Gale Warning 30, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
450 PM AKST Wed Jan 8 2025

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Friday night)...

Currently, it is mostly quiet all across the Southcentral
mainland. The calm winds and cooler air aloft have allowed
temperatures to drop to near or below freezing for most of the
mainland with the exception of the coastal regions. However, the
warmer air mass that is in place will remain for the forecast
period, so high temperatures will likely remain near or above
freezing for much of the lower elevations in the mainland. Any
lingering precipitation from the previous episode is relegated to
the coastal mountains at this point. However, a low is moving up
the Gulf and will bring chances in the near future. Kodiak Island
is already has increasing wind speeds and precipitation chances
ahead of low, which will only increase further as the low gets
closer. This low is interesting in that its associated surface low
will split into two as it approaches the mainland, with the first
one tracking to the eastern Gulf and the second tracking just
east of Kodiak Island.

Once the low's front arrives to the north Gulf on Thursday
morning, widespread precipitation will occur all along the Gulf
coast as well as strong winds. Storm force winds are expected in
a line off the coast for a few hours until the front pushes
onshore. Due to the nature of this system, a deformation band will
form and stretch from west Alaska all the way to the Gulf. As the
low moves onshore, this band will move eastward and will pass
through the Anchorage, Mat-Su Valley, and the Kenai Peninsula,
regions from Thursday to Friday afternoon, allowing for chances of
precipitation. This will mostly be in the form of a mix of snow
and rain due to a shallow layer of warmer temperatures aloft.
However, once the core of the precipitation passes through,
precipitation may change to all snow due to wet bulbing. This is
still very uncertain and will depend on how much the temperature
profile cools before the event happens.

Afterwards, we will have a brief respite before the next low
arrives on Saturday. This one resembles the last low in its track and
will bring precipitation and strong winds to Southcentral,
potentially even to the Anchorage and Mat-Su Valley if the track
is more westerly. The coastal and mountainous regions as usual will
receive the most precipitation. Warm air advection will accompany
this low, so mixed precipitation is possible once again. Still,
all of these scenarios are highly dependent on the track of the
low and a eastward or westward shift could make a large
difference. This is only the beginning, however, as a strong
shortwave from a low in the Bering will pass through the northern
Gulf on Sunday, allowing for a potential for significant winds in
Prince William Sound that may cross into Anchorage. This is a bit
further out, so there is some uncertainty with this scenario.

-JAR

&&

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

A small, weak and vertically stacked low continues to spin in
place over the central Bering Sea this evening to the west of the
Pribilof Islands. This low is embedded within a larger scale
trough encompassing most of the Bering Sea region. A large field
of snow showers generated by cool air passing over the still
fairly warm sea surface near and southwest of the low is
continuing to affect parts of the Aleutians and Pribilofs this
morning. Across Southwest, increasing offshore flow will help to
scour out the fog in Bristol Bay this evening, however skies
tonight will remain full as a low pressure system approaches from
the Southeast.

In terms of the forecast, the expectation remains for things to
become a bit more active with time as two separate and stronger
lows begin to impact parts of the area beginning later tonight
into Thursday. By this evening, a North Pacific low entering the
Gulf of Alaska will spread northeast winds as strong as high-end
gale force into waters between the northern AKPen and Kodiak
Island. An area of deformation is still looking possible to
establish over the Bristol Bay area for a period late tonight into
early Thursday morning. A mix of rain and snow is the anticipated
form of precipitation, during this wave, however latest guidance
is suggesting a quicker alleviation of conditions, with
precipitation diminishing by later Thursday morning.

Looking to the second system of interest, a separate North Pacific
low will push its occluded front into the Aleutian Chain late
tonight, moving over the western/Central Aleutians from Adak to
Amchitka. This will likely be a gale-force front, bringing light
to moderate precipitation rates. Temperatures close to sea level
will start out cold enough for all snow to fall as the front
approaches the central/eastern Aleutian Chain, but a quick transition
to mostly rain is expected by late Thursday morning into Thursday
afternoon as the front continues to progress northeast and as
warmer air moves in behind the boundary. From Thursday night into
Friday, the parent low will cross over into the southern Bering
Sea, then continue northeast towards the Kuskokwim Delta as it
begins to weaken. A corridor of strong west to southwest winds
will follow near and south of the low as it heads northeast, with
Storm force gusts potentially impacting the eastern Aleutians on
Friday morning, depending on the exact low track and intensity.

Confidence remains low with regards to the low's track as it
approaches the Southwest coastline late this workweek. We are
monitoring the potential for coastal flooding in the Kuskokwim
Delta with onshore flow in conjunction with a high tide and lack
of significant ice coverage along the coast. However, confidence
is low with regards to the strength of the onshore flow and where
exactly the core of winds will establish. Regardless, the
potential for a push of coastal waters onshore is there, so please
remained tuned for our updated thoughts regarding these upcoming
systems and beyond.

-AS/CL

&&

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

Most of Southern Alaska will continue under a very active weather
pattern through the forecast period. The upper air longwave over
the Bering will be weakening, with the low centers moving into the
Arctic. A couple of significant shortwaves will support a
strengthening surface low in the Eastern Bering bringing heavy
precipitation and strong winds from the Central Aleutians to the
Canadian Border, and into most of Interior and Southwestern
Alaska. This low will push over Western Alaska as it tracks North.

Model guidance with the GFS and ECMWF hold decent synoptic scale
agreement through midweek, but some timing issues complicate the
locations and precipitation types expected due to strong warming
and the advection with the winds. Areas of moderate rains or rain
mixed with snow with gusty outflow winds are expected across
Southwest Alaska, and over Pribilofs and the Central Aleutians
Sunday. Most areas of rain are expected to change to snow by
Wednesday across Western Alaska. Heavy rains and high end gale
force winds are expected from the Eastern Aleutians over the
Alaska Peninsula and Kodiak Island Sunday. Higher elevations
across the Southcentral coasts will see heavy snow. These
conditions spread over the Kenai Peninsula into Prince William
Sound Sunday night before diminishing across the Southcentral
coasts and the Gulf of Alaska Monday afternoon. Another weak low
and front pushes over the Western and Central Aleutians Tuesday
and Wednesday.

&&

.AVIATION...

PANC...Northerly winds could be gusty at times overnight through
early Thursday morning. It is looking increasingly likely that
there will be a brief period of light precipitation sometime
between 12Z and 18Z Thursday as an upper level short-wave tracks
inland. The persistent northerly flow will maintain dry conditions
near the surface, so ceilings will likely remain VFR. The
atmosphere will be marginally cooler than this morning, right on
the edge of rain and snow. Precipitation type will likely depend
on intensity, with lighter more intermittent precipitation leading
to rain and marginally heavier and steadier precipitation leading
to snow. Surface temperatures will be right around the freezing
mark, so freezing rain is also a possibility. Towards the end of
the TAF period a band of precipitation is expected to move from
the Kenai P northeast into Anchorage. This would bring heavier
precipitation to the Terminal, likely bringing cigs down to MVFR
with a possibility of IFR should precipitation type be snow. There
is still uncertainty as to the intensity of precipitation within
the band.

&&