Gale Warning 23, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
324 PM AKST Sat Jan 27 2024

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

Key Points:

* Winter Storm Watch has been upgraded to a Winter Storm Warning
  for the southern Copper River Basin. Long duration snow and
  periods of heavy snow is expected along the Edgerton Highway and
  Richardson Highway south of Tonsina. Snow amounts of 25 to 50
  inches is possible.

* Winter Storm Watch for northeast Prince William Sound, Valdez
  and Thompson Pass has been upgraded to a Winter Weather
  Advisory. Long duration snow and periods of heavy snow expected
  in both Valdez and Thompson Pass with snow amounts up to 45
  inches possible.

* A Winter Storm Watch has been issued for the Seward Highway,
  from Girdwood to Portage, and Turnagain Pass to Summit Lake for
  persistent snowfall and a period of heavy snow. Snow amounts of
  20 to 30 inches, and 15 to 28 inches respectively is possible.

Discussion:

Models have started to come into better agreement for Gulf low
tracking towards western Prince William Sound over the next few
days, leading to a more active weather pattern for much of
Southcentral. Long duration snow is expected for many areas along
the southern portions of Southcentral. The main areas affected are
around Prince William Sound and the Southern Copper River Basin.
Thus, we have issued two new winter weather products, a Winter
Weather Advisory and a Winter Storm Warning, in effect Sunday
night through Monday night when heaviest snow and highest snow
amounts are likely. Snow will quickly work its way eastward
towards the eastern Kenai Peninsula, and a Winter Weather Watch
has been issued. Cordova is, currently, the only area expected to
warm up enough to transition to rain. The Winter Storm Watch for
Cordova has been canceled and a Special Weather Statement has been
issued to address the new snow totals, 8 to 12 inches, and the
transition to rain.

Extreme freezing spray will continue to be a hazard out of
Kamishak Gap and bays and passes through Shelikof Strait. Heavy
freezing spray will be an issue tonight for Resurrection Bay,
Passage Canal, and the Valdez Narrows.

&&

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

An upper-level trough stretching across the northeastern Bering
Sea and mainland Alaska continues to push high pressure to the
southwest out of the Bering. Frigid air temperatures and clear
skies are currently the name of the game for Southwest Alaska as
the southward digging trough advects an extremely cold Arctic
airmass across the region. With the cold air advection, winds have
become gusty through susceptible terrain gaps, and wind chill
temperatures over much of Southwest are likely to remain in 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. Thus, a Wind Chill Advisory remains in effect
for the Lower Kuskokwim Valley, Kuskokwim Delta, and Bristol Bay
through Sunday morning. Bristol Bay, the eastern Bering, and the
southern marine side of the Alaska Peninsula can consequently
expect to see extreme freezing spray, with vessel ice accretion of
at least 4 cm per hour near the ice edge. Temperatures will
gradually rebound early to midweek next week as an upper-level
ridge builds from the North Pacific.

Further to the west, a compact polar low from Siberia is headed
towards the Pribilof Islands. It is expected to track across the
islands late tonight through early Sunday morning, bringing a
quick round of heavy snow and strong east-northeasterly winds
gusting as high as 35 to 45 mph. Gusty winds combined with heavy
snowfall may reduce visibility to one mile or less at times due to
blowing snow. The worst conditions will be brief, likely only
lasting a few hours around midnight tonight. The system continues
across the eastern Bering Sea and to the eastern Aleutians through
Sunday afternoon, bringing with it wind gusts as high as 60 mph
across the Pribilof coastal waters and eastern Bering waters.
Periods of freezing spray and reduced visibilities will be
possible during the strongest winds. Model discrepancies have
become minor, providing high confidence that this will be a quick
hitting system. A Special Weather Statement and Marine Weather
Statement have been issued for this system.

Moving into Monday, generally active weather continues for the
Bering and Aleutians as upper shortwaves embedded within the
aforementioned trough continue to traverse the region.

&&

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

Looking ahead to the long term, a negatively tilted trough sweeps
east across southern mainland Alaska and the Gulf of Alaska,
exiting to Canada and Southeast Alaska by Thursday night. In its
place, a ridge builds up from the North Pacific ahead of a
complex of lows moving into the western/central Bering Sea as
early as Wednesday. Through the end of the week the low complex
pushes east to encompass the whole Bering Sea, with associated
fronts moving into Southwest Alaska by Saturday as the ridge
slowly shifts east across the Gulf.

Winds out of gaps in the western Gulf peak near storm force mid-
week with robust surface troughing in the Gulf and -20C 850 mb
temperatures driven across the Alaska/Aleutian Range by the
upper-level shortwave trough. With the cold air shifting east,
expect another round of temperatures 10 to 20 degrees below
normal. Light snow showers linger across Southcentral Alaska on
Wednesday beneath the upper trough, but these clear out by
Thursday as northwesterly flow brings in the colder, drier air.

Out west, the complex of lows moving into the Bering Sea bring in
a warmer, more seasonable air mass. The Bering and Aleutians see a
return to active weather and can expect multiple fronts to bring
both rain and snow for the latter half of the week. For the
mainland, chances of precipitation increase Friday into the
weekend as the trough progresses eastward. Friday and Saturday
appear to be the best chance for precipitation in Southwest
Alaska, where precipitation type will likely be snow, though some
potential for rain or some sort of wintry mix cannot be ruled out
as temperatures warm. By Saturday, precipitation may begin to
nudge into the western half of Southcentral to affect the Kenai
Peninsula, Anchorage, and the Mat-Su Valleys, though the details
of this remain unclear at this time.

CQ

&&

.AVIATION...

PANC...VFR conditions and light winds will persist through
tonight. There remains some uncertainty as to the timing of a
system moving in from the east Sunday afternoon through Tuesday.
While clouds are expected to move in Sunday, conditions are
expected to remain VFR through the day. There is a slight chance
for some MVFR ceilings by late afternoon, but it is more likely
for the MVFR or IFR conditions to move in with some snow Sunday
evening.

&&