Storm Warning 212, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
832 AM AKST Sun Dec 22 2024

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

Southcentral Alaska's pattern of persistent southeasterly flow
pumping in the warm air will continue through the next few days
with a series of lows moving through the region during that time.
Early this morning, a weak low was tracking over the upper Cook
Inlet region and bringing in some rain and freezing rain to the
Anchorage area. Temperatures around the Anchorage Bowl, even east
Anchorage should warm above freezing by noon. This, and the
precipitation diminishing, will end the Winter Weather Advisory
for Anchorage at noon today. The Western Kenai Peninsula has a
little bit of rain spilling over off the Kenai Mountains with the
eastern Kenai under rain with freezing levels over 2000 ft.
Therefore all precipitation in these areas is expected to be rain
today. The Matanuska Valley is also mostly above freezing with
little precipitation making it over the mountains.

As the day progresses, a larger complex low will move through the
Gulf from southeast to northwest. This low will bring another
shot of rain to the Gulf coast. There may be some freezing rain
that makes it north of Thompson Pass to the southern portion of
the Copper River Basin so the Winter Weather Advisory was retained
through 6 PM this evening. The most likely place for this is
along the Richardson Highway from Tonsina to near Thompson Pass.

Monday looks rather warm again, though maybe not quite as warm as
today across Southcentral. Temperatures are expected to drop a
little more on Tuesday which should start to switch the
precipitation type from rain or freezing rain back to snow for
portions of Southcentral not along the immediate coast.

Due to the nature of these complex lows that develop and propagate
in this southeasterly flow, there remain an unusually large amount
of uncertainty in the forecast through the middle of the week.

&&

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

A low embedded within a broad, complex trough extending across
much of the Bering Sea and North Pacific has moved across the
Alaska Peninsula (AKPen) this morning, now situated north of Cold
Bay. Areas of light mixed precipitation that affected parts of
Bristol Bay and the Kuskokwim Delta yesterday evening and into
the overnight have also since pushed offshore. Some of this
precipitation northwest of the low center has now made it to the
Pribilofs Islands where primarily wet snow is falling.

Looking to the forecast, the last in a series of lows that have
continuously been crossing the outlook area from east to west is
expected to approach the AKPen from the Gulf of Alaska by this
afternoon into tonight. This system will merge with the weakening
low sitting out over the Bering as it opens up into an east-west
oriented surface trough. Models have backed off on the idea that
the new system approaching will ever make it into Southwest, with
the latest consensus depicting the low slowing to a crawl as it
approaches Bristol Bay from tonight into Monday. Still, there
should be enough forcing and lift near the upper shortwave trough
associated with this low to fill precipitation back in over
Bristol Bay as the low reaches Kodiak Island later today. A warm
nose of air above freezing aloft will still be in place initially,
while northerly flow out of the Kuskokwim Valley advects cooler
air back south at the surface. This will once again provide a
favorable setup for freezing rain, with the best chance for
accumulating freezing rain up to a tenth of an inch focused
between Koliganek and Dillingham. The Winter Weather Advisory has
been extended out to Monday morning due to the potential for the
additional round of freezing rain beginning by this afternoon. The
entire column will cool below freezing by Monday afternoon,
allowing any lingering pockets of freezing rain to switch over to
snow.

Taking a broader look and a bit further out into the week ahead,
the underlying pattern will finally begin to shift as a North
Pacific low pushes a strong front into the Aleutian Chain between
Monday and Tuesday. Storm force winds will initially be possible
as the front reaches the western Aleutians on Monday, but the
front should quickly weaken to gale force as it continues to lift
northeast into the far southern Bering. Models have struggled
quite a bit to resolve rapid formation and dissipation of
successive triple-point lows along this front, and there may be
changes to the wind and precipitation forecast for Monday into
Tuesday due to this inherent uncertainty for the location of
these smaller low developments. There is a general consensus for
the main low to eventually shift or redevelop towards the AKPen
by Tuesday night. Strong northeast winds will also continue to
spread across the Bering Sea as a colder air mass begins to spread
south from the Arctic by Tuesday night.

-AS

&&

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

An elongated upper level trough extends from the Arctic through
the Eastern Bering into the North Pacific on Wednesday, with
several low centers rotating through the pattern. This trough will
slip over the Central Mainland into the Gulf of Alaska by the
weekend. A ridge over the Bering trailing the trough moves into
Southwest Alaska by Saturday. A second upper trough moves in from
Kamchatka over the Western Aleutians by Saturday. An upper ridge
over Southeast Alaska moves into the Canadian Provinces through
the end of the week. The ECMWF/GFS/Canadian models handle the the
strengths and tracks of the weather producers through the end of
the forecast period.

Most of the jet support rides across the North Pacific to the
South of the Aleutians and Alaska Peninsula. On the surface, a
series of lows and fronts will track over the Eastern Aleutians
and AKPEN over Kodiak Island into the Gulf before pivoting into
the North Gulf Coast. This will bring repeated rounds of locally
heavy rains to the Southcentral and AKPEN coastal zones and Kodiak
Island. Gusty Easterly winds spread over the Northern Gulf
Wednesday, and diminish Thursday. With cold air seeping across the
Interior from Canada, a band of mixed rain and snow or freezing
precipitation away from the coasts along the Northern edges of the
Precipitation areas, with snow mostly further inland. Gusty
Northeasterly winds just below gale force spread over the Central
and Eastern Bering and across the Aleutians and AKPEN through the
forecast period.

&&

.AVIATION...

PANC...VFR conditions to persist. Light NE'ly sfc winds will be
offset by E'ly flow above 1500' leading to areas of LLWS thru the
TAF period. A passing front will keep rain in the vicinity,
though the morning PANC sounding shows a dry layer from 1000' to
4000', which will keep any rain light. Warmer temps over the
terminal will keep the threat of freezing rain low.

&&