Gale Warning 29, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
547 AM AKST Sun Dec 31 2023

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today
into next year)...

The pattern over Southcentral is changing as a North Pacific low
has moved northward into the Gulf of Alaska. The front associated
with this low is warming temperatures and bringing in snow to
windward sides of the coastal mountains with just a little bit of
snow inland. With this pattern shift, the bitterly cold
temperatures should be done with for the time being for all areas
of Southcentral not called the Copper River Basin, where it will
remain mostly below zero. Otherwise, expect cloudier and warmer
conditions the next few days. The northeasterly Matanuska River
winds are expected to develop by this afternoon and will continue
into the overnight hours for Palmer and Wasilla. The pressure
gradient should relax sufficiently after midnight for the winds to
settle down by late Sunday night.

The current low can be seen on satellite extending from
Southcentral Alaska to the southeast and through the Gulf of
Alaska along the frontal band. What is also of note on satellite
is a large low that is about 850 miles due south of Kodiak Island.
This low is moving northward rather quickly and will make it a
few hundred miles southwest of Kodiak Sunday night and then stall
out as it get absorbed into a much large low tracking along the
Aleutian Chain. This low currently south of Kodiak looks to stay
a little farther south than previous forecasts which should lessen
the precipitation along the north Gulf coast Sunday night into
Monday as flow aloft will turn more to the northeast and not push
the moisture as far north. There is still a little bit of a
precipitation-type challenge for the north Gulf coast as far north
as Whittier, where elevations under 500 ft are likely to mix rain
in by Monday. However, with the low stalling out southwest of
Kodiak it should keep the air aloft colder, keeping snow for all
but the lower elevations of the immediate coastline. This may
change on Tuesday depending on how far north the third low (the
strong low that will track along the Aleutian Islands) is able to
move northward on Tuesday. The potential exists for rain to push
over the Kenai Mountains and through Turnagain Arm, but with the
main low not really pushing far to the north in the Bering Sea
until it is significantly weakened, it may blunt the impact of the
warm air progression as well. This seems to be the big forecast
challenge for late Monday through Tuesday night.

&&

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

A negatively-tilted shortwave trough is lifting north across
Southwest this morning, helping to support a band of light snow
now stretching roughly between Sleetmute and Iliamna. Occasional
snow showers are continuing on and off elsewhere, with
temperatures also now warming by 10s of degrees compared to 24
hours ago in some spots as increasing southerly flow and dense
cloud cover finally begin to push Southwest out of the deep
freeze we've seen over the past few days. Light snow ongoing near
the Alaska Range should gradually come to an end later this
afternoon as the upper support moves north into the Interior.

Attention shifts quickly from there to what is becoming more
likely to be a very prolonged, intense easterly wind event
beginning sometime on Monday. On Monday morning, a strong low
lifting out of the Pacific will move slowly closer to the AKPen as
a ridge rapidly builds out ahead of it into Mainland Alaska. This
will set up a strong pressure gradient between these two features,
and winds gusts from the east-southeast will pick up to as high as
40 mph by Monday afternoon across mainly coastal areas and parts
of Bristol Bay with enhanced flow through the Kamishak Gap. At the
same time, light snow will spread from southwest to northeast
along the coast, and this may combine with the developing gusty
winds to cause areas of blowing snow and reduced visibility at
times. However, temperatures across the region will steadily warm
with a combination of warm advection and downslope flow off of
the ALaska Range between Monday and Tuesday, and this should allow
any lingering precipitation to change over to rain (especially
towards Bristol Bay and the AKPen) and end any potential for
significant blowing snow.

By Tuesday afternoon, another very potent low moving into the
southern Bering Sea will push a strong front into Southwest,
effectively enhancing the already strong gradient and wind field
in place. Very strong gusts as high as 70 mph will be possible
with this next frontal system between Tuesday afternoon and
Wednesday morning, mainly where gap enhancement will again be most
prominent, roughly along a line running between Iliamna and
Koliganek. Uncertainty for the exact strength and timing of this
next frontal system is still on the high side, so be sure to
continue monitoring the forecast for updates as we continue to
hone in on this next impactful storm system.

-AS

&&

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

An extremely active pattern is set to continue across the greater
Bering Sea region for the foreseeable future, with a complex
pattern evolution involving three separate lows affecting each
other's trajectory expected to play out through midweek. In the
near term through tonight, a weakening low with multiple embedded
centers will continue to impact portions of the southwestern
Bering and central/western Aleutians with gusty west winds as
high as gale force along with intermittent snow/rain showers. The
low will weaken by tonight as it lifts north west of the
Pribilofs, shortly before the next two big players in the pattern
move into the picture.

By late Monday morning, a strong, storm force low will make it's
presence felt across the Aleutians as it approaches from the
southwest. Storm force easterly winds with gusts to Hurricane
force will move into the central Aleutians while temperatures
initially remain cold enough for incoming precipitation to fall as
snow, possibly resulting in near whiteout conditions at times for
Adak and Atka. The expected track of this low continues to shift
west compared to earlier projections, and this should allow warm
air near the low's center to make it into the central Aleutians
and change snow over to a rain/snow mix Monday evening before the
low crosses the Chain into the Bering and colder air rushes back
in from the northwest. There is still some remaining uncertainly
regarding how quickly the low's front will weaken as it continues
northeast into the eastern Aleutians on Monday night, with
potential for high wind to affect Dutch Harbor for a brief period
late Monday night to early Tuesday morning. Meanwhile, another
strong low will move south of the Alaska Peninsula, sending
easterly gale force winds into the eastern fringes of the Bering
Sea close to the Alaska Peninsula and Bristol Bay. This secondary
system will merge with Bering system's occluded front on Tuesday,
eventually resulting in one absolutely enormous low extending
across much of the North Pacific, Bering Sea and Mainland Alaska.
Sustained winds between gale and storm force range will affect
most of the outlook area around this system through at least
Tuesday night, except right near the center as it moves slowly
east over the southern Bering Sea.

-AS

&&

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

Longwave trough pattern changes little through the end of next
week and models continue to key in on the development of a strong
upper low over the southern Bering Tuesday into Wednesday. While
the low is forecast to peak in intensity Tuesday morning, with a
sub 950 mb surface low to track immediately west of Unalaska by
Tuesday evening, surface pressures will remain in the 950 mb range
into Wednesday as the low lifts northward and just east of the
Pribilof Islands. Gusty conditions will be prevalent across the
Bering and the Aleutians as a result with gale to storm force
winds surrounding the surface low. The pattern remains active into
the weekend with the next upper low to lift across the Western
and Central Aleutians Friday into Saturday.

Further east, persistent southeasterly flow into the Southcentral
coast will promote numerous showers with a threat for heavy rain
forecast across the Eastern Kenai Peninsula and Prince William
Sound. The Bering Sea low will bring a front across the Gulf of
Alaska Tuesday into Wednesday, which should further enhance
rainfall rates as the front tracks from west to east along the
Southcentral coast.

BL

&&

.AVIATION...

PANC..Conditions looks to remain VFR around the airport as the
next system moves into the region. There could be a brief period
of light snow this morning but even so, conditions should remain
VFR. Southeast winds aloft moving into the are will bring in the
possibility for low level wind shear this afternoon into the
evening.

&&