Heavy Freezing Spray Warning 16, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
458 PM AKST Fri Jan 8 2021

.ANALYSIS AND UPPER LEVELS...

A surface low centered over southern Cook Inlet, near the Barren
Islands, continues to be the primary weather-maker over Southern
Alaska this afternoon. To the east of the center, significant Gulf
moisture continues to move into the north Gulf Coast, keeping the
weather active especially through the Kenai Mountains. This is
also keeping temperatures well above seasonal averages, though
most areas away from any downslope wind influence remain below
freezing. The 12Z Anchorage sounding shows the usual nocturnal
inversion in the lowest layers, rising above freezing through
about 925 mb, then remaining very unstable above that all the way
up to the tropopause. The atmosphere is also a bit more saturated
as compared with yesterday throughout the entire profile, so any
moisture that can get over the mountains, has a better chance of
at least resulting in some flurry activity.

West of the low center, deformation banding persists over interior
Bristol Bay, with snow occasionally falling moderate at times in
Iliamna this morning. The activity persists to varying
intensities across much of Bristol Bay. Across the Bering, the
next sprawling low is moving across the western and central
Aleutians this afternoon. Temperatures are right near freezing, so
a mix of rain and snow is likely with the leading front. Snow
showers are prevalent across much of the eastern Bering ahead of
that low. A few lightning strikes have also been noted in the dry
slot convection southwest of Adak.

In the upper levels, a very wavy jet stream is prevalent across
Alaska, with the North American ridge over the Yukon, then a weak
west-east oriented jet streak across the Gulf, and a trough over
the Bering, with an embedded upper level low approaching the
western Aleutians, corresponding to the strong surface low. A very
impressive 210 kt zonal jet streak extends westward, feeding the
Aleutians low.

&&

.MODEL DISCUSSION...

In similar fashion to yesterday, the models remain in decent
agreement synoptically, tracking several large (and thus, easily
tractable) lows, but the finer details of any disturbances
rotating around the low center and are more likely to produce
impactful weather remain very low confidence this afternoon. Thus,
overall forecast confidence is high, especially across inland
areas where little in the way of precipitation is expected except
some upslope snow in the western Susitna Valley.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Some snow
shower activity is possible tonight with an approaching
disturbance, that may briefly drop conditions to MVFR, but is not
expected to be impactful at the airport. Behind the disturbance,
the Turnagain Arm winds will move across the airport, with gusty
southeasterly winds and warmer temperatures expected through the
morning, with the winds diminishing and returning to northerly by
midday Saturday.

&&

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

Multiple lows and upper level waves track across the Gulf and
Southcentral region over the next few days. Weak remnants of a
surface low linger just west of the Barren Islands throughout the
rest of this afternoon. The upper level reflection exists as a
open wave moving southeast to northwest across the Gulf and
Southcentral Alaska tonight. A band of precipitation ahead of the
wave impacts the Western Susitna Valley tonight into tomorrow.
Otherwise, Anchorage and areas north should remain relatively dry
seeing little to no precipitation through tomorrow night. Gusty
Turnagain Arm winds are expected to bend into Anchorage late
tonight into tomorrow morning, increasing temperatures in
Anchorage and along the Upper Hillside tomorrow. The majority of
the precipitation will continue to remain over the coastal areas,
with Western Prince William Sound/Eastern Kenai Peninsula seeing
the heaviest rain and snowfall through Monday. Persistent snow and
periods of rain is expected along eastern Turnagain Arm throughout
the next few days. There may be a brief lull in precipitation
tomorrow for the Cordova/Valdez areas as a second low to enter the
Gulf remains further south than the previous one.

The second North Pacific