Small Craft Advisory 233, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
502 PM AKDT Wed Mar 16 2022

.ANALYSIS AND UPPER LEVELS...

A deep and cold upper level low which dug south across western
Alaska is now stalling along the Alaska Peninsula. Cold air
advection has largely ended across Southwest Alaska, the Bering
Sea, and Aleutians - as the cold air has already moved through all
the way down into the North Pacific. However, tight surface
pressure gradients, a strong jet aloft between the low and a
strong ridge over the western Bering, and steep low level lapse
rates (7 degrees Celsius or greater on the Cold Bay and Saint Paul
soundings this morning) continue to produce gusty northerly winds
across the eastern bering Sea, eastern Aleutians, and southern
Alaska Peninsula. In addition, a short-wave trough rotating
southward to the west of the low center is enhancing downward
motion in the atmosphere and contributing to strengthening low
level winds as it moves through.

To the east of the upper low center, a series of short-wave
troughs are tracking north across the Gulf of Alaska and toward
Southcentral. The western-most short-waves are beginning to be
pulled northwestward into the upper low circulation. These
short-waves are quite weak, so the resultant precipitation over
Southcentral is generally light in nature and mostly confined to
the coastal zone. Further west, an area of steady light snow has
formed over Bristol Bay, primarily from King Salmon northward.
At the surface, there is a weak low over the northwest Gulf with
a rapidly dissipating front along the north Gulf coast. As a
result, winds are diminishing across the region. A cold front
extending south from the low center has begun to track northward
across the western Gulf and Kodiak Island in response to the
steering flow aloft around the upper low center.

&&

.MODEL DISCUSSION...

Model guidance remains in pretty good agreement with the evolution
of large scale features over the next few days. There are some
differences in the depiction of upper level short-waves crossing
Southcentral Alaska tonight through Thursday which will affect
which inland areas see snowfall. There has also been a shift in
timing of interaction of trough rounding the upper low center with
a separate short-wave and developing surface low crossing the
North Pacific. The end result is similar, with a deep low moving
into the Gulf Thursday/Thursday night. However, the low and
associated frontal system initially settle farther south than in
prior model solutions. This means the bulk of impacts of strong
winds and heavy precipitation will remain over the Gulf. There are
some minor differences with the track of this low across the Gulf
Friday/Saturday along with track of short-waves moving overtop
of the low and toward Southcentral. This results in decreasing
confidence in the overall forecast as we head into the weekend.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist through tonight.
A weak short-wave trough will approach Anchorage Thursday morning,
likely leading to a period of light snow with MVFR conditions.
While there is uncertainty in exact timing of snow and lower
conditions, it will be brief (on the order of 3 hours or less).
Expect conditions to rapidly improve back to VFR as the short-wave
and associated snow lift northward midday Thursday. Coincident
with the snow, winds will shift from northerly to southerly, but
will remain below 10 kts.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Tonight through Saturday)...

A few areas of interior Southcentral will have a chance to see the
sun set this evening where breaks have developed in the multiple
cloud layers streaming north around an upper level low centered
over the Alaska Peninsula. Meanwhile, steady snowfall will
continue along the north Gulf Coast and Prince William Sound with
the moist onshore flow, with mixing with rain this evening likely
to continue with warmer temperatures near sea level (including
Seward, Portage and Whittier). Early Thursday, an easterly upper
level wave moving around the upper low to the west will move into
the Kenai Peninsula and up towards the Susitna Valley by midday
Thursday. As this wave progresses north and west, a surge of cold
air wrapping into the upper low out west will move out of the
western Gulf northeast into the Cook Inlet region. This push cold
air should provide enough lift to support a band of snow showers
progressing north along with this effective cold front, moving up
along the eastern Kenai Peninsula early tomorrow morning, then
into the Anchorage area closer to Noon. The frontal feature and
associated shove of cold air will stop short near the northern end
of the Cook Inlet as the upper level wave exits into the western
Alaska Range, so most areas across the Mat-Su Valleys to the north
to stay mostly dry tomorrow.

By Thursday evening, a North Pacific low will pivot north into the
southern Gulf, sending gale force winds back across most of the
open Gulf waters well into Friday. East to southeast winds will
once again increase along the coast as low's occluding front lifts
north, supporting increasing mountain snow and coastal rain-snow
mix across the eastern Kenai Peninsula and western Prince William
Sound on Friday, lingering into Saturday as the low and it's front
stall out over the Gulf. This same frontal axis will bend west
across Kodiak Island on Friday, with cold low level temperatures
and northerly flow likely supporting snow ahead of the frontal
passage on Friday morning. Around 3 to 5 inches of new snowfall is
possible in Kodiak City Friday morning before precipitation turns
over to rain as winds become easterly and temperatures warm by
Friday afternoon and evening. Meanwhile, most of interior
Southcentral will still see intermittent cloud cover, but should
stay mostly dry going into the weekend.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: This
afternoon through Saturday)...

