Storm Warning 194, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
511 AM AKST Thu Dec 12 2024

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

Discussion:

Satellite imagery this morning shows several features over the Gulf.
Two lows were noted lifting northward out of the North Pacific into
the eastern Gulf and onwards towards Southeast Alaska. A smaller
feature is beginning to take shape just east of Kodiak Island.
Lastly, our northern Gulf low is moving westwards over the western
Prince William Sound and the associated front has started to move
inland and north across the coastal mountains. Precipitation has
started to fill in across the southern Kenai Peninsula with more
showery conditions across the northern half and up towards the
western Chugach as midlevels start to cool. Precipitation then
becomes more widespread on the Gulf side of the low resulting more
steady precipitation this morning for Cordova and Valdez. The low
will weaken as it moves towards the Cook Inlet later this morning,
but the trough lingers over the area through mid-morning Friday.

Models still favor the bulk of the heavier, and more steady rainfall
from Cordova, Valdez, and the western Gulf including
Whittier...though Whittier may see periods of a mix of rain and snow
or all snow. The western Kenai Peninsula will continue to see light
precipitation in the form of rain or a mix of rain and snow for
Homer with the potential for a mix closer to Kenai and Soldotna
before changing over to all snow later this morning as the column
cools. Precipitation type and extent for Anchorage up through the
Mat-Su Valley are still a little uncertain. The latest 12Z sounding
shows quiet a bit of dry air in the lower levels, but also shows
that the midlevels are cooling. Anchorage, especially the Hillside,
have greater chance of seeing measurable precipitation today, but
overall amounts are still expected to be minor. Precipitation type
will depend on how quickly the column saturates and the vertical
temperature profile with time. Right now the thinking is that the
Anchorage Bowl up to Eagle River could see sporadic showers this
morning, either rain or a mix. Later this morning and into the
afternoon, the midlevels should be cool enough and wetbulbing down
will result in a changeover to light snow. The probability of
precipitation will decrease as we head into the afternoon/evening.

Looking ahead into the weekend... An upper trough is still on track
to ooze southwards into the Alaska Interior could keep inland
portions of the Susitna Valley and most of the Copper River Basin
showery with snow. And while the longer range models all agree on
bringing this feature down, they have yet to converge on a defined
track and placement of the upper low.

- PP

&&

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

Southwest Alaska continues to quiet down as the trough over the
area slowly shifts northward. The lower Kuskokwim Valley will get
some light snow today through Friday morning, with areas near the
Alaska Range getting around 2-4 inches of snow. Temperatures near
Bristol Bay and the Kuskokwim Delta will hover around the mid 20s
over the next few days, with a more noticeable drop in
temperatures occurring in the lower Kuskokwim Valley. Values in
the valley will be in the 20s today and Friday, but are expected
to drop into the teens and in the single digits for the northern
parts of the valley by late Saturday.

For the central and eastern Bering, expect showery conditions to
continue as the broad low pressure system lingers through most of
the day today. A ridge will move eastward across the Bering late
Thursday, forcing the low towards the mainland and weakening it in
the process. Behind the ridge will be a robust low entering the
western Bering/Aleutians late Thursday, with its front pushing
eastward into the start of the weekend. The front will bring
gale-force southerly winds through Adak and Atka before weakening
as it moves over Unalaska and the Pribilofs. The sting jet
wrapping around the backside of the low will bring storm-force
winds with hurricane-force gusts to the western Aleutians. The
cold air wrapping around the system will return widespread snow
showers to the central and western Bering Sea. Some uncertainty
exists with a different system south of the eastern
Aleutians/Alaska Peninsula on Saturday. It is a very deep system
with hurricane-force winds, but the northward extent of it could
affect southern marines zones of the Alaska Peninsula. The worst
of the winds should remain over the open ocean, but it is
something to keep an eye on.

-BS/MTL

&&

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

Sunday starts with a low south of the Alaska Peninsula and the
Eastern Aleutians. This low will be a bit far from the coast, so
only low-end gale force winds and a bit of precipitation will
impact the coasts. The Southwest mainland will see snowfall with
more of a wintry mix in the Alaska Peninsula. Ridging will be
present in the Central Aleutians. A powerful North Pacific low
moves into the west Bering Sunday morning. This low bottoms out at
around 935 mb to 945 mb depending on which guidance is being
used. This low will bring high end storm force winds and heavy
rains to the western Aleutians as it slowly tracks eastward. The
low will push the previous low and the ridging out of the Bering.
Guidance predicts that this low will stall in the Central Bering
by Tuesday and continue to bring precipitation and winds to the
Bering through the long term forecast. However, there is quite a
bit of uncertainty on where exactly the low will stall and what
locations will receive the greatest wind speeds and
precipitation. Many shortwave troughs pass under the low and
track eastward as it sits in the Central Bering.

Southcentral will be even more uncertain than the west. The term
"uncertainty" will be quite common in this section. Some guidance
tries to set up a low over the Kenai Peninsula, which could bring
snowfall for the Anchorage Bowl and Mat-Su Valleys on Sunday.
Monday and Tuesday have more uncertainties regarding the
orientation of pressure gradients in the Gulf. If they set up
correctly, Southeasterly winds funnel moisture straight into
Kodiak, causing heavy rains. However, it is also uncertain if the
atmospheric river will be favorable for this circumstance. Other
guidance has a ridge setting up which would not allow much
precipitation. Tuesday to Wednesday has a low rising into the
Gulf, but once again, it is uncertain where the low will end up
and when it will get there. Regardless, gale force winds and
moderate to heavy precipitation will accompany the low, wherever
it ends up.

-JAR

&&.AVIATION...

PANC...VFR conditions this morning may see lowering ceilings to
near-MVFR by mid to late morning. Showers are expected to build
over the Eastern Turnagain Arm and high Anchorage Hillside early,
with a chance for some showers to persist over the terminal,
potentially lowering ceilings to MVFR criteria. Showers over the
terminal becomes increasingly unlikely after 18-20Z, and colder
air filtering into the area will potentially shift any remaining
precipitation into snow. Any snowfall over the terminal may reduce
visibility to IFR criteria, however confidence regarding any
snowfall accumulations is low. Winds are expected to shift
southeasterly over the terminal, persisting into the evening.

&&