Gale Warning 19, NWS Anchorage, AK

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

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

Key Messages:

* Winds to continue diminishing tonight as temperatures similarly
  drop overnight for much of Southcentral. 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 increase in ridging is leading to
the diminishing winds in areas of interior Southcentral tonight.
Notable exceptions to this are Thompson Pass and the Valdez area,
which are expected to continue seeing strong and gusty winds
through the weekend.

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. Models have not been
performing well regarding the cold temperatures, and there is a
large spread in model solutions regarding how cold it will get in
areas of Southcentral detached from the coast. Experience suggests
persistent clear skies overnight will produce colder temperatures
than guidance typically suggests, ergo cold low temperatures are
expected to grasp Southcentral this weekend, particularly for
inland areas.

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. While model guidance has all
trended toward bringing this front further north as the Bering
ridge retreats westward, there is still a large divide in how
quickly the front advances northward. Thus, there is a chance for
Kodiak Island to see a period of light rain and snow, particularly
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 continues to be low.

&&

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

Key Messages:

* Persistent 20 to 30 kt winds across the Bering Sea, AKPen, and
  Aleutians through late Friday. Winds increase into the weekend.

* A very cold, arctic airmass moves over Southwest Alaska
  beginning Saturday. The combination of strong winds and cold
  temperatures will produce wind chills between -25 and -35
  degrees by Sunday morning. Some locations could see wind chills
  near -40 degrees.

* There is increasing confidence in the development of extreme
  freezing spray across the northern and eastern Bering Saturday
  evening through Tuesday.

High pressure extends from Interior Alaska across Southwest
Alaska and the Bering Sea, making for continuing relatively quiet
conditions across the region. Generally expecting clear skies,
though bands of mid and upper levels clouds will pass over the
region from time to time as they rotate from Southwest Alaska to
the Bering Sea around the periphery of the ridge.

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
with gusts over 40 knots 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 through the weekend, expect wind chills to drop into
the 30s below zero as Arctic air continues to press southward.

-CQ/TM

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through Thursday)...

A Western Bering upper level ridge continues to move to the
southwest through the period. A longwave trough develops along the
Canadian border and links with an upper level low in the Northern
Pacific. Models are in good agreement in the upper level
evolution through Tuesday, but begin to diverge by Thursday. Cold
air advection continues across the interior and spreads into the
southwest through Thursday. Gusty winds will promote wind chills
between 20 and 40 below across southern Alaska. Heavy freezing
spray expected in Bristol and Kuskokwim Bays, with lesser amounts
over the southern Bering. A North Pacific low will throw moisture
into the Alaskan Peninsula into midweek leading to periods of
locally heavy snow. Moisture ahead of a front in the Gulf of
Alaska will be advected into the south central coast leading to
areas of locally heavy snow from eastern Kenai to the Canadian
border.

KZ/ME

&&

.AVIATION...

PANC...VFR conditions will persist through the TAF period. While a
couple northerly gusts to 20 kts will remain possible this
afternoon and evening, winds are still expected to become light
at generally 10 kts or less by tonight at the latest.

&&