Gale Warning 18, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
446 AM AKST Thu Jan 18 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Saturday night)...

Key Messages:

* Diminishing winds and falling temperatures across Southcentral
  today. Gap winds will linger into the weekend, strongest in the
  Valdez area.

* Continued dry and seasonably cold conditions for most of the
  region through Saturday. A chance of rain and snow returns to
  Kodiak Island Friday night-Saturday and to the north Gulf coast
  Saturday night-Sunday.

A strong blocking ridge is centered over the eastern Bering Sea
with a ridge axis extending east across the heart of mainland
Alaska. The ridge axis is rotating southward overhead of
Southcentral, with a low and trough over the Gulf exiting
southward into the Pacific. The increased ridging will bring an
end to the strong flow (at all levels) currently in place over
Southcentral. As a result, expect winds to diminish across the
region. Gap winds through the mountains will linger as some
pressure gradient remains between the surface high over mainland
Alaska and the deepening surface low in the northeast Pacific.

The ridge will retrograde westward across the Bering Sea through
Saturday, opening the way for an Arctic trough to drop southward
across mainland Alaska Friday night through Saturday night. This
will bring a reinforcing shot of cold air into Southcentral Friday
night through Saturday, leading to an uptick in winds. However,
steering flow around the Bering Sea ridge combined with the
presence of the low in the north Pacific will take the trough and
cold air advection southwestward across southern Alaska to the
Bering Sea. As a result, this does not look like a "big" wind
event for the region, though most locations will see some gusty
winds. The airmass does look colder than the current one in place,
so expect a general downward trend in temperatures and wind chill
readings as we head through the weekend.

Meanwhile, an occluded front extending from the low in the
Pacific will track northward into the Gulf and toward Kodiak
Island Friday through Friday night. Model guidance has all trended
toward bringing this front further north as the Bering ridge
retreats westward. Thus, it looks more likely for Kodiak Island
to see a period of light rain and snow, especially for Kodiak
City and the Gulf side of the island. The digging trough over
the mainland could eventually interact with this front and bring
a return to precipitation to the north Gulf coast/Prince William
Sound/eastern Kenai Peninsula as early as Saturday night. However,
confidence in the location of key features at this point in time
is low.

&&

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

High pressure extends from Interior Alaska across Southwest Alaska
and the Bering Sea, making for continuing relatively quiet
conditions across the region. Fog will generally not be
favored over the next few days, even as subsidence under the
upper-level anticyclone leads to a strengthening inversion, since
the low-level atmosphere will remain dry and mixed by the
northerly winds. Generally expecting clear skies, though a deck of
altostratus clouds will make for overcast skies as they rotate
into Southwest Alaska over top of the ridge this morning.

High pressure will keep a North Pacific low far to the south of
the area through Saturday night, though its front will make its
way into the waters south of the Alaska Peninsula Friday night
through Saturday, bringing light rain. The static pattern will
continue to support 20 to 30 knot east to northeasterly winds
along the Alaska Peninsula and Aleutian Islands through Friday
night.

For Saturday, a blast of Arctic air begins to dip across
Southwest Alaska and the eastern Bering Sea, leading to falling
temperatures and increasing winds to gale force for the eastern
Bering marine areas. This will allow for the onset of heavy and
extreme freezing spray from Bristol Bay to St Matthew Island,
which is likely to last through Tuesday. With falling temperatures
and strengthening winds, wind chills over portions of Southwest
Alaska begin to dip into the 20s below zero by Saturday night.
Continuing into the weekend, expect wind chills to drop into the
30s below zero as Arctic air continues to press southward.

CQ

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

The Western Bering upper level ridge continues its track into the
North Pacific through the period. A portion of the ridge
amplifies briefly as it moves over Western Alaska through
Wednesday. An upper level low tracks across the Arctic to the
Northwest Alaska Coast and adds support to a developing longwave
splitting Interior Alaska down to the Gulf before curving
Southwestward into the North Pacific. Models are in good
agreement, but diverge somewhat towards the end of the period. The
biggest weather influence through midweek will be the advection
of Bora-like colder temperatures and locally strong gusty winds
spreading across the interior to the Southwest and Southcentral
areas. A low in the Gulf for Monday will help pump moisture over
the coastal Southcentral zones from the Eastern Kenai to the
Canadian Border, but not advect very far inland through Tuesday.

Kutz

&&

.AVIATION...

PANC...VFR conditions will persist through the TAF period. Northerly
winds will continue to diminish this morning as pressure
gradients relax. Later this morning and through the rest of the
TAF period, winds are expected to be light at generally 10 kts or
less.

&&