Gale Warning 954, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
502 AM AKST Fri Dec 20 2024

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

The trailing shortwave from yesterday's gulf low is currently
pushing through the area, bringing a brief period of steadier
precipitation to the Prince William Sound. This light rain and
mountain snow will taper off this morning in the lull between
storms. For today, expect similar conditions to yesterday, though
slightly warmer as increasingly warm air moves into the region.
The next system will first impact Kodiak Island with gusty
northeasterly winds, picking up this evening, followed by rain.
The leading shortwave and surface front will then reach the Sound
around midnight tonight, beginning a period of light to moderate
precipitation along the Gulf Coast, particularly the eastern Kenai
Peninsula. With the low track well to our south, ample amounts of
warm air have been able to move east of the storm, which will
raise snow levels to 2000 to 2500 ft. For the Sound, expect nearly
continuous light to moderate, and occasionally heavy, rain
through the weekend as multiple systems take a similar track from
the North Pacific to near Kodiak Island.

For inland areas the main forecast question is surface temperature
and precipitation type. The 12Z Anchorage sounding is now firmly
into the freezing rain profile, and will likely remain this way
for the foreseeable future. Generally speaking, the upcoming
system will be mostly downsloped, however there will be multiple
periods where there is strong enough upper level dynamics and
enough moisture that rain and/or freezing rain is likely to fall
in the lee of the mountains for areas like Anchorage, the western
Kenai north of Kasilof and the Mat Valley. Currently, this looks
most likely late Saturday night. Temperatures will slowly warm
through the day on Saturday, reaching highs between 29 and 36
degrees for the aforementioned areas. Regardless of the surface
temperature, area roadways that are currently snow covered or have
surface temperatures below freezing are likely to get icy. This
doesn't look like a cold enough setup for true freezing rain that
will accumulate on surfaces like power lines, but area roadways
are likely to become slick (or even more slick than they already
are if we're being honest...). There are still some uncertainties
to work out for Sunday and Monday, but really it looks like more
of the same, coastal rain and chances for rain and freezing rain
for the Cook Inlet areas and Mat Valley. The Interior of
Southcentral should remain dry.

-CJ

&&

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

The underlying pattern that has already been in place for the past
several days is poised to continue well into the weekend. Several
lows will continue to parade from east to west from the Gulf into
the eastern Bering Sea through early next week, each carried by
easterly flow situated on the northern side of a sprawling,
complex upper level trough stretching across much of the North
Pacific and Bering region. One of these lows is now moving
offshore from the AKPen (Alaska Peninsula) this morning and
westward into the Bering Sea. A few light showers are clipping the
northern side of Bristol Bay on the northern periphery of this
circulation, but otherwise dry and cool conditions are in place
across most of Southwest north of the low. This current system
will weaken as it approaches the Pribilofs later this evening, but
could still drop a quick inch of wet snow before continuing
northwest and effectively shearing apart late tonight.

Attention will then shift to the next low in the continued east-
west low track, which will be a much larger and stronger system
moving south of Kodiak Island by early Saturday. North to
northeast winds will quickly pick up across the AKPen and much of
Southwest, with gales picking up ahead of the low both near
Bristol Bay and to the south of the AKPen throughout the day
Saturday as the low marches west. Precipitation will overspread
portions of Bristol Bay as well as the AKPen and eastern Aleutians
as the low begins to slow down and nearly stall out close to the
Shumagin Islands by Saturday evening. However, strong cross-
barrier flow developing across the Alaska/Aleutian Ranges will
limit how much rain/snow can reach the surface across the Lower
Kuskokwim Valley and Bristol Bay through Sunday morning. Better
chances for precipitation will be focused across northern Bristol
Bay near the Kilbucks, including Dillingham and Togiak. Quite a
bit of warmer air aloft will be transported in from the east as
the low approaches, but cold air in place over valleys with
persistent northerly winds at the surface could yield a profile
supportive of sleet and freezing rain, most likely along an axis
from Koliganek to Dillingham Saturday evening. Confidence for
seeing any measurable freezing rain is still low, but is
beginning to increase.

