Gale Warning 774, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
534 AM AKST Sat Dec 10 2022

.ANALYSIS AND UPPER LEVELS...

A ridge of high pressure continues to build in from the north and
west across interior Alaska, while a low weakens in the eastern
Gulf. Cold air advection along with tightening pressure gradients
between the Gulf low and high pressure is maintaining windy
conditions across much of the Gulf, and through bays and passes.
Skies are mostly clear across Southcentral under a dry, northerly
flow with overnight temperatures in the teens to single digits.
Out west, a frontal system associated with an occluded low near
Saint Matthew Island is moving east across the Bering Sea. A
wintry mix of precipitation along with gusty southerly winds are
occurring over the Alaska Peninsula, while snow and gusty
southerly winds are occurring over coastal Southwest Alaska.

&&

.MODEL DISCUSSION...

The latest operational model runs are in decent agreement with
the placement and intensity of synoptic scale features at both the
surface and in the upper levels. Overall, confidence is
increasing for an impactful winter storm event to occur this
weekend and early next week over Southcentral. An initial upper
level wave will arrive from the west, bringing snow across western
Kenai Peninsula, Anchorage Bowl, and Mat-Su Valleys tonight into
Sunday morning. A second and potent upper level wave then arrives
Sunday into Monday. Widespread, significant snow accumulations are
possible from the Kenai Peninsula northward to the Mat-Su
Valleys. The main challenge is the exact timing and where the
heaviest snowfall or precipitation will fall associated with the
secondary wave. Additionally, precipitation type for locations
along the northern Gulf coast remains a challenge.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist. Snow returns
across Southcentral beginning late tonight or early Sunday
morning.

&&

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

The clear skies over Southcentral are already beginning to give
way to increasing clouds from the southwest which herald the next
storm system. This will be a major storm for most of Southcentral
Alaska Sunday into Monday, with widespread heavy snow and areas of
gusty winds producing blowing snow.

The first round of precipitation will move to Kodiak late this
afternoon and then to the Kenai Peninsula and farther north
overnight. There is a question as to whether Anchorage and the
Matanuska Valley will see any snow Saturday night as this first
wave of the system will move through quickly and then produce
fairly strong easterly cross-barrier flow over the Chugach
Mountains and Kenai Mountains. This set-up should actually put
Kenai and Soldotna in the area of greater snowfall Saturday night.
The bigger issue will be the low on Sunday. This surface low will
track just to the east of the Kenai Peninsula Gulf coast as a
strong 500 mb trough approaches the area from the west. This will
combine to cause ample moist air from the Pacific over a thermal
gradient over the land which is a good combination for
precipitation. In addition., the warm air will remain over the
Gulf of ALaska keeping precipitation snow for all areas except for
Kodiak Island which will turn to rain overnight Saturday night,
and the immediate Gulf coast which may mix with rain before
turning back to snow. All Inland areas are under a Winter Storm
Watch due to snowfall amounts and intensities generally from
Sunday afternoon through Monday afternoon. There is also the
chance for blowing snow in the Kenai Peninsula along Cook Inlet,
as well as higher elevations including Turnagain Pass and Thompson
Pass. This storm has the potential to cause widespread travel and
transportation disruptions across Southcentral Alaska.

&&

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

A strong but weakening frontal boundary is arriving ever so
slightly ahead of schedule, with snow and gusty south to southeast
winds now extending along the coast from western portions of
Bristol Bay and up across the Kuskokwim Delta. Winter Weather
Advisories remain in effect for both regions due to mainly the
restricted visibilities from blowing snow with gusty winds
continuing along mainly coastal areas. As the front weakens,
conditions will improve as winds begin to relax and as snowfall
becomes more intermittent and showery. Additional snow
accumulations with this first round will be anywhere from 2 to 5
inches across western Bristol Bay, with perhaps up to 2 more
inches across the Y-K Delta.

The attention by this afternoon and evening shifts quickly to the
next impactful storm system expected to approach from the
southwest. A deepening low is expected to approach the southern
Alaska Peninsula (AKPen) later today as it moves generally towards
Kodiak Island and into the western Gulf. North of the center, a
new band of moderate snow will develop first over Bristol Bay,
then spread northeast into the Lower Kuskokwim Valley tonight.
This is anticipated to be a long duration event, with steady
snowfall not expected to end until the low pushes into the
northern Gulf Coast and as colder, drier air filters back into
place from the northwest late Sunday night into early Monday.
Storm total snowfall across Bristol Bay and Bristol Bay is
expected to range from 7 to 12 inches, with the heaviest amounts
focused across the eastern half of of the region closer to the
Alaska Range. Additional weather headlines may be necessary for
this next round of snowfall, so check back soon for further
updates.

Looking towards Monday, the return to more clear and cold
conditions will likely be cut short, with another low and
attendant front expected to reach the coast with another round of
precipitation by Monday evening and overnight. This will likely be
a more quick hit of snow, with mixing with rain possible along
the coast as the low approaches the Y-K Delta early Tuesday
morning.

&&

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

A front associated with an occluded low now moving past St Matthew
Island will move into Southwest and diminish by this afternoon.
Gusty westerly winds up to gale force will continue south of the
low center as it lifts north through tonight, namely across the
central and northern Bering near the Pribilofs and St Matthew. A
push of cold air moving southwest around the low will help kick
off snow showers across the eastern Aleutians and Pribilofs on
Sunday, while also aiding in the development of northwest gap
winds increasing to gale force out of bays and passes along the
southern Alaska Peninsula and eastern Aleutians through Monday
morning. Meanwhile, another low will move into the southwestern
Bering between Sunday and Monday, ushering gale force winds and
rain across the western Aleutians. The low and its attendant front
will arc east on Monday into Monday night, pushing gusty winds and
mainly rain across the rest of the Aleutian Chain and Pribilofs as
it advances towards the Southwest coast.

&&

.LONG TERM FORECAST (Days 4 through 7: Tuesday through Friday)...

Latest model solutions for Tuesday continue to depict a weakening
area of low pressure along the northern Gulf of Alaska coast,
weak ridging skirting the Eastern Aleutians, and a second area of
low pressure lifting northward into the western Bering. Across
Southcentral this will help to see snow decrease across the region
and winds to also diminish. However, a quick moving air mass of
colder 850 mb temperatures moving through the Copper River Basin
may see outflow winds temporarily linger along the Gulf coast over
the first half of Tuesday. High pressure then builds over the
region with warmer temperatures through Thursday.

Out west, ensemble guidance and operational models want to bring
a strong Kamchatka upper low into the western Bering by the middle
of next week. While there are differences in the overall
intensity of the low, placement of the low between ensembles and
even operational models is in relatively good agreement. The
placement of the low will result in strong southerly warm air
advection ahead of the low, including the Eastern Aleutians and
Alaska Peninsula. So much so that Southwest Alaska could see
anomalous warm temperatures and the predominant precipitation
type as rain. Over the Bering, models signal the likelihood of
gale to storm force winds, both ahead and behind the low. The
direction of winds would remain out of the south ahead of the low,
while out of the north behind the low. Furthermore, significant
cold air advection on the backside of the low and across the
western Bering would favor an even higher wind threat.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Watch: 101 111 121 125 131 141 145.
         Winter Weather Advisory 155 161.
MARINE...Gale Warning: 119 120 130 131 139 150 155 160 165
					   178 180 181 185 351 411-414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MF
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
LONG TERM...BL