Heavy Freezing Spray Warning 207, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
720 PM AKST Thu Dec 2 2021

.ANALYSIS AND UPPER LEVELS...

An upper level trough extends over the Alaska-Yukon border while
an upper level ridge axis is oriented north to south over the
central Bering. A surface low continues to spin over the northern
Gulf and is gradually drifting to the south. This has allowed any
remaining snow showers to diminish across Southcentral. A front
over the Western Aleutians continues to move eastward. Gusty
southerly winds across the western Bering and Western Aleutians
have been observed this afternoon with peak gusts near 60 knots.
Meanwhile over Southwest Alaska, conditions are clear and cold
though a stubborn stratus layer has remained in place over the
Kuskokwim Delta Coast today. Cloud cover in Southcentral continues
to dissipate as northerly flow returns.

&&

.MODEL DISCUSSION...

Model solutions are in good agreement with the synoptic pattern
through the short term and there is good agreement with the timing
of the front arriving over Southwest Alaska Friday. By Saturday,
a couple of differences arise in the upper level features, though
there has been consistent agreement on the development of a low in
the Gulf south of Kodiak Island. At this time, that low looks to
remain over the Gulf waters and shift east with no impact to the
mainland. By Sunday, the biggest challenge will be a large Bering
low and its associated front moving across the southern half of
the state. While models have been in generally good agreement with
this next system and consistent in advertising its track across
the mainland, there are many details to iron out, including the
timing of occlusion and how much warm air is able to work inland.
There is potential for this low to produce widespread snow across
Southwest and Southcentral Alaska, however many details still need
to be ironed out, which keeps confidence low at this time.

&&

.AVIATION...

PANC...VFR conditions and northerly flow will persist.

&&

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

An area of low pressure currently situated south of Middleton
Island is moving south and east, leaving mostly clear to party
cloudy skies across Southcentral. Meanwhile, upper level support
coupled with cold air advection will help maintain northwesterly
gale force winds funneling through the bays and passes near
Kamishak Bay to the Barren Islands. These winds will continue
across the western and southern Gulf through tonight before
subsiding to small crafts by Friday morning as low exits out of
the area and the pressure gradient relaxes. A surge of Arctic air
spilling across the Alaska mainland will allow temperatures to
drop down in the single digits to below zero across the coastal
areas and interior valleys over the next couple of nights.

Cold, dry conditions will prevail as a ridge of high pressure
dominates at least through Saturday. As we head late into the
weekend, a surface low will develop somewhere near Seward,
bringing a chance of snow along Prince William Sound late Saturday
night into Sunday morning. As the ridge axis moves east, a broad
longwave trough over the Bering Sea will shift over the eastern
half of the interior state and bring unsettled weather into early
next week. Moist, southwesterly flow aloft will develop along a
frontal boundary, with increasing chances of light to moderate snow
for all areas. This could be an active weather pattern so stay
tune for updates.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight
through Sunday)...

A much more active weather pattern is set to begin by the late
overnight hours tonight for parts of the area, namely over the Y-K
Delta area initially. A weakening but still powerful front will
rapidly move across the Bering tonight, arriving near the
Kuskokwim Delta Coast with southeast winds topping out at or near
gale force Friday morning. Steady snowfall will move inland with
the front, combining with falling snow to result in significant
blowing snow along mainly the Kuskokwim Delta coast. Guidance has
continued to keep this front and its wind field slightly stronger
at its final approach than previous model runs, with sustained
winds now expected to peak in the 30 to 40 mph range along the
immediate coastline. There was enough confidence for stronger
winds coupled with falling/blowing snow to replace the Winter
Weather Advisory with a Blizzard Warning beginning late tonight
for portions of the Kuskokwim Delta Coast. See the Blizzard
Warning product now in effect for additional details.