Forecast details begin to fall apart late Sunday into early
Monday as yet another low with a more uncertain track begins to
pinwheel up from the Pacific into Kodiak Island and the Alaska
Peninsula from the southeast. Despite the track spread, this low
does not look like it will be as intense as the previous in the
series, and may even begin to merge with the prior system still
drifting over the eastern Bering by Sunday night. Out along the
Aleutians, more benign conditions will finally turn more inclement
as a deep North Pacific low pushes a strong front into the
Aleutian Chain by late Sunday night.

-AS

&&

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

The long term forecast begins with a low in the Gulf centered
near Kodiak Island. This low will allow for a Gale or possibly a
Storm Force barrier jet to form along the Southcentral coastline.
Gusty winds could even extend into the Barren Islands, and
Shelikof Strait regions. This will all depend on the exact
location and strength of the low which is still uncertain at this
time. As for the West, A col forms over the central Aleutians near
Adak with a deep low to the west. The low will allow for storm
force winds and precipitation in the Shemya region. As the low
travels east, gale force winds will affect the Bering as well as
gap winds Alaska Peninsula near Cold Bay on Tuesday.

Back to the Gulf for Wednesday has a low pushing in from the
Southwest. There is quite a bit of uncertainty regarding its
track, but gale force winds and precipitation are expected to
accompany the low. Upslope flow along the Southcentral coast and
mountainous regions will likely trigger heavier precipitation, but
areas more inland including the Anchorage Bowl will likely stay
on the dry side due to downsloping. A barrier jet may form with
the passage of the low, but like before, this will depend on the
strength and track it decides to take, which is uncertain at this
time. Winds will die down by Thursday as the low dissipates as it
moves inland. As these winds calm down, downsloping will end and
precipitation will finally be able to make it into the Anchorage
Bowl, but exact QPF is uncertain. In the West for Wednesday, the
low will open into an upper level trough and will funnel cold air
from the north. This will allow gale force winds to linger in the
waters west of the Pribilofs and for widespread light snowfall to
occur across the central Bering and into the Kuskokwim Delta
coast. Thursday has cold air advection continuing to filter down
and the 0F line will pass the Aleutian islands, allowing for
widespread but light snowfall. Also, A low will arrive from the
southeast, which has some implications, but it's track is still
too uncertain to make any hard predictions.

-JAR

&&

.AVIATION...

PANC...VFR conditions and northerly winds will persist.
Southeasterly winds to around 25 kt aloft will lead to weak wind
shear through the afternoon.

An approaching front will bring another surge of easterly to
southeasterly 20 kt winds aloft beginning early Saturday morning.
Weaker downsloping with Saturday's storm could bring the potential
for freezing rain as early as 12Z Saturday, with precipitation
forecast to change over to rain around 00Z Saturday as surface
temperatures warm up.

&&

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
327 PM AKST Fri Dec 20 2024

AKZ102-112-121-211500-
Anchorage-Matanuska Valley-Western Kenai Peninsula-
Including the cities of Anchorage, Eagle River, Indian, Eklutna,
Palmer, Wasilla, Sutton, Chickaloon, Kenai, Soldotna, Homer,
and Cooper Landing
327 PM AKST Fri Dec 20 2024

...PERIODS OF RAIN AND FREEZING RAIN THIS WEEKEND...

Multiple storms will move into the Gulf over the weekend, sending
a series of fronts into the coast. Periods of light rain and
freezing rain are expected Saturday through Monday, with the most
likely time for precipitation being Saturday night into Sunday
morning. Currently the most likely areas to receive rain or
freezing rain are: near sea level locations in Anchorage,
particularly east Anchorage, the Western Kenai Peninsula east of
Soldotna, and the Mat Valley near Palmer. Of the above areas, the
Mat Valley is the least likely to get precipitation, but any
falling will likely be in the form of rain.

Given the somewhat warm surface temperatures of 29 to 36 degrees,
for now, it's unlikely that rain would freeze onto surfaces like
power lines and trees, but rain falling onto snow covered and/or
frozen roadways will likely create icy surfaces. Please use
caution if you will be traveling this weekend, and stay tuned to
forecast updates.