Gale Warning 866, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
433 PM AKST Thu Dec 5 2024

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

Key Points:

* Temperatures are expected to dip at or below freezing after
  sunset and tonight. Any water on untreated surfaces will
  refreeze.

* Another round of freezing rain and drizzle is possible after
  midnight tonight through Friday morning.

* Winter Weather Advisory has been extended for Anchorage,
  Matanuska, and Susitna Valley through noon Friday.

* Patchy fog may develop where skies clear along the Kenai
  Peninsula, Anchorage, and the Matanuska and Susitna Valleys
  tonight and Friday night.

Discussion:

Many areas reported freezing rain today across Southcentral.
Temperatures this afternoon rose into mid to upper 30s in many
locations and the Copper River Basin through Valdez was allowed to
expire. However, temperatures will cool again tonight and any
water on untreated surfaces will refreeze. A sliver of clearing
skies on satellite has allowed for fog to develop in portions of
the Kenai Peninsula. Fog is expected to be patchy and brief as the
slot moves north, fog develops elsewhere, and the increasing cloud
cover with the next system improves visibility.

However, the next deepening surface low over the North Pacific
pushes northward into the Gulf for Friday. This low will drive a
front northward bringing gusty gale force winds to the coasts and
usual gap regions as well as another burst of precipitation. This
low will mainly affect Kodiak Island and Prince William Sound as
Anchorage and the Kenai Peninsula will experience downsloping.
This precipitation will be mostly in the form of rainfall as the
warm air mass remains in place. However, yet again, with
temperatures along the lee of the coastal mountains cooling back
to around freezing following today's event, any precipitation that
does spill over the mountains Friday morning would likely fall as
a period of light freezing rain. Freezing rain potential will be
more likely for the Anchorage area, especially south and west
Anchorage. The potential also cannot be ruled out for the
Matanuska Valley as well. This and the temperatures dipping below
freezing tonight has led to the decision of extending the
advisories through noon Friday.

Looking ahead, a shortwave ridge could bring another round of
patchy fog for Saturday, though confidence at this time is low.
Yet another system is scheduled toward the end of the weekend,
reaching Kodiak on Sunday morning. Gale force winds are expected
along the front and ample moisture looks to be associated with
this system. Again, warm southeasterly air looks to advect into
Southcentral. Timing of its passage is a little uncertain still,
though Sunday into Monday is the likely timeframe. Midlevel
temperatures also vary and precipitation type challenges seem
moderately likely. Please stay winter weather prepared and check
for updates to the forecast.

-TM/Rux

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

Though the low remains stationary off of the Kuskokwim Delta
coastline, the main field of moisture has pushed northward and a
bit of dry air has moved in. This has allowed the main threat of
mixed precipitation including freezing rain to subside. Despite
this, there remains a chance for brief showers across the
Southwest mainland through Saturday. As for the Bering, there is a
low over the Shemya region which is allowing for small craft
winds and precipitation in the western Aleutians. This low will
begin to dissipate by Saturday. Back to the mainland, ridging
builds in on Saturday, which will allow for calmer and drier
conditions. This ridging will be brief and is quickly pushed out
Sunday afternoon by a North Pacific low that will lift into the
Bering.

This North Pacific low will send bands of precipitation across
the Southwest. The Bering could see a brief period of mixed
rain/snow before warm air advection occurs and transitions the
precipitation fully to rain. Gale force winds will accompany this
low and will set up on the southern coasts of the Aleutians and
the Alaska Peninsula. On the mainland, another round of freezing
rain and/or snow mixed with freezing rain could occur in Bristol
Bay. This will be short lived as strong downsloping southeasterly
winds will quickly warm the region and transition the
precipitation to rain. The King Salmon area in particular will
see chances for precipitation heavily diminish with the southeast
winds. Iliamna in particular is showing very strong winds of over
70mph+ at 950mb. In the Kuskokwim Delta, mainly snow is expected,
but a small possibility of snow mixed with freezing rain is
possible in the Bethel region. However, this is highly dependent
on how warm temperatures get and how much downsloping the area
receives once the winds turn southeasterly.

A troughy pattern is expected in the future with a few more lows
looming west of the Bering Sea after Monday. These will likely
bring more gusty winds and precipitation in the future.

-JAR

&&

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

An extended, negatively tilted upper trough situates itself
across the Bering Sea and Aleutians, and over the Gulf. This
feature deepens as it moves eastward across western AK. The trough
and embedded shortwaves will support a parade of deep frontal
lows to track just south of the Aleutians. A stout southerly flow
will lead to a short lived warming trend into the region as these
lows progress eastward. The aforementioned trough and surface lows
will have strong forcing to support mixed p-types across Eastern
slopes of the Alaska Range, Eastern Kenai Peninsula and across
Prince William Sound to the Canadian border. Rain (which could be
locally heavy at times) is more likely towards the coast, while
frozen p-types will be felt inland. The other major parameter is
wind, which will be quite gusty to gale force through the period
as model guidance notes tight pressure gradients from the synoptic
setup. Troughing begins to flatten towards the latter part of the
period.

&&.AVIATION...

PANC...VFR conditions prevail this afternoon in between systems.
Clearing skies have allowed some low stratus and fog to
develop across portions of the Cook Inlet, but current thinking is
that this will remain out of PANC. Cloud cover will begin to
spread across the area again this evening into the overnight as
the next trough lifts north. A brief period of light freezing rain
is possible again late tonight into tomorrow morning, but
confidence remains quite low. Should any precip fall, it is likely
to be light and in much shorter duration than today (Thursday).
Afterwards, VFR will then prevail for the remainder of Friday in
wake of the systems. Winds will remain light and out of the north.

&&