A low pressure system moving very slowly over the northern AKPen
will bring light snow to the Bristol Bay area. Expect another 1
to 3 inches of snow through tonight before tapering off Thursday
morning. A shortwave will rotate around the low Thursday afternoon
through early Friday morning bringing light snow to the Kuskokwim
Delta with an inch or less of snowfall expected. As the low
slowly moves into the Gulf another shortwave will bring periods of
light snow from Friday afternoon into Saturday with light
accumulations expected. Otherwise winds will remain brisk across
the Kuskokwim Delta especially Thursday and Saturday with below
normal temperatures continuing into the weekend.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: This
afternoon through Saturday)...

Cold air from the Arctic will continue to move across the Bering
through Thursday with areas of Gales across the northern and
eastern Bering with the strongest winds south of the eastern
Aleutians and AKPen with storm force gusts out of bays and passes
through at least Friday and possibly into Saturday. Another
shortwave with cold air will move out of Siberia and push
southward across the Bering late Thursday through Friday producing
a wide swath of Gales across much of the Bering Thursday through
Saturday. Otherwise expect snow showers south of the ice edge
across the northern Bering and extending south to the Aleutians
and AKPen. Expect severals inches of snow across the eastern
Aleutians and AKPen over the next three days as cold air continues
to produce snow showers through at least Saturday.

&&

.Marine (Days 3 through 5: Saturday through Monday)...

Gulf of Alaska: A well developed low exits the Southwestern Gulf
as a second well developed low enters the Southcentral Gulf on
Sunday. The second low moves to the Southwestern Gulf for Monday.
Forecast guidance is good. The wind wrapped first low brings high
end gales across the Gulf and through Cook Inlet, Barren Islands
and Shelikof Strait, diminishing Sunday. Gale force gap winds
continue along the Alaska Peninsula through Monday. The wind
wrapped second low spreads high end gales over the Gulf with
possible storm force winds South of Kodiak Island through Monday.
Seas to 12 feet over the Northern Gulf and to 18 feet across the
Southern Gulf through Monday. Freezing spray possible South and
West of Kodiak Island Saturday.

Bering Sea: The Western Bering high pressure continues its
Southward track, with its North side ridge moving across the
Bering through Monday. Several troughs move over the Eastern
Bering through Monday. Widespread high end gales move over the
Eastern Bering, Aleutians and Alaska Peninsula, diminishing over
the Bering Monday. Gap winds persist along the Pacific side of the
Aleutians and Alaska Peninsula through Monday. Seas to 20 feet
over the Bering side of the Central and Eastern Aleutians and
Alaska Peninsula through Sunday, subsiding. A front approaches the
Western Aleutians and Bering for Monday. Gusty winds increase to
widespread high end gales across the Western Aleutians and Bering.
Seas building to 20 feet for Monday. Freezing spray expected in
open waters over the Western and Central Bering through Saturday.

&&

.Long Term Discussion (Days 4 through 7: Sunday through Wednesday)...

The latest operational model runs and ensemble means are decently
clustered with the evolution and progression of the synoptic
scale features, but diverge in the specific details towards the
end of the period. Models seem to have a general consensus will be
a long wave pattern through early next week, with a broad trough
persisting over Mainland Alaska through Monday.

Meanwhile, an upper level low will be positioned somewhere in the
central Gulf that will pinwheel a series of shortwaves and
associated surface lows northward. Even though there is a good
amount of discrepancy and variability with these shortwaves, most
of the precipitation will be concentrated through the Panhandle
and up into the southern coasts. Much of the mainland should be
relatively dry during the period, with the exception for potential
snow showers by late Sunday in the eastern interior. Otherwise,
temperatures are expected to be below normal across the coastal
areas and interior valleys, but trending toward normal next week.

Out west, a ridge of high pressure will build across the Bering
Sea. A reinforcement of cold air advection will help drive
northerly winds funneling through the gaps and passes of the
Alaska Peninsula and Eastern Aleutian Islands. Wrap around
moisture on the backside of the aforementioned upper low will
bring occasional snow showers into these regions later this week.
A drying trend commences on Monday as the ridge axis shifts over
the western mainland, while a gale force front extending from a
Kamchatka low moves slowly east across the Western/Central
Aleutians. From Tuesday beyond, there is considerable spread how
far the front progresses with a variety of solutions over the
Bering Sea and Gulf of Alaska.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 119 132 155 165 170-172 180 181.
		 Heavy Freezing Spray 165 179-185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...AS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RC
MARINE/LONG TERM...MK/MF