Heavy Freezing Spray Warning 213, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
453 PM AKST Mon Dec 6 2021

.ANALYSIS AND UPPER LEVELS...

The extremely active weather pattern across Southcentral
continues as a front pushes eastward across the state and the
Gulf. The front is enhanced by a strong southwesterly subtropical
jet located over the western Gulf, which aids in providing
moisture for the area and widespread precipitation for southern
Alaska. The precipitation has mainly been snow. Reports from Homer
indicate over a foot of snowfall accumulation since Sunday evening.
Low-level southerly flow has warmed temperatures enough to create
possible periods of rain or rain/snow mix for low elevation
coastal locations such as Whittier, Seward, and Homer. The
Anchorage Bowl continues to see only trace amounts of snow due to
persisting gusty southeasterly winds and downslope flow off the
Chugach Mountain range. Further inland and away from the
downsloping effects, areas across the Susitna Valley are
experiencing a steady snowfall, with reports of 19 inches of
accumulation in addition to reduced visibility as low as a 1/4
mile at times. A developing surface low is tracking along the
Alaska Peninsula and toward the Gulf. An upper-level shortwave
dropping in over the eastern Bering is currently trying to phase
with this surface low, likely creating more precipitation (mainly
snow) for the Southwest. Cold air advection over the Bering Sea
has produced snow showers and gales for areas out west.

&&

.MODEL DISCUSSION...

All models generally track the aforementioned surface low
northeastward along the Alaska Peninsula and over Shelikof Strait
through tonight, and then into Prince William Sound for Tuesday.
However, the GFS still wants to keep the low out of the Sound and
over the northern Gulf. The GFS has been a persistent outlier and
is once again keeping the low further south. Since all models
illustrate this as a relatively progressive weather system, the
surface low most likely will not stall out in the Sound and should
continue tracking toward the western Gulf into Wednesday.

Models show good agreement with a front pushing eastward across
the Bering Tuesday into Wednesday, dragging fast westerly flow
behind it. There is also increasing forecast confidence that a
strong low will track northeastward over the western Aleutians and
into the Bering starting Wednesday morning. This storm has the
potential to create high wind concerns along its track, so it will
be important to fine tune the low's path during the subsequent
forecast packages.

&&

.AVIATION...

PANC...A front has moved east ahead of the airport, so mostly VFR
conditions are expected through tonight with possible intermittent
rain/snow showers. Gusty southeasterly winds will diminish
throughout today and shift northwesterly sometime later this
evening which will create another round of wind shear conditions.
There is low confidence with the exact timing of this wind shift.
Tonight and during the early morning hours on Tuesday, snow sets
up again and will reduce cig/vsby to IFR conditions with
intermittent LIFR conditions possible.

&&.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

A strong surface low west of Kodiak Island moves into the northern
Gulf late tonight. Active weather will continue through tomorrow
night before briefly calming down. A warmer airmass follows the
front. Whittier and Middleton Island have already transitioned to
rain, with Cordova expected to follow by early tomorrow morning.
Homer is reporting a wintery mix this afternoon but will quickly
transition back to snow this evening. Regardless of above freezing
temperatures in both Homer and Cordova, the precipitation
intensity was able to overrun the warming and keep conditions all
snow for a longer duration of time today. Southern Kenai
Peninsula, primarily south of Clam Gulch, will see a transition
back to all snow tonight, and will see additional snow
accumulations of 6 to 10 inches, with highest amounts across Homer
Bluffs. Further north, snow makes its way to the Anchorage and
Mat-Valley areas. Steady snowfall begins tonight and will persist
through tomorrow, with highest accumulations along the higher
elevations, including the Upper Hillside. Snow will taper off to
snow showers later tomorrow afternoon with little to no additional
accumulations. A Winter Weather Advisory is out for the Anchorage
area, mainly for the Hillside, and an Special Weather Statement
is out for the Mat-Valley.

Once the low reaches the North Gulf Coast, it begins a
southeasterly trajectory shortly after, and winds across
Southcentral transition to northerly. The main concern following
the wind shift will be the onset of blizzard conditions along the
Richardson Highway from Paxson north. Light, fluffy snow has
fallen and will continue to fall through tonight and into
tomorrow, and will be easily transportable, even in lighter winds.
A Blizzard Warning has been issued for the area beginning Tuesday
morning and persisting through early Wednesday morning.
Additionally, the shift to northerly winds will also inevitably
allow for a gradual decrease in temperatures Tuesday night and
Wednesday.

