the
air to remain cold enough for snow. East of Koliganek, warmer air
and rainfall was reported for easterly winds through the Kamishak
Gap, including King Salmon and Iliamna. As easterly winds turn
northerly and westerly, temperatures will cool and switch any
liquid precipitation back to snow.

A strengthening low is approaching the Western Aleutians. Models
have slowed the progression of this low, but strong winds are
still expected. Cold air advection behind the cold front is
expected to aid in increasing winds throughout the day today.
Snow showers could reduce visibility significantly at times before
the peak winds arrive after midnight into Wednesday morning.
Southwest wind gusts up to 85 mph is expected. The High Wind Watch
for this area was upgraded to a Warning. The Watch remains out
for the central Aleutians as confidence remains lower for the
Adak and Atka area. The core of strongest winds is expected to
move east and widespread areas of 70 mph gusts is likely, but the
location and timing for when those winds decrease is playing a
factor in where the strongest winds relative the Aleutians will be
located.

The leading occlusion and warm front extending from the
low is progressing east today with wind gusts to 45 mph. The
Pribilofs could have a period of mix precipitation around
midnight. St Paul will more likely remain snow. This front will
reach the Southwestern Alaska coast for Wednesday morning and
could bring another round of snow for Southwest. The heaviest snow
is pointed toward Dillingham, Aleknagik, west to Togiak, the
windward side of the Kuskokwim mountains, and along the Kuskokwim
coast. As cold air advects across the Bering Sea behind the
frontal passages, convective snow showers is expected through the
better part of this active week.

&&

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

The upper level low in the Bering weakens and begins an easterly
track through Interior southcentral Alaska. It forms a weak
center over the Gulf Sunday morning, and dissipates by Monday
morning. The tightest gradients remain along the Southern
periphery propelled by a generally zonal jetstream. Transient
fronts and troughs will bring locally heavy precipitation across
the Aleutians, AKPEN and Southwest Alaska. Precipitation will be
mostly rain on the Pacific side, with mixed rain and snow or all
snow on the Bering side through Friday. Temperatures cool back
below freezing over the weekend, expanding the areas of snow
through Monday. After a shortwave ridge transits the Bering,
another upper level low moves out of the Russian Far East.

&&

.AVIATION...

PANC...Gusty southeasterly Turnagain Arm winds are expected to
persist across the terminal throughout the day today. Ceilings
will lower to around 4,000 ft through this evening, but should
remain VFR. The strong southeasterly winds will shut off as a
front moves through around midnight but it may bring a period of
rain and snow for a few hours, potentially reducing visibility to
MVFR.

-ME

&&