Heavy Freezing Spray Warning 21, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
455 AM AKST Fri Jan 26 2024

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

An active weather pattern is about to get underway for southcentral
Alaska. Upper-level troughing across Alaska is beginning to amplify,
with the mean trough axis extending across the western portion of
the state. Meanwhile, a low across the northern Pacific will begin
to pivot northward towards the Gulf of Alaska. As very cold air
spills out of SW Alaska and into the Gulf of Alaska, an intensifying
frontal/baroclinic zone will set up across the Gulf of Alaska. This
frontal orientation along with a deepening and slow-moving longwave
mean trough axis centered across the western side of the state will
set up prolonged westerly flow and a pattern for several storms
affecting the eastern portion of mainland Alaska.

For today, can't rule out some light snow for either the Copper
River Basin and Prince William Sound as models continue to suggest
saturating dendritic growth zone (in the low-levels thanks to the
pre-existing cold air) coincident with a weak trough axis moving
through. The main show begins tonight as southerly flow deepens in
the central/eastern Gulf thanks to the amplifying pattern. Upper-
level divergence underneath the naturally divergence region of the
right-entrance region of a supergeostrophic jet streak, strong warm
air advection, and plenty of moisture advection with a southerly
fetch deep into the North Pacific will combine to create a
widespread and fairly substantial precipitation. Confidence is
highest that the most precip (/snow) will occur along and east of
the Richardson Highway from Valdez northward through Glennallen
and Paxson. Several feet of snow is becoming likely for Thompson
Pass area, with several inches elsewhere along the highway.

Latest model trends show precipitation shifting a bit farther to the
east. This would yield a little bit less snow for Valdez northward
along the Richardson Highway for the first round, at least until the
next stronger wave moves through Sunday into Monday. 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.

Perhaps the bigger story for Anchorage and much of Alaska is the
persistent cold weather that is likely to get even colder. Lows
below 0 (and largely below -10) are likely to continue for most
areas outside of the immediate coast for the next several days.

Brown

&&

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

Influence from a strong ridge continues to bring clear conditions
to Southwest Alaska through the end of this week into the weekend.
Clear conditions across, in addition to a northerly push of gusty
cold winds from Interior Alaska, will make for extremely cold
temperatures with wind chill dropping down to 40 below zero by
tonight. An upper level trough developing over the mainland
interior dipping into Southwest this afternoon will serve as the
catalyst, driving the cold air into our area. 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. 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 over Bristol Bay, the Eastern Bering and the
Southern marine side of the Alaska Peninsula will consequently
will see ice accretion of at least 4 cm per hour near the ice
edge in the eastern Bering beginning as soon as early this
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 may become an issue with the snow showers
moving across the Pribilofs, the eastern Aleutians, and the Alaska
Peninsula depending on the low track. However, confidence is still
low on where this low will track, and how deep/intense it will
become on its way to our area. We will continue to monitor this
potential system and hone in our forecast to reflect the latest
expectations.

&&

.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... VFR conditions expected to prevail through the evening under
near calm and variable winds. Vicinity fog to remain around Cook
Inlet and Turnagain Arm through today with the return of MVFR cigs
by 12z tomorrow.

&&