Storm Warning 214, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 PM AKST Fri Dec 27 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Sunday night)...

In the near term, the weather across Southcentral Alaska will
continue being dominated by small features moving through the
flow. There is currently a weak low in the northeastern Gulf
moving westward, bringing the chance of precipitation to the
Cordova tonight. This system is showery in nature, and with little
forcing it is unlikely the Copper River Basin will receive more
than an inch or so of localized precipitation. On and off areas of
fog have been observed from Valdez to Gulkana, and it is likely
for it to return to low lying areas across the Copper River Basin
tonight.

Further east, a trend in clearing skies and sufficient moisture
at the surface tonight are looking favorable for fog across areas
of the Western Kenai Peninsula, along the Knik Arm from Anchorage
to Palmer, and the Susitna Valley. Cold air will continue to
filter down into Southcentral as high pressure builds in over the
interior. The models have trended towards closing off this high
pressure system, giving us to more easterly flow rather than
northerly. This could have an impact on the timing and strength of
outflow/gap winds expected as a result from the cold air
advection and pressure gradient. Thompson Pass and/or any other
locales with transportable snow in these gaps and passes may
experience periods of drifting and blowing snow. Otherwise,
cooler and quiet weather is anticipated for much of the area. By
Monday morning, a strong low from the Aleutians will move into the
Western Gulf, bringing enhanced winds and precipitation to Kodiak
Island.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA AND BERING SEA/ALEUTIANS
(Friday evening through Sunday)...

The proverbial calm before the storm will be winding to a close
as the weekend approaches. The bulk of the weather concerns will
start along the Aleutian Chain and work east through Sunday.
Across the surface map this afternoon, an expansive ridge of high
pressure spans the Bering Sea and Central Aleutians. Deepening
low pressure on the southern tip of the Kamchatka Peninsula is
where attention focuses tonight and into the last weekend of 2024.
In the upper levels, and incredibly strong sub tropical jet (185+
knots) is nosing in from the west and into the northern Pacific.
In the left exit region of this jet is where the aforementioned
Kamchatka low resides. Overnight this low will deepen down into
the low to mid 960's and detach from the support of this jet,
letting it eventually come to it's demise. To the southeast of
this low and along an occluded front will be one of series of
triple point lows progged to develop and spin up along the nose of
the jet and weather front. The first of these triple point lows
has already formed south of Shemya and will lift north across the
western chain late tonight and into tomorrow. Polar orbiting ASCAT
passes are already showing high end gale force winds, and with
the forecast deepening of this low, we're expecting these gales
with storm force winds to impact areas from Atka and west. These
strong southerly winds, coupled with a plume of moisture from deep
in the pacific, will bring back moderate rainfall as this front
slides east along the Aleutians. Snow may briefly fall at the
start, but is expected to quickly transition over to rain and
remain.

By Saturday afternoon and into Sunday, the previously talked about
low will become vertically stacked and detach from any upper
level support. This will allow it to weaken in a nearly stalled
out state over the western Bering. Farther east, it's going to
sound like a rinse and repeat scenario. Another triple point low
will develop south of Unalaska and lift north across the eastern
Bering and AKPEN into Sunday. Model and ensemble guidance has been
really struggling with how this situation will pan out, but are
finally coming into agreement this afternoon. Concerns now shift
from Dutch Harbor and will include Cold Bay, where storm (to
potentially hurricane force) winds will slam into the Peninsula.
This could also cause issues along the Bristol Bay and Y-K Delta
coast leading into the start of the work week.

&&

.LONG TERM FORECAST (Days 4 through 7: Tuesday through Friday)...

There will be some adjustments to the broad upper level trough
extending from the Russian Far East across the Aleutians and
Bering into the Gulf of Alaska through the forecast period. The
jetstream support for the main storm track sags into the Western
and Central North Pacific and Western Bering. The Eastern portions
remain more or less in place and weaken into a broad trough
through Friday. A number of low centers transit through the
pattern. An upper level ridge builds from the Western Canadian
Provinces across most of Mainland Alaska into the Russian Arctic
Coast. This ridge will help spread drier and cooler weather over
much of the Interior and Southern Alaska.

A series of lows and fronts work their way across the Aleutians
and Bering through the week. Locally moderate precipitation
starting as snow, but changing to rain will spread over the
Aleutians and Bering and into Southwest Alaska and the Alaska
Peninsula. Occasional periods of gusty surface winds will
accompany the fronts. A developing low over the North Pacific
Thursday brings periods of gale force winds into the Western
Aleutians Thursday morning, diminishing Friday morning while
extending the gusty wind field over the Aleutians to the AKPEN. In
the East, a low center meanders around the Gulf with areas of
rain across Kodiak Island, Prince William Sound and the rest of
the Southcentral coasts. Areas of more isolated to scattered snow
are expected further inland. Widespread Easterly gusty winds with
patches of gale force gusts near Kodiak Island occur Tuesday
through Wednesday night, diminishing.

&&

.AVIATION...

PANC...VFR conditions will persist through this evening along with
light winds. Ceilings around 4,000 ft to 5,000 ft this evening are
still expected to lower through the evening and nighttime hours to
low VFR or MVFR along with a slight chance of very light snow.
Breaks in this cloud deck may occur overnight into the morning
hours of Saturday. If so, there will be the potential for fog
development from Northern Cook Inlet to Knik Arm. Any fog that
does develop over the waters to the north and west of the terminal
could drift over the terminal by early morning Saturday dropping
visibility to IFR or lower.

&&