Gale Warning 928, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
508 AM AKST Wed Dec 11 2024

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

Discussion:

A front, extending from a low moving into the eastern Bering this
morning, is slowly lifting northwards across the AKPen and
western Gulf. Per early morning satellite imagery, the front has
reached the southern end of Kodiak Island and will continue push
north throughout the day today. The upper-level low associated
with this system has merged with another low out in the central
Bering Sea and will deepen slightly before it gets shoved towards
Southwest Alaska later this week as ridging builds over the
Aleutians. Mid to long-range models appear to be in general
agreement that the southern end of the low gets pinched off and
slides towards the Kenai Peninsula and northern Gulf by late
Friday morning. This is an important feature to keep an eye on as
well as its evolution since it will bring colder midlevel
temperatures back into Southcentral...which could bring a quick
change of precipitation type from the rain and freezing rain
(that we have seen the past week) back to mostly snow.

For today through tomorrow...steady rainfall will end over Kodiak
with just the potential for some lingering scattered showers by the
afternoon and evening. Steady rainfall will continue for coastal
locations along the Gulf and Prince William Sound. Seward will see
rainfall amounts of a half inch up to an inch, but easterly flow
will limit overall amounts from Seward up towards Moose Pass. The
western side of Prince William Sound will see the greatest
precipitation amounts with the potential for Whittier to see
several inches of rainfall over the next few days. Higher
elevations will see a mix of rain and snow to all snow as snow
levels are sitting at 2000-2500 ft, though they will decrease to
about 1500 ft by Thursday morning. Heavier precipitation will wind
down along the Gulf coast and Prince William Sound areas
Thursday, but as the upper low moves in, may see some unsettled
conditions Thursday and Friday. Have seen some sprinkles and/or
light showers spill over the mountains and into the Anchorage Bowl
this morning. We should see enough downsloping that any spill
over will be limited today with not much, if any, precipitation
anticipated for much of the western Kenai, Anchorage/Eagle River,
and Palmer areas. However, as the aforementioned front lifts
inland early tomorrow morning and surface low develops over Cook
Inlet, will see light precipitation spread up Cook Inlet towards
the Mat-Su Valley. Precipitation types could be interesting, but
the column looks to potentially cool enough that we could see a
mix of rain and snow to start before changing over to light snow.
Regardless, precipitation looks to be light with little
accumulation is expected.

- PP

&&

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

A large low pressure complex in the eastern Bering is slowly
losing its intensity as it continues to get stretched towards the
north and west. Gusty southeasterly winds and unseasonably warmer
temperatures will slowly taper off throughout the day today
before shutting down Wednesday night as a front moves over
Southwest. The overall wind flow will shift to a westerly
direction as cold air that is currently over the western and
central Bering swings around the southern parts of the broad low
pressure system. This flow of cold air will help drop temperatures
back down below freezing, resulting in values hovering in the mid
to upper 20s for most parts of interior Southwest Thursday and
Friday.

From a precipitation standpoint, southeasterly-directed upslope
flow will continue today before the front moves inland. As the
front passes over, light snow over interior Southwest will be
possible through at least midday Thursday. There is the potential
for a deformation band to form over the far northeastern portions
of Southwest Thursday afternoon that could enhance precipitation
totals, however there is not enough confidence in the current
model guidance to make that a definitive setup at this point in
time.

For the Bering, expect showery conditions to the west and south
of the center of the low pressure system as the previously
mentioned cold air will be conducive in producing snow showers
over much of the Bering. A weak ridge will move over the Bering
late Thursday and force the low eastward towards Southwest.
Behind the ridge will be a developing North Pacific low that will
enter the western Bering and Aleutians Thursday evening. Its front
will push to the north and east through the end of the short-term
forecast period, producing gale force winds and moderate to heavy
precipitation as it makes its way into the eastern Bering and
Aleutians by the start of the weekend. The main area of concern
will be near the low center as it continues to deepen Thursday
night-Friday, forming a core of storm force winds to the south of
the low over the far southwestern portions of the forecast area.

-BS

&&

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

The long term forecast begins with an ridge over Southwest
Alaska. This ridge allows for calm and mostly clear conditions. In
the Western Aleutians, a low near Kamchatka will allow for Gale
force winds around Shemya. This low will retrograde northwest on
Sunday as a strong North Pacific low quickly pushes in from the
southwest. The ridge will quickly move out eastward as this low
pushes east. Active weather will begin to impact the Southwest. A
couple of small lows will pass east and will trigger gusty winds
and precipitation for the Bering and into the SW mainland through
the period as the main low stalls in the central Bering. Gusts
through bays and passes will be stronger. There is some
uncertainty in how far the precipitation will extend into the
mainland and for how long. There is more uncertainty regarding
precipitation type. The GFS has a large amount of cold air
advection enter from the northeast whereas the Canadian-NH and the
ECMWF models do not. If colder air makes its way down, more
snowfall is expected.

For Southcentral, an upper level low will allow for higher
chances of precipitation especially for coastal regions.
Temperatures will be generally below freezing and if any moisture
makes it inland, snowfall is expected. Models are showing that
there is a chance that the Anchorage Bowl may see a burst of
snowfall chances on Sunday through Monday. As the aforementioned
low in the West approaches by the end of the period, gusty, gale
force winds will begin to impact the waters around Kodiak Island
including Kamishak Bay. Looking ahead shows that Kodiak Island may
receive significant rainfall as the atmospheric river flows
directly into the island.

-JAR

&&.AVIATION...

PANC...A series of fronts will lift northward across the flow and
onshore along the north Gulf coast. Persistent easterly flow
across the Kenai and Chugach Mountains will maintain dry conditions
with VFR ceilings for the terminal. Meanwhile, light northerly
winds will persist at the surface. During periods of stronger
easterly flow aloft, there could be some low level wind shear.
The most likely time period for wind shear will be between 12Z
and 18Z Wednesday.

&&