Small Craft Advisory 78, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
522 PM AKST Wed Jan 24 2024

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

Most of Southcentral will see a continuation of bone chilling
cold temperatures and clear skies tonight, Thursday and Friday.
The gusty gap winds in Seward and Whittier will persist.

However, there is a major moisture laden storm that is currently
near Hawaii and 3 global models bring this system to Southcentral
Alaska Saturday. This system is juiced and will result in a major
pattern change for much of Southcentral. Two of the 3 global
models bring the moisture fetch into Prince William Sound,
Thompson Pass, Valdez and Cordova. One of the global models
actually has a more westerly track for the plume of moisture which
includes Anchorage. Regardless of which global model solution we
go with Thompson Pass, Valdez and Cordova are going to get
hammered on Saturday and Sunday. Because of the uncertainty for
Anchorage, it is still too early to tell exactly how Anchorage
will be impacted. The situation is actively being monitored and
as new runs of the global models become available the situation
for Anchorage will be re-evaluated.

&&

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

Upper level high pressure is currently over the Western Aleutians
and continuing to slide west as a strong low lingering just south
of the Aleutian Chain weakens through early Friday. Over the
mainland, zonal flow predominates with a shortwave trough south of
the Alaska-Canada border jutting into the northern Gulf of
Alaska. 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.

A weak compact trough leaving the Gulf of Anadyr is dipping south
into the Bering Sea before it stalls and weakens near Nunivak
Island Thursday morning. This will mainly bring 20 kt winds and a
20 percent chance of light snowfall for the marine areas before it
gets reabsorbed into the flow farther west.

An upper level trough will follow closely behind over the
mainland interior dipping into Southwest. This will open the door
to reinvigorate cold air advection and increasing winds Thursday
afternoon to at least the end of this week. Winds may become more
northerly as the trough deepens south and speeds increase to gale
force. With the cold air advection, winds could become especially
gusty through susceptible terrain gaps. Confidence remains low
with regards to precise wind speed and temperature values due to
variations between model runs, however, moderate to high
confidence remains for increasing winds and frigid temperatures by
Friday. Widespread wind chill temperatures over much of Southwest
is likely to dip into the minus 40 to minus 50 degrees Fahrenheit
range. Over the lower Kuskokwim Valley, even colder 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. It could last 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.

rux

&&

.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 winds will persist through the TAF period. Fog and
low stratus will likely continue to erode through the early evening
hours. Fog and low stratus are then likely to return to the
terminal after sunset, at a similar time to yesterday (by 11 pm
AKST). Any fog and low stratus that does develop is expected to
remain through late Thursday morning.

-TM

&&