On Saturday, the aforementioned front will quickly lose integrity
as it moves further inland. Light snow will move farther east with
it across Bristol Bay and the Middle Kuskokwim Valley, with snow
letting up entirely by the afternoon. Most areas will receive 1
to 2 inches of new snowfall or less through midday Saturday,
except across the Y-K Delta, where storm totals through Saturday
of 2 to 5 inches are expected.

The break in the weather late on Saturday will prove very
short-lived, with a potentially major winter storm system looming
on the horizon by early next week. A large, deep low pressure
system will move across the northern Bering from Saturday night
into Sunday, with a very powerful front and a tropical moisture
tap surging out ahead right into Southwest AK. Very strong winds,
several inches of moderate to heavy snow, blowing snow, and
possibly even mixed precipitation may effect large portions of the
forecast area by Sunday, with multiple weather headlines
possible. Stay tuned to the forecast for updates as the details
for this significant storm system become better defined.

&&

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

A storm force front in the western Bering will weaken to gale
force as it moves towards the Southwest Coast early in the day on
Friday. A mix of rain and snow will follow the front as it moves
across, with mostly rain falling along lower elevations of the
Aleutians. A shortwave ridge will move in behind the front after
it moves inland tomorrow afternoon, with westerly gale force
winds spreading across the northern Bering and Pribilofs through
early Saturday morning. A much stronger system will enter the
picture on Saturday as a rapidly deepening low moving east of
Kamchatka sends another powerful front across the entire Bering
and Aleutians. Storm force winds and moderate to heavy snow
turning quickly over to rain will follow the front as it moves
across the Bering and Aleutians between Saturday and Sunday. A
second low center will drop southwest from Kamchatka into the
western Bering late on Sunday, bringing potential for more
westerly gale to possibly storm force winds.

&&

.MARINE (Days 3 through 5/Sunday through Tuesday)...

Bering/Aleutians...

Forecast confidence is low to moderate on Sunday and then becomes
low for Monday and Tuesday. A large low pressure system is
expected to move across the Bering/Aleutians at this time and
produce widespread gale force winds. However, there are
significant differences between guidance on the exact strength and
track of this low which is the reason confidence is low at this
time.

Gulf of Alaska...

Forecast confidence remains above average for Sunday and then
becomes moderate for Monday and Tuesday. Winds will remain below
gale force with no high seas expected on Sunday. Monday and
Tuesday there is a front moving through the Gulf and will produce
an area of gale force winds. Though there are differences between
guidance on the evolution of this front which makes for moderate
forecast confidence at best.

&&

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

Amplified troughing travels across the Bering/Aleutians Monday
and Tuesday, weakening as it moves across the Mainland towards the
Gulf. Areas of rain are likely along the Chain, as well as
increasingly gusty winds. Southwest may see periods of heavy
snowfall Monday, with some lingering light snow showers Tuesday
and early Wednesday. Models are hinting at cyclonic development in
the Gulf by Monday night, within the base of the trough. The low
development, in conjunction with the multiple shortwaves tracking
across the southern Mainland, will bring snow into Southcentral,
with the heaviest snowfall along the North Gulf Coast. A transient
ridge moves into Southwest Alaska overnight Tuesday through early
Wednesday afternoon before the next Russian front approaches the
Southwest Coast. The front reaches the Coast Wednesday, bringing
another round of show showers to Southwest. Simultaneously, a deep
low enters the Western Bering, quickly moving towards the Bering
Strait. The front pushes into Southern Alaska, looking to bring
another batch of widespread snow showers across the mainland.
Additionally, the GFS is currently indicating a warmer airmass
following the front, which may end up producing areas of rain
along the Southwest coast, specifically along the AKPen and
Bristol Bay, as well as across Kodiak Island (save the higher
elevations who will still likely see snow)

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm: 177 412 413.
Gale: 127 130 131 138 150 173-176 178-185 411 414.
Heavy Freezing Spray: 121 127-131 138 139 150 160 180-185 414.

&&

SYNOPSIS AND MODEL DISCUSSION...KO
SOUTHCENTRAL ALASKA...MF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
MARINE/LONG TERM...ED/KM