Small Craft Advisory 962, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
439 PM AKST Sat Dec 3 2022

.ANALYSIS AND UPPER LEVELS...

A broad upper level ridge stretches across the Alaska mainland
with a shortwave over the southern mainland moving over the top of
the ridge as it heads east. This shortwave is mainly producing
clouds with spotty showers across the Kuskokwim Delta. Farther
west a frontal boundary extends across the western Bering and
central Aleutians as it moves eastward. This front is producing
rain and gale force winds with 35 to 45 knots winds reported
across the Bering and Aleutians. A low pressure system south of
the eastern Aleutians continues to slowly move north. Temperatures
across the Aleutians range from the 30s at Shemya with 40s across
the rest of the chain and the AKPen. Southwest Alaska has warmed
up with temperatures in the mid to upper 30s. Across Bristol
Bay and the Kuskokwim River Valley it is a bit cooler with teens
at Sleetmute and 20s elsewhere. Across Southcentral temperatures
range from the 20s and 30s near the coast and higher elevations
above 1,000 feet with teens and single digits elsewhere.

&&

.MODEL DISCUSSION...

Models remain in good overall synoptic agreement through Monday.
However, there is disagreement with the progress of the front and
triple point low forming near the Kenai Peninsula Tuesday which
will affect the timing of the snow.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

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

The upper level ridge overhead will continue to slowly break down
and shift east as a series of shortwaves move into Southcentral
through Tuesday. Expect temperatures to slowly warm over the
coming days as cloud cover caps radiative cooling over most areas.
A fairly impressive inversion has set up as well with
temperatures warming to above freezing between 2700ft and 6700ft
on this afternoon's sounding in Anchorage.

A front and weak surface low will move into the region on Monday
bringing widespread light snowfall to the majority of Southcentral.
Upper level dynamics are fairly unimpressive, but the lack of
mid-level wind should also prevent any downsloping. There remains
some minor uncertainty on the start time of precipitation of a few
hours, but snowfall totals between 1 and 3 inches are expected
throughout the region on Monday. Southern coastal areas like Homer
and Cordova will likely see rain from this event, with Seward
expecting a mix of rain and snow.

A more robust system will move in on Tuesday, with good upper
level dynamics and jet support. Uncertainty in where this system
will set up as it crosses the Aleutian Range remains very high in
both surface low location and upper level vorticity fields.
Confidence is high that most of Southcentral will receive snow
through Wednesday, but timing and amounts are highly uncertain.

&&

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

A ridge of high pressure remains anchored over the mainland and
the global models are trending towards this ridge amplifying this
forecast period. On satellite imagery there is a mature low over
the Bering that is moving towards Southwest Alaska. Also on
satellite imagery (CIMSS mimic PW)there are two distinct modified
tropical fetches entrained into this low complex. Both of these
plumes literally extend back towards Hawaii. By Sunday the leading
edge of the precipitation shield will be at Nunivak and Bristol
Bay. The Alaska Peninsula will receive a hefty amount of
precipitation with this event. By Monday morning this front will
already be inland. Expect a short break. Then a second front will
come barreling across the Bering and is headed towards Western
Alaska...with the leading edge of the precipitation front at the
Nunivak and Y-K Delta Monday night. This too will be a fast moving
storm and the front will be inland by Tuesday morning. Expect
unsettled weather for the region.

&&

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

A progressive pattern is on tap. Back to back fronts will push
across the Bering this forecast period. Expect unsettled weather
complete with gusty winds, rough seas and . Expect gales out of
the bays and passes for the eastern Aleutians. In the wake of the
second frontal passage zonal flow will set up over the Bering late
Tuesday with isolated showers. The seas surface temperatures over
the Bering vary from 6 degrees Celsius near Attu to 0 degrees
Celsius near Nunivak. In satellite imagery, ice is beginning to
form around St Lawrence Island and along portions of Southwest
Alaska.

&&

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

An active pattern continues into next weekend as a parade of
storms transit the Bering/Aleutians and Southern Alaska. The
long term forecast begins on Wednesday with an upper-level trough
and associated surface low over the northwestern Gulf of Alaska.
There is general consensus for the storm to track to the
Panhandle by Thursday morning and spread northwesterly gale-force
winds across the northern and western Gulf. There is also
increasing confidence that Southcentral can expect cooler
temperatures and precipitation (likely snow, given colder
temperatures aloft) on Wednesday. In the wake of the low, an
upper-level ridge is advertised to build east over the Mainland,
tapering off precipitation across Southern Alaska for Thursday.

Out west over the Bering and Aleutians, models still struggle with
the track of a large North Pacific low. The deterministic GFS and
Canadian models both support the low center tracking into the
central Bering by Thursday afternoon, after which time agreement
begins to diverge between these two models. The GFS proceeds to
take the low across the Alaska Peninsula Friday morning and then into
the central Gulf by Saturday morning. The Canadian solution
splits the main low into two separate centers by Friday morning,
with one center lingering over the eastern Bering and the other
tracking from the Gulf to the Panhandle by Saturday morning. The
deterministic ECMWF is the outlier solution in that it tracks the
North Pacific low along the Aleutians through Friday morning and
then develops a stronger low center near the southern Panhandle by
Saturday morning. The ECMWF is also the weakest solution in terms
of central pressure and wind strength. Despite the ongoing
forecast uncertainties with this North Pacific low, there is
general consensus at this time for winds to reach at least gale-
force and for central pressure to hover near 980 mb during the
low's strongest stage.

There is very weak agreement for another low to inhabit the Bering
on Saturday; however, there are currently considerable differences
in this feature's strength and track. Thus, forecast confidence
decreases significantly towards the end of the long term forecast.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 150-172 174 178-185.
		 Storm 173 175 176 177
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...CJ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
LONG TERM...AF