Gale Warning 102, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
444 PM AKST Thu Jan 25 2024

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

Relatively benign weather will continue through tonight. Areas of
fog may develop in the valleys and low lying areas tonight into
tomorrow morning.

Active weather returns to portions of Southcentral tomorrow.
Primary areas of concern will be the Copper River Basin, eastern
Prince William Sound, and Cordova as a series of low pressure
systems track northwards across the Gulf of Alaska. Longwave
Arctic troughing extends south over much of the western portions
of Southcentral, including the Mat-Su Valleys, Anchorage, the
Kenai Peninsula, and Kodiak Island. The trough looks to be strong
enough to keep the heavy precipitation associated with the Gulf
low(s) from spilling into these regions, however, some light,
localized precipitation is possible. There have been quite a bit
of model inconsistency with these incoming Gulf lows bringing
varying amounts of snowfall to different regions. The most recent
runs are pointing towards a further east track, resulting in a
long duration snowfall with higher amounts along the northern
coast - Cordova, Valdez, Thompson Pass - as well as the Copper
Basin. Three Winter Storm Watches have been issued for heavy snow
and new snow accumulation beginning Friday and lasting through
Sunday night into Monday morning. Eastern Prince William Sound,
including Cordova, could see between 8 and 16 inches of new snow
accumulation, Valdez and Keystone Canyon with 18 to 30 inches
while Thompson Passes could see 28 to 40 inches of new snow. For
the Copper River Basin, the southern portions of the Basin will
see the highest snow amounts, ranging from 18 to 30 inches, and
from Glennallen to Paxon values range from 12 to 24 inches of new
snow. Snow is expected to be heavy and may reduce visibilities at
times.

&&

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

Upper level high pressure is currently over the Western Aleutians
and continues to slide west as a strong low lingering just south
of the Aleutian Chain weakens through early Friday. Over the
mainland, zonal flow predominates through Friday morning. Skies
will remain mostly clear across Southwest into portions of
Southcentral and the eastern Bering sea as cold air remains in
place with offshore flow.

An upper level trough will develop over the mainland interior
dipping into Southwest Friday afternoon. This will open the door
for more cold air advection and increasing winds to the end of
this week. Winds may become more northerly as the trough deepens
southward, and increase up to gale force. With the cold air
advection, winds could become gusty through susceptible terrain
gaps. Confidence remains low with regards to precise wind speed
and temperature values due to variations between model runs,
however, there is moderate to high confidence for frigid
temperatures and higher wind by Friday. Wind chill temperatures
over much of Southwest is likely to dip into the minus 40 to minus
50 degrees Fahrenheit range. In the lower Kuskokwim Valley wind
chill temperatures may reach minus 50 to minus 60 Fahrenheit.
Heavy freezing spray will consequently return toward the end of
the week with ice accretion of at least 4 cm per hour near the ice
edge in the eastern Bering beginning as soon as after midnight
into Friday morning, potentially lasting into next week.

As cold air moves over relatively warmer sea surface temperatures
and winds increase from the north, ocean effect snow showers
could develop across the Bering Sea and becoming more prominent as
yet another embedded trough develops in the north Bering and
reinforces cold air southward for Saturday. Blowing snow and
reduced visibility could become an issue with the snow showers
moving across the Pribilofs, the eastern Aleutians, and the Alaska
Peninsula.

&&

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

The beginning of the weekend will see a trough developing over
central/western Alaska. With the north-south alignment of the
trough, hazardous cold temperatures are possible along the western
portion of the trough, extending into portions of southwest
Alaska. These conditions would persist through the weekend, but
are possible to extend into early next week. With an increasing
pressure gradient forming through the Bering, strong gap winds
across the western Aleutian islands are currently projected during
the weekend.

Through the end of the weekend into early next week, uncertainty
remains on the potential of shortwaves forming in the eastern Gulf
of Alaska, as well as their track. Presently, a series of
shortwaves are expected to provide increased precipitation along
the Alaska Panhandle and will stretch as far west as the eastern
portions of Prince William Sound. Previous model guidance had the
majority of the heavy precipitation primarily along the Alaska
Panhandle, but there are some trends that are starting to suggest
more precipitation closer to Southcentral. Increased model
agreement closer to the event will help with the confidence of
this forecast in the coming days. Additionally, regardless of the
exact location of the trough and shortwaves, gap winds are likely
with this system. The main region of increased gap winds will
extend from the eastern Bering to the western portions of Cook
Inlet and the Alaska Range. Overall, the positioning of the trough
over Alaska in the coming days will play a significant role in
the placement of strong winds and heavy precipitation throughout
the weekend and early next week.

BS

&&

.AVIATION...

PANC...Light northerly winds will continue. Periods of low
visibility (mostly MVFR but may drop to IFR at times) and cloud
ceilings dropping below 300 ft is expected through the overnight
hours with areas of vicinity fog. Conditions should improve
through the morning hours.

&&