Gale Warning 894, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
542 AM AKST Mon Dec 30 2024

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

Cool, calm, and climatologically normal weather persists across much
of Southcentral Alaska as the region remains underneath the
influence of strong upper-level ridging whose axis now extends
from Yukon through east-central Alaska. Still and stable air
coincident with a strong mid/upper-level subsidence inversion has
allowed the fog/stratus deck across much of the Copper River Basin
to persist and flourish underneath otherwise ideal conditions.
The ever so high-resolution (0.75km) VIIRS Nighttime Microphysics
imagery shows the footprint of this stratus/fog covering
everything between and including Chistochina, Eureka, Glennallen,
McCarthy and the majority of the Copper River Valley along with
the many topographic tendrils. Although gloomy, the temperatures
remain significantly moderated underneath this deck with
observations farther north such as Paxson and near Mentasta Lake
recording values between -20 and -30, much warmer than those
locations, underneath the insulating blanket are recording temps
within a few degrees of 0 Fahrenheit.

Farther west, quiet weather prevails from the western Kenai
Peninsula north through Anchorage and into the Mat-Su. Unlike the
Copper River Basin where temperatures are dependent on cloud cover,
temperatures across the aforementioned parts are highly dependent on
the wind. In places such as Skwentna and Willow and even by the
Knik River where mixing has remained absent, lows overnight have
dropped below 0. Breezy northeast flow out of the Matanuska River
Valley in response to the rather (horizontally-) stacked pressure
gradient coincident with a weak shortwave trough aloft has
maintained sufficient mixing to keep temperatures as warm as the
20s.

Farther south towards and into the Prince William Sound, PAIH
(Middleton Island) Radar shows light persistent showery activity in
the northern Gulf of Alaska and southern Prince William Sound, with
relatively moist southeast flow advecting this activity into the
eastern Kenai Peninsula. Observations note these showers have made
it to Whittier and as far west as Portage. Given the light and
showery nature of the snow, along with temperatures hovering around
the freezing mark, accumulation should be pretty light... with
potential of an inch or so in Portage and perhaps even Turnagain
Pass or Alyeska by late afternoon before this activity tapers off
(50% probability of an inch through the end of the day).

The main show over the next few days across this domain will be
across the Gulf of Alaska and Kodiak Island where several rounds of
rainfall are expected through the first half of the week along with
strong gale and storm-force winds. GOES satellite imagery shows a
series of features in the north pacific approximately 500-600
miles south of the AK Peninsula as of 4am: 1) A weakening ~990mb
low impinging upon the frontal boundary draped across the western
Gulf of Alaska yesterday 2) a much stronger ~970mb low to its
southwest, and 3) a new low developing at #2s triple point. The
first low will open up into a wave today and move towards Kodiak
Island, with a gale-force wind field expanding in coverage due to
a strengthening pressure gradient between these features and the
ridge of high pressure off to the east. Features #2 and #3 phase
together later today and then bring another wave of rainfall
(high-elevation snow) to Kodiak Island tonight that'll persist
through Tuesday and into Wednesday. Precip totals for the Kodiak
City area, as well as on the southern part of the island by
Akhiok, will generally be in the 1.5- 2.0" range, with much higher
amounts in the windward mountains.

As the low shifts west, another trough will move across the Gulf
of Alaska on Wednesday, bringing widespread precipitation to the
coast with temperatures cold enough to allow for light snowfall in
some areas. Wind speeds across the Gulf of Alaska will begin to
abate on Wednesday and continue that trend on Thursday in wake of
these systems. Meanwhile, inland regions will remain spared from
both the precipitation and winds. For those hoping for snow in
Anchorage, prepare to remain underwhelmed.

-Brown

&&

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

A strong low over the northwestern Bering is continuing to track
west to northwest toward Russia this morning. Winds across the
Pribilofs should diminish substantially throughout the day.
Extending from this low is a front that curves through the
northern Bering Sea near St Lawrence Island and then stretches
across the eastern Bering Sea, along the southwestern Alaska coast
and across the Alaska Peninsula. Gusty winds and added moisture
along the front will continue bring snow showers and the potential
for blowing snow for the western Capes, the Kuskokwim coast, and
Nunivak Island through tonight. The front looks to weaken Tuesday
and drag westward, nearing the Pribilofs and south by Tuesday
night as high pressure from the Mainland strengthens and presses
west into the central Bering Sea through midweek. Along with it,
scattered light showers and northeasterly winds to around 20 mph.

Under high pressure, most of Southwest Alaska can expect a
cooling trend to temperatures over the next few days with offshore
flow and clearing skies, at least through the Kuskokwim Valley
and Delta. Bristol Bay could remain more partly to mostly cloudy
with offshore flow. Showers are expected to linger for the Alaska
Peninsula to about Unalaska through at least midweek. South of the
eastern Aleutians, a tightly wound up low is developing in the
North Pacific this morning with a relatively weaker trough
slightly ahead of it. These features are expected to slowly
meander northeast and then toward the Unimak Pass, between the
eastern Aleutians and Alaska Peninsula Tuesday night and Wednesday
morning.

Along the rest of the Aleutian Chain, rain and snow showers are
moving from west to east this morning. Showers will decrease
tonight through Tuesday as a narrow ridge builds over the central
Aleutians from about Nikolski to Adak. Broad troughing with
embedded weak disturbances near the western Aleutians will
maintain light cyclonic flow as winds gradually shift south and
then east today through Tuesday. Winds may be variable at times
across the western and central Aleutians and these weak
disturbances interact with a pressing ridge from the east.
However, a stronger North Pacific low is expected to encroach onto
the western Aleutians around Thursday morning. Its front will
lift parallel to the Islands though its progression could be
stunted by the projected high pressure over the northern half of
the Bering Sea.

rux

&&

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

A broad, upper-level ridge extending from the western Canadian
Provinces across Mainland Alaska and continuing into the Russian
Arctic through most of the forecast period. The ridge is briefly
interrupted by an upper level arctic trough slipping over the
Yukon Territory on Friday, and re-establishes itself Saturday.
Widespread dry and colder conditions prevail over most of the
Alaska Interior. The cold outflow brings some gusty winds into the
northern Bering that will merge with another system from the
Southwest Friday. An equally elongated trough stretches from
eastern Asia over the Aleutians and Bering into the Gulf of
Alaska, supporting a series of surface lows and fronts through the
weekend. Jetstream support of the storm tracks remains well South
of the Aleutians through the forecast period. Blended ECMWF/GFS
and Canadian models carry the features through Sunday.

A weakening low center South of the Alaska Peninsula spreads
rain, changing to snow further inland into the AKPEN, Kodiak
Island and along the Kenai Peninsula into Prince William Sound,
diminishing through Saturday. A well developed low and front bring
more moderate rain and gale force winds into the Western
Aleutians Thursday, and spreads over the Aleutians and Bering as
the low tracks East. Gale force winds push across the Central and
Eastern Aleutians for Friday, diminishing late Saturday as the
gales move into the Western Bering but maintaining gusty winds up
to gale force all the way over to the Gulf by Sunday. With the
associated front closing in on the AKPEN and Kodiak Island, areas
of heavy rain develop along the Pacific side from the Shumagin
Island to the mouth of Prince William Sound by Sunday.

&&

.AVIATION...

PANC...VFR conditions and light winds will prevail. Isolated low
stratus and fog may be visible south of the terminal area,
dissipating through the morning hours.

&&