Gale Warning 16, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
510 PM AKST Sat Jan 4 2025

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

Some of the coldest temperatures experienced this season,
especially for the Copper River Basin and along the Richardson
Highway, are slowly starting to increase as the first of several
troughs is pushing northward towards the coastline of
Southcentral. Temperatures across most of the Basin are hovering
around 15 to 20 below zero, with feels-like temperatures in the
20s to 30s below zero. Ahead of the first trough passing over the
region, cloud cover has blanketed most of Southcentral and brought
temperatures for most places into the high single digits or low
teens.

Our area of focus begins tonight and will continue well into next
week as a series of lows move northward towards Southcentral. On
one hand, models are in good agreement that a persistent pattern
change will take place over the forecast area. On the other hand,
models still are not clued in on the track and timing of the
systems as they enter into the Gulf. The first wave of
precipitation has made its way into most of the Copper River Basin
Prince William Sound, and eastern Kenai Peninsula, mainly in the
form of snow. Additionally, a Winter Weather Advisory for blowing
snow is in effect until 9AM Sunday for Thompson Pass and Keystone
Canyon. The second weak wave mill move over the Gulf coast Sunday
morning, again spreading snowfall into the Copper River Basin and
coastal mountains throughout the day.

The two lows/waves following the Sunday wave present the biggest
concern, as well as uncertainty. Starting Sunday night and
continuing into Tuesday will be two strong systems that will
produce ample amounts of precipitation for the coastal mountains
and portions of interior Southcentral. Unfortunately, due to warm
air aloft being carried in by both systems, all forms of
precipitation are in play, especially for our lower elevation
locations. Snow levels are expected to rise between 1500-2500 ft
above ground level through the duration of the event as strong
southeasterly winds are expected with both storms increasing the
potential for freezing rain to take place. Due to the intensity of
these systems, multiple feet of snow are likely for locations
above 2500 ft, including Thompson Pass. There are still a lot of
details to iron out given tricky temperature profiles and model
inconsistencies over the next several days, so continue to monitor
for the latest forecast updates for your location.

-BS/PP

&&

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

General north to northeast flow is prevailing across Southwest
Alaska and the Bering with high pressure over Northeast Russia and
the Arctic, and a west-to-east oriented baroclinic zone south of
the Aleutians. Forecast models remain inconsistent, lending to
decreased confidence in the forecast beyond 24 hours. Attention is
focused on an occluded low roughly 400 nm south of Cold Bay. As
this low gradually lifts northward over the next couple of days,
multiple troughs will track across Bristol Bay, with a more
substantial low to push into Southcentral on Monday.

Precipitation will be limited across Southwest Alaska as moisture
is scoured out by the Western Alaska Range. However,
precipitation chances do increase for much of interior Bristol Bay
through Sunday night, especially from Dillingham and Koliganek,
northward. Temperatures across the region will keep precipitation
in the form of light snow, with only an inch or less in
accumulation anticipated at the lower elevations. Further east,
winds coming through the Kamishak Gap will keep temperatures above
freezing, resulting into mostly rain late Sunday into Monday from
Iliamna down into King Salmon.

Further west and across the Aleutian Chain, periods of rain will
be common from the Central Aleutians into the western Aleutians
with the westward progression of a smaller wave of low pressure
rotates across the region and eventually southward back into the
North Pacific by Monday morning. Northerly flow and cooler
temperatures arrive early next week, with any remaining
precipitation to fall as light snow.

Finally, gusty offshore winds moving across the Kuskokwim Delta
and into the Bering will promote freezing spray and heavy spray
near the ice edge, from Mekoryuk, west and south.

BL

&&

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

The start of the forecast period features a strong upper level
low dominating much of the Bering Sea-western mainland Alaska and
a steep ridge of high pressure along the Canadian Coast and
Eastern Alaska. The high pressure ridge will weaken and retreat
eastward slightly along the Gulf of Alaska and Southern Alaska
allowing a very strong North Pacific low and its associated fronts
to travel northward into the Gulf and into the Alaskan Peninsula
Thursday and into Friday before being absorbed by the long wave
trough of low pressure over the Baring Sea. This pattern will
bring unseasonable warmer temperatures and mixed precipitation
along the coastlines near the surface and has the real potential
for heavy snow accumulations in the higher elevations.

The upper level low will gradually retreat back into Eastern
Siberia and the Chukchi Sea as the Ridge of high pressure
reasserts its dominance Friday and into Saturday. This will
flatten out the southern portion of the long wave trough allowing
several compact surface lows and their associated fronts to
transit along the Aleutians and coastal southern Alaska.

Confidence in the model guidance is moderate with a slight bias
between the GFS and European solutions through Thursday. The
European and Canadian better handle the synoptic features Friday
and into Saturday.

DD

&&

.AVIATION...

PANC...Mainly VFR conditions will persist through the TAF
period, though there could be a brief time of MVFR if some snow
showers are able to develop and move through late this evening
into the overnight hours. Other than that, VFR will be the case.
Northerly winds with an occasional gust up to 20 knots should also
remain through most of the day on Sunday. There is potential for
low level wind shear to develop late Sunday afternoon and beyond
as winds aloft strengthen from the southeast and surface winds
remain northerly.

&&