Gale Warning 672, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
530 PM AKDT Tue Oct 29 2024

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

Key Messages:

- A Blizzard Warning remains in effect through Wednesday morning
  for Thompson Pass. Strong, gusty winds and snow/blowing snow
  will lead to visibilities falling to under one half mile at
  times.

- A High Wind Warning remains in effect for Kodiak Island for
northwesterly gusts up to 80 mph through 8 PM this evening. Winds
will then steadily decrease through the overnight hours.

- The next storm system will make its way into the Gulf of Alaska
Wednesday night through Thursday. This storm looks much weaker than
the current one, likely bringing only a few inches of snow to
Southcentral on Thursday.

Discussion:

Heavier snowfall has ended across the western Kenai northwards
through the Mat-Su Valley this afternoon as the system slowly inches
off to the east. Satellite imagery shows that the back edge of the
system is quickly eroding as much drier air plunging southwards.
However, low-level cloud cover has been a bit slower to erode and
the northern Kenai up through the Mat-Su Valley may see flurries
and/or some light snow showers move through this afternoon.
Downsloping off the Alaska Range has allowed temperatures to warm to
near 40 degrees in portions of the Susitna Valley, and into the mid
30s for the Anchorage Bowl this afternoon despite the cloud cover.
Expect temperatures to cool overnight as clouds continue to clear
and winds subside by sunrise.

A stout pressure gradient positioned over the AKPen and Kodiak
Island continue to induce strong northwesterly winds this afternoon
with the Kodiak ASOS reporting sustained winds of 30 to 50
mph...gusting up to near 80 mph at times. A High Wind Warning
remains in effect through 8 PM tonight with winds steadily
decreasing overnight as ridging builds in and the gradient shifts
east and weakens.

Water vapor satellite imagery shows that the trough has elongated
and become negatively tilted over the Gulf. This has resulted in
snow lingering longer over the Copper River Basin, but it still on
track to start winding down as the southern end of the trough
pinches off and forms a new low over the eastern Gulf by Wednesday
morning. Light snow may linger over the basin through Wednesday
afternoon as the northern portion of the finally gets pushed east
with upper ridge moving into Southcentral; however, any additional
snowfall tonight through tomorrow for the Copper Basin should be
light. The southern end of the Basin up towards Thompson Pass may
still see several more inches of snow tonight.

With this current system winding down and moving out, we look ahead
to the next system that will approach Southcentral Wednesday night
into Thursday. While Southcentral will see some snow out of it,
models are in good agreement of it moving through fairly quickly
and the bulk of the precipitation falling over the eastern Kenai,
Prince William Sound, and the northern Gulf coastal zones.
However, lack of good cross-barrier flow will result in up to
several inches of snow for the western Kenai and points north.

- PP

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA AND THE BERING
SEA/ALEUTIANS (This afternoon through Friday)...

Currently, a strong low in the Gulf of Alaska is channeling
northwesterly winds through the Alaska Peninsula. This, combined
with a cold air mass is allowing for high-end gale force gap winds
to occur. As the low moves southeast and warmer air moves in, the
winds diminish and end by early Wednesday.

The storm force wind producing front in the western Aleutian
Islands has weakened and is now only producing gale force winds
near Adak. This front will continue to weaken as it presses
eastward and winds will diminish to small craft by the time it
reaches the Alaskan mainland Wednesday afternoon. Though strong
winds will not be much of an issue for the mainland, the large
band of precip associated with the front remains intact and will
move onshore by Wednesday evening. Warm air advection will flow
into Southwest Alaska the same time the front moves in which will
influence precipitation type. Exactly how much warm air advection
the region will receive is uncertain, so confidence is lower
regarding precipitation type. Bristol Bay will see a mix of rain
and snow with northern areas seeing mostly snow. The Kuskokwim
Delta will see mixed precipitation closer to the coast and snow
further inland including the Bethel area. Snow accumulations vary
by region, but range from 2-4 inches in most areas.

The next event is a strong triple point low that will quickly
begin affecting the central Aleutian Islands on Friday. From
there, it will continue to the eastern Aleutian islands and the
Alaska Peninsula. This low will produce storm force winds and
heavy precipitation. There is much uncertainty regarding the track
of the low. Ensembles reveal that it could track through Bristol
Bay or through the Northern Pacific waters south of the Alaska
Peninsula. If the northern track wins out, the winds will have a
much greater impact. We will continue to monitor the track of this
low.

-JR

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

For the extended outlook, a broad upper level low will move over
the Bering Sea with smaller, fast moving shortwaves rounding the
trough as it progresses eastward Saturday through Monday. The
surface low will move into Bristol Bay with associated fronts
progressing through Bristol Bay, Alaskan Peninsula and eventually
out into the Western Gulf of Alaska. Model guidance for the upper
level features varies with the favored Canadian, ECMWF and UK
suggesting the Bristol Bay route and less likely GFS and AI models
favoring a more southward track into the Gulf of Alaska. Either
scenario will bring possible gale force winds and widespread
precipitation across most the upper Aleutians, AKPEN and into the
Western Gulf through Sunday with conditions improving on Monday.
This system will eventually combine energies an approaching North
Pacific system over the Central Aleutians on Tuesday.

&&

.AVIATION...

PANC...Snow has ended and VFR conditions will remain. Occasional
gusty winds (~25kt) remain possible into the overnight hours.
Any gusty winds lingering into the early morning hours will
diminish by mid-morning. Ceilings will continue to improve,
eventually becoming clear by dawn.

&&