Gale Warning 847, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 PM AKST Sat Dec 24 2022

.ANALYSIS AND UPPER LEVELS...

At the upper levels, a large blocking high centered near the
Chukchi Sea extends south over the western Bering Sea and Aleutian
Islands. An Arctic trough is elongated across the southern Alaska
mainland and continues to spread a very cold airmass across the
Mainland, eastern Bering, and AKPen.

At the surface, a surface low and occluded front sits across the
northern AKPen into Bristol Bay while a cold front is south of the
AKPen. This frontal system is producing light snow across Kodiak
Island, the northern AKPen, and Bristol Bay.

Cold temperatures are evident across Southwest Alaska with single
digits to below zero temperatures with wind chills ranging from
-20 to -35 across the area with the coldest across the Kuskokwim
 Delta. Gusty winds are also occurring across the southwest with
 30 to 40 mph sustained winds and gusts up to 50 mph. Across the
 Pribilofs and Aleutians temperatures are in the 20s along the
 Pribilofs and 30s across the Aleutian chain. Temperatures along
 the AKPen are in the 20s across southern areas with single digits
 to teens across the northern AKPen. Gusty winds are also seen
 across the Pribilofs, Bering Sea, and eastern Aleutians with 30
 to 40 knot winds with lighter winds across the central and
 western Aleutians.

Over the gulf a compact surface low continues to spin across the
northeastern Gulf bringing light snow near eastern Prince William
Sound. Cold temperatures continued to be observed across
Southcentral with negative teens to single digits inland and teens
to 20s near the coast.

&&

.MODEL DISCUSSION...

Models are in good agreement through Monday with only minor
differences. The low bringing cold air into the Southwest and
Bering Sea is handled fairly well as it tracks west across the
Bering through Monday with only minor differences in the track
and position of the low. A frontal system with strong winds will
track into the Gulf Sunday and Monday with good model agreement.
Additionally, the parent low to this front will track towards
Kodiak Island with only minor differences in track and strength,
but overall it is handled well by all the models. The main
forecast challenges will be the possibility of blowing snow across
the Pribilofs through tonight and Sunday and the strength of the
Mat valley winds Sunday afternoon through Monday morning.

&&

.AVIATION...
PANC...VFR conditions will persist through this TAF period. Gusty
northerly winds are expected to gradually ease through this
afternoon and then increase tomorrow morning with gusts of 25 to
30 knots possible.

&&

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

A fairly active pattern will continue over the next few days
across Southcentral Alaska. Low pressure will move into the Gulf
on Sunday and will result in widespread gale force winds with
areas of storm force winds in the northern Gulf. These winds will
gradually ease as the low lifts northward through Monday night.
The biggest forecast challenge is snowfall amounts and
precipitation type across Kodiak Island and along the southern
coast of the Kenai Peninsula. The precipitation is likely to be
confined to the windward side of the mountains due to strong
downsloping on the leeward side as a result of strong cross
barrier flow.

There will be a persistent Matanuska Valley wind during the
period. However, this wind will remain in the 12-20 kt range and
gusts in the 20-25 kt range. A Wind Chill Advisory remains in
effect for Thompson Pass due to wind chill values reaching -40F at
times.

Temperatures will become warmer over the next few days across
Southcentral as the aforementioned low brings warm air advection
across the region.

&&
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Tuesday)...

A developing low pressure system in Bristol Bay will bring
significant snowfall accumulations and blowing snow to parts of
Bristol Bay tonight into Sunday morning. Some adjustments have
been made to the Winter Weather Advisory with the location of
heaviest snow accumulations and lowest visibilities from blowing
snow. Snow accumulations up to 10 inches can be expected through
the morning hours along a line from north and west of Dillingham
to the Alaska Peninsula between King Salmon and Pilot Point.
Snowfall accumulations approach zero rather abruptly east of
Koliganek and King Salmon. Areas that see snow will be at risk for
half mile visibilities as strong northerly winds continue to flow
offshore. Low visibilities will end with the snow from east to
west on Sunday morning as the low pressure system exits into the
Bering Sea.

Elsewhere, the strong northerly offshore winds will be the main
weather influence keeping Southwest Alaska cold through the short
term. Wind chills in the -30s continue this evening in parts of
the Kuskokwim Delta and Lower Kuskokwim Valley before temperatures
begin to warm Sunday morning. The warming will be most pronounced
in the lee of the Aleutian Range, as well as the Kilbuck and
Ahklun Mountains where easterly flow aloft is causing
downslope compressional warming. This will gradually lead to the
development of a very thin layer of warm air aloft across
Southwest Alaska as a low in the Gulf approaches on Sunday. Some
scattered, light precipitation will be possible over Bristol Bay
Sunday and Sunday night in the presence of this warm layer, which
may lead to some sleet mixing with snow at times. Then, colder air
works in on Monday as the low moves in over Southwest Alaska.
Light snow will be the result Monday and Monday night, primarily
over Bristol Bay, with accumulations of only a few inches
expected.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Today
through Tuesday)...

A surface low centered in Bristol Bay this evening will track
westward into the eastern Bering Sea tonight. Ahead of the low,
widespread light snow will develop and move across the Pribilof
Islands. This is now expected to occur while 40 mph northerly
winds are still streaming across the Bering. Blowing snow will
therefore be likely tonight for the Pribilofs and last through
Sunday morning, when the low center tracks near the islands and
winds begin to diminish. The system then continues westward
through the Bering on Sunday before dipping south toward the
Aleutian Islands by Monday. Snow amounts of two inches or less are
expected with this system for the central and western Aleutians.
Calmer weather returns for Tuesday as winds gradually diminish
across the Bering.

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

The overall pattern for the first half of the extended outlook is
likely to remain about the same, with a broad Aleutian low
drifting slowly along and south of the Aleutian Chain out west
through at least Friday. A loosely-defined longwave trough will
persist aloft across the Bering, resulting in an unsettled pattern
out west with gusty winds likely in gale force range wrapping
around the main low at the surface near the southern Bering on
Wednesday and Thursday. Light onshore flow over Southcentral
should keep any areas of snow and coastal rain confined near the
Prince William Sound, eastern Kenai Peninsula and across Kodiak
Island, with most inland areas remaining dry and seasonably mild.
Very weak steering flow again should result in very slow
progression of both the larger scale pattern and smaller waves
rotating around the Bering trough/low, with the vast majority of
the Pacific jet likely to remain well south of the outlook area
until the end of the week. This weak steering also causing models
to struggle with the handling of smaller scale features, with the
details for individual perturbations really falling apart by
Thursday and Friday.

There are some early indications for a shift in the pattern to
commence by Saturday, as the low meandering near the Aleutians
finally begins to shift into the western Gulf and amplifies the
upstream ridge over the Gulf and portions of Southcentral. This
could result in much heavier precipitation spreading along the
coast between Kodiak and the Prince William Sound by this weekend.
However, large model spread by this point in time still leaves
much of the remaining details left to be determined.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...
Winter Weather Advisory: 195, 161
Wind Chill Advisory: 131
MARINE...
Gale Warning: 127, 136, 137, 139, 150, 160, 179, 180, 181, 185,
			  411, 412, 414, 352
Storm Warning: 119, 120, 130, 131, 132, 138, 351
Heavy Freezing Spray: 139, 140, 160, 179, 180, 185, 412, 414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...ED
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
LONG TERM...AS