Gale Warning 88, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 AM AKST Fri Jan 19 2024

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

Key Messages:

* Dry and cold conditions persist across most of the region
  through the weekend. Temperatures will trend lower over the next
  few days.

* A reinforcing shot of cold air will move into Southcentral from
  the Alaska Interior Saturday through Saturday night. This will
  lead to strengthening winds, especially along the Alaska Range,
  the northern Susitna Valley, and the Matanuska Valley.

A strong closed upper level ridge is slowly tracking westward over
the Bering Sea. A ridge axis extends eastward across southern
Alaska and is moving southward and weakening as a short-wave
trough digs out of the Arctic into northeastern Alaska and a
short-wave lifts northward out of the Pacific into the Gulf.
Warming under the ridge axis along with weakening of the flow at
all levels has allowed winds to diminish across much of
Southcentral and the Gulf coastal waters. Localized gap winds,
driven by pressure and thermal gradients along the mountains,
persist. There are some stark temperature differences between
locations with wind (generally in the 20s) and locations with no
wind (single digits below zero to single digits above zero).

The Arctic trough will reach Southcentral Saturday, bringing
colder air than with the trough that moved through a couple days
ago. However, with the Bering ridge continuing to retrograde
westward, the trough axis will stall near the Alaska Range and
proceed to dig southwestward across Southwest Alaska and into the
Bering Sea. As a result, Arctic air will advect into
Southcentral, but will not continue out into the Gulf. There will
still be an uptick in winds along coastal gaps, but the more
significant winds will be inland along the south side of the
Alaska Range into the northern Susitna Valley, as well as through
the Matanuska Valley. With 850 mb temperatures dropping to roughly
-14 to -24 degrees Celsius, surface temperatures still steadily
fall - even where the wind is blowing. By Sunday night/early
Monday expect much of Southcentral to experience sub-zero
temperatures (degrees Fahrenheit).

Meanwhile, an occluded front will track north from a deep low in
the northeast Pacific, bringing light rain and snow to portions of
Kodiak Island Saturday and persisting through Sunday. Models
continue to struggle with the ultimate fate of the trough sitting
over mainland Alaska. There is potential for it to interact with
some of the moisture in the Gulf and bring precipitation onshore
of Southcentral Sunday. Or it could elongate and weaken in place
with Southcentral remaining dry. If precipitation does push
onshore it will be in the form of snow and there will be a threat
of blowing snow as the gap winds will still be blowing.

&&

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

Only minor changes to the short term forecast at this time,
please see Key Messages below:

Key Messages:

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

* A very cold, arctic airmass moves over Southwest Alaska
  beginning tomorrow. The combination of strong winds and cold
  temperatures will produce wind chills between -25 and -35
  degrees with isolated locations in the Lower Kuskokwim Valley
  could see wind chills near -40 degrees by Sunday Morning.

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

Currently, a high pressure extends from Interior Alaska across
Southwest Alaska and into the Bering Sea, continuing the trend of
relatively quiet conditions across the region for the last week.
This high pressure will keep a north Pacific low to the south of
the Aleutian Chain through tomorrow night. This low and it's
attendant front will bring a slight chance of rain for the AKPen
and Eastern Aleutians through tonight into Saturday. In addition,
with higher pressure over the interior and lower pressure in the
northern pacific, this pattern will continue to support 20 to 30
knot east to northeasterly sustained winds with gusts over 40
knots along the Alaska Peninsula and Aleutian Islands through
tonight.

For Saturday, a blast of cold 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 tomorrow night.
Continuing through the weekend, expect wind chills to drop into
the 30s below zero as Arctic air continues to press southward.

&&

.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 and light winds will persist through the TAF
period.

&&