&&

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

A fairly active pattern is expected across Southwest Alaska over
the next couple of days. Snow will gradually taper off across the
lower Kuskokwim Valley and Bristol Bay tonight. A front will move
across the Kuskokwim Delta and Bristol Bay from Tuesday evening
through mid-day Wednesday. This front will bring a round of light
to moderate snow with windy conditions. Visibility may be reduced
to one half mile or less across the Kuskokwim Valley in areas of
blowing snow. A Winter Weather Advisory has been issued for the
Kuskokwim Delta from 5pm AKST Tuesday through 12pm AKST Wednesday.
Strong southwesterly on-shore flow will continue through
Wednesday afternoon before easing. The break in the action will be
short- lived as a strong low pressure system will move over
Southwest Alaska on Thursday. This low will bring snow and strong
winds to the Kuskokwim Delta and Bristol Bay on Thursday and
Thursday night.

&&

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

A very active weather pattern is expected across the
Bering/Aleutians over the next few days as a strong low pressure
system moves across the area. This low is expected to track from
the North Pacific across the central Aleutians into the Bering Sea
and then move eastward into Bristol Bay. This low will produce a
widespread area of gale and storm force winds with hurricane force
gusts. A High Wind Watch has been issued for the Central Aleutians
for Wednesday afternoon and evening due to gusts expected to reach
80 mph at times. Winter Storm Watches were issued for the Eastern
Aleutians and Alaska Peninsula from Wednesday afternoon through
Thursday morning and Wednesday afternoon through Thursday evening
respectively. Due to the warm sector occluding as the system moves
eastward, temperatures will be colder across the eastern
Aleutians and Alaska Peninsula compared to points west. These
colder temperatures will allow for a greater chance of snow in the
Eastern Aleutians and Alaska Peninsula. Snowfall amounts will
generally range from 1-2" in these areas with higher amounts in
the mountains. However, the strong winds will allow for this snow
to blow around and significantly reduce visibility at times. With
respect to guidance, a GFS/NAM blend was the favored solution as
these models showed the most run to run consistency and similarity
in solutions when compared to the rest of guidance. Forecast
confidence remains above average with the track and intensity of
this strong low pressure system.

&&

.MARINE (Days 3 through 5: Thursday thru Saturday)...

A well-developed Central Bering low moves across the Alaska
Peninsula and Gulf of Alaska through Saturday. Confidence is good
for widespread storm force winds with local areas of hurricane
force winds with the low and front through Thursday, mostly over
the Bering. Widespread storm force outflow winds persist along the
Pacific side of the Alaska Peninsula, and over Shelikof Strait
and the Barren Islands through Saturday as the low and front moves
across the Gulf. A new North Pacific low and front approaches the
Western Aleutians with widespread gales for Saturday.

&&

.LONG TERM FORECAST (Days 4 through 7...Thu through Mon)...

Two separate steepening storms from the North Pacific are
strongly focused on making their way across the eastern Bering
into the Gulf of Alaska starting Thu through Mon. The first storm
is tracked to move through the Aleutians and Bristol Bay Thu
and Thu evening before crossing over the western Gulf Thu night.
The potential for rain/snow mix is feasible as warm temperatures
combined with tropical moisture feeds into the system along the
west to south flank of the low, causing steady rain to reach parts
of the south Alaska Peninsula and Kodiak Island. Much higher
gusts from the first low could occur mainly along the gaps and
passes of the eastern Aleutians through the south of Alaska
Peninsula into Kamishak Bay and Barren Islands through at least
Sun afternoon. Meanwhile, a second low barrels through the western
Bering while its associated front builds across the eastern
Bering/Aleutian Chain and Alaska Peninsula through Mon.
Essentially, the latter system could either stay over the Bering
through Mon or leap right into the western Gulf by Mon night as
the front turned into an open trough Mon evening extends over the
western Gulf. Clearly, these expected storms will continue to
bring wintery conditions, strong gales and storm-force winds
especially over the Bering, and increased snow accumulations for
the region the next several days. Also, the onset of these systems
could easily favor heavy freezing spray for the Bering, and the
potential for heavy snow and blowing snow for the Aleutians and
Southwest.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 141.
		 Winter Storm Warning 121 125 131 135 145.
		 Winter Weather Advisory 101 152 155 161.
		 Winter Storm Watch 181 185.
MARINE...Storm Warning 120 130 131 351.
		 Gale Warning 119 125 129 136-139 141 150 155 160 165
					  170-181 185 352 411-414.
		 Heavy Freezing Spray Warning 129 130 139 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AF
SOUTHCENTRAL ALASKA...KM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ED
MARINE/LONG TERM...CB/BL