Gale Warning 142, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
421 AM AKST Wed Feb 28 2024

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

A deep and cold trough is centered over mainland Alaska and the
Gulf of Alaska, anchored by a vertically stacked low over the
eastern Gulf offshore. 850mb temperatures range from around -10
degrees Celsius along the north Gulf coast to -25 degrees Celsius
as you reach the Alaska Range. While this is an impressively cold
airmass (though not uncommon for this time of year), strong wind
flow around the Gulf low combined with tight surface pressure
gradients and resultant gap winds are leading to widespread windy
conditions across Southcentral. This is causing surface temperatures
to remain elevated far above what they otherwise would be with
light or calm winds. Air temperatures are fairly homogeneous in
the teens to 20s. The Copper River Basin is the one exception,
with temperatures in the single digits below zero to single digits
above zero. Wind chill readings range from single digits below
zero to teens above zero, with colder readings in the Copper River
Basin and through mountain passes. Wind speeds are highest
through the typical coastal bays and passes. Satellite-based winds
show the strongest winds over the western Gulf/Kodiak Island
coastal waters, with Storm force winds in the Kamishak Bay to
Barren Islands corridor.

The big story for the remainder of the work week will be more of
what is described above: cold and windy conditions. Short-waves
tracking down the back side of the trough across western Alaska
will move into the western Gulf and western Southcentral, with
forward momentum stopped by opposing flow around the north side
of the Gulf low. These will bring reinforcing shots of Arctic air.
The Gulf low will slowly weaken over the next couple of days,
ultimately dropping south into the Pacific by Friday. Even though
surface pressure will be rising over the Gulf, it will also be
rising over mainland Alaska. Thus, pressure gradients will remain
persistently tight. There will certainly be some fluctuations in
the strength of winds over the next couple days, but there is
enough forcing that nearly the entire region will experience
gusty winds and cold wind chills. The one notable change made to
the forecast this morning was to slow the drop in air temperatures
(because of the persistent windy conditions). Based on this
latest forecast it looks like the vast majority of Southcentral
will remain below the wind chill advisory threshold (-40 degrees
Fahrenheit with 15mph or greater sustained wind). Area mountain
passes are the most likely to ultimately reach this value.

Winds will begin to diminish Friday through Friday night as the
last in a series of short-waves moves through and a high amplitude
ridge approaches from the Bering Sea. Despite a moderating
airmass (warming 850mb temperatures), lighter winds will likely
result in the coldest temperatures of the week on Saturday morning
- with widespread sub-zero temperatures (Fahrenheit) expected.

SEB

&&

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

A strong upper level ridge is now beginning to build into place
across much of the Bering Sea ahead of what will soon be a
significant system of interest currently sitting well south of
Kamchatka. This low is already beginning to push a warm front into
the far western Aleutians, where gusty east winds and rain/snow
are in the process of shifting from the North Pacific into the
southwestern Bering. Across the rest of the outlook area farther
east, strong northwest flow is continuing to draw down Arctic air
into Southwest and through the AKPen as temperatures now begin to
dip below zero across the Lower Kuskokwim Valley and Kuskokwim
Delta. Strong gap flow up to storm force continues to blast out of
bays and passes along the AKPen, and these winds will continue to
stay strong and gusty for the next few days. Heavy to locally
extreme freezing spray rates will continue to be a marine hazard
close to the ice edge for the next couple days due to very cold
air temperatures coupled with the strong northerly winds. Out west
of Saint Matthew, a small polar low has developed this morning and
is beginning to move southeast. This low will pass north of the
Pribilof Islands later today before it heads into the southern
AKPen and shears apart, and this will likely lead to a brief
uptick in winds as it moves past along with a short period of snow
and blowing snow for the Pribilofs.

As bitterly cold air continues to settle over Southwest, attention
begins to turn towards a robust frontal system expected to take
shape and move slowly and steadily northeast into the Bering
through Friday. This front will be associated with the low
currently sitting in between Kamchatka and Japan, but the parent
low will likely stay mostly west of the outlook area as it heads
steadily north over the next few days. A surge of deep southerly
flow and very warm Pacific air is expected to commence today
behind the northward advancing front, initially allowing a quick
change from rain to snow along the frontal zone as it progresses
northeastward into the Bering and moves past the central/western
Aleutians through Thursday morning.

Later on Thursday, a nose of warm air aloft above freezing may
begin to override the very cold air mass in place over the eastern
half of the Bering Sea, setting the stage for a messy wintry mix
of precipitation transitioning from snow and sleet, then freezing
rain, then rain as the front approaches the Pribilofs, eastern
Aleutians and southern Alaska Peninsula between Thursday and
Friday. There is still a fairly high degree of uncertainty in
terms of the timing of this transition for any given location, but
the possibility of accumulating freezing rain amounting to as
much as 0.1 to 0.2 inches is becoming more likely at some point
between Thursday and Friday, especially along the southern AKPen
and across the eastern Aleutians. This will be highly dependent
on how long surface temperatures can remain at or below freezing
before warmer air moves in and changes precipitation over to
predominantly rain. The Pribilofs meanwhile could get several
inches of snow mixing with sleet and freezing rain at times, with
strong southeast winds likely to cause areas of blowing snow
between Thursday and Friday as well.

-AS

&&

.LONG TERM FORECAST (Days 4 through 7) Saturday through Tuesday...

Model tracks and strengths become more uncertain through the
forecast period. The weather pattern across the region is
dominated by moderately high amplitude troughs and ridges
traveling from West to East. A strong upper level trough over the
Central and Eastern Interior exits into the Canadian Provinces for
Sunday. On its heels is a upper level ridge that moves into the
Mainland by Tuesday. This draws a considerable amount of subzero
Arctic air all the way down to Southcentral and Southwest Alaska
through the weekend. Gusty outflow winds are expected along the
Southcentral coast and through Bristol Bay on Saturday.

In the West, a fairly strong low enters the Western Bering on
Sunday and tracks across the Northern Bering through Tuesday.
Widespread gusty winds with areas of gale force gusts spread over
the Southern Bering and Aleutians, diminishing late Monday, before
a second developing low approaches the Western Aleutians for
Tuesday. This low will bring another round of widespread gusty
winds with areas of gale force gusts spread over the Southern
Bering and Aleutians late Monday into Tuesday. Both lows deliver
locally heavy precipitation through Tuesday.

Kutz

&&

.AVIATION...

PANC...VFR conditions will persist. Gusty northerly winds will
continue for the next several days. The strongest winds are
expected this afternoon and evening when gusts could reach up to
35 kt.

&&