Gale Warning 20, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
445 PM AKST Sun Jan 5 2025

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

Discussion:

Today is the start to more complicated forecast period...with strong
winds, a variety of precipitation types across Southcentral, periods
of moderate to heavy rain for Gulf coastal areas, and heavy snow
anticipated for higher elevations, including Thompson Pass.

Over the past 24 hrs, the first of a series of surface fronts and
upper-level shortwaves has pushed inland and continues to trek
into interior Alaska. Temperatures have warmed a bit in response to
this initial wave, especially for locations that saw an increase
in easterly winds along the immediate coast. A wintry mix of
showers persist behind the trough and in advance of the next
surface low and front pushing into the northern Gulf this evening.

The next front reaches the coast early Monday morning with the 980
mb parent low moving over the Barren Islands. These will bring an
additional push of warmer air on modest southerly flow, and
widespread precipitation to the coastal regions. Lower elevations
along the Gulf that were seeing a mix of precipitation today
should see a rapid changeover to rain (with the exception of
Valdez) as easterly winds again quickly increase. The easterly
Turnagain Arm winds will also likely bend into Anchorage for a
time early Monday morning, allowing temperatures to brief climb
above freezing. Temperatures elsewhere along northern Cook Inlet
will also hold steady around freezing for Monday, meaning any
precipitation spilling over the coastal mountains would fall as
freezing rain. The strong southeasterly flow aloft, however,
should keep any precipitation falling from Kenai to the Susitna
Valley very light.

The more challenging precipitation type forecast will be from
Valdez north into the southern half of the Copper River Basin.
Warmer air will again push inland in the wake of Monday's front.
However, just how much cold air currently over places like Valdez
scours out, remains to be seen. Prolonged snow could fall through
much of Monday before temperatures finally push into the mid 30s
and precipitation changes to rain. A foot or so of snow could fall
before any changeover to rain. Farther inland, similar amounts
could fall through Monday evening as temperatures stay slightly
cooler. However, a wintry mix of snow and freezing rain could fall
along the Richardson and Edgerton Highways in the southern Copper
River Basin.

Yet another, and more powerful storm system, then moves into the
Gulf directly on the heels of the first. This system will likely
have hurricane force winds along its front from Kayak Island to
Hitchinbrook Entrance. Strong wind gusts of up to 100 mph are not
out of the question for Portage and Eastern Turnagain Arm as this
low reaches peak intensity as it crosses the Kenai Peninsula and
into Cook Inlet. Winds to 75 mph will also be possible for the
Anchorage Hillside and the Matanuska Valley as the low enters
northern Cook Inlet. Winds could gusts as high as 60 mph along the
western Kenai Peninsula coast. Winds could also approach 75 mph
for Cordova if the front pushes far enough north.

Precipitation will also begin to spill over the coastal mountains
and fill in across Cook Inlet and the Mat-Su Valleys by Monday
afternoon as the low advances and a strong upper-level wave moves
overhead in tandem with a strong jet streak. Again, any
precipitation for these areas could fall as freezing rain with
temperatures near freezing. Even with temperatures slightly above
freezing, the antecedent cold airmass has allowed ground
temperatures to fall below freezing. Thus, any rain could still
freeze on surfaces.

The low then lifts north on Tuesday, with strong southerly winds
in its wake as pressure rises quickly behind the low. Expect
gusty winds for most locations with widespread gusts of 35 to 50
mph for valley locations.

- TM

&&

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

A trough of low pressure pushed across Southwest Alaska on Sunday
with periods of snow observed at Dillingham and Iliamna. Radar
shows remnants of this precipitation shifting northwestward toward
the Kuskokwim Mountains, which should should filter out any
remaining precipitation en route to the Kuskokwim Delta later
tonight.

A look at the bigger picture shows the continued presence of an
occluded low immediately south of False Pass. This low is
promoting southeasterly flow into the ALaska Peninsula with near
uniform temperatures hovering at 40 degrees from False Pass up
into Port Heiden. Attention is turned to a shortwave trough
lifting northward into the Gulf of Alaska currently, which will
push into Southwest Alaska through Monday morning. This wave will
set off a period of off and on snow showers for interior Bristol
Bay and portions of the Lower Kuskokwim Valley, beginning later
tonight and lingering into Tuesday. Temperatures at the surface
are expected to remain at or below freezing for all areas with an
area extending from Dillingham to New Stuyahok to Koliganek to see
anywhere from a dusting up to 2 inches of snow through early
Monday morning. Easterly winds along the coast, especially into
Dillingham, could see a brief period of light freezing rain this
evening, though this should be short-lived with minimal
accumulations.

A second and stronger area of low pressure is forecast to lift
northward along the Western Alaska Range late Monday through
Tuesday. Precipitation will be more widespread, extending across
much of Bristol Bay into the Lower Kuskokwim Valley. Snow
accumulations of 2 to 4 inches will be common with locally higher
amounts up to 6 inches possible. A sharp cutoff in snow
accumulations will exist along and south of King Salmon, as well
as along and west of Togiak. Still, a dusting to up to an inch of
snow may fall across these areas as well through the morning hours
on Tuesday.

Lastly, a cold airmass remains over the western and northern
Bering where gusty northeasterly winds will continue from Saint
Lawrence Island down into the offshore zone of 411.Gusts of 35 to
as high as 50 knots will be possible within this region along with
seas of 15 to 20 feet. Further east, the threat of heavy freezing
spray will continue along the ice edge from east of Saint Matthew
Island down to immediately south of Nunivak Island.

BL

&&

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

A very active weather pattern will continue for much of southern
Alaska through the end of the week and into next weekend. The
longwave pattern 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.

&&

.AVIATION...

PANC...VFR conditions with a north wind wind prevail through the
first half of the TAF period. Snow will generally remain out of
ANC, though can't completely rule out a few snowflakes. A brief
period of gusty southeast winds out of the Turnagain Arm is
likely early tomorrow morning before winds return to northerly in
response to a strong low moving into the Gulf. Low-level windshear
looks to persist with the strengthening southeast winds aloft
with the exception of the period in which surface winds are out of
the southeast. There is a chance for freezing rain Monday
afternoon and evening, but it is very possible that the cross-
barrier flow over the mountains will be enough to downslope out
the precipitation.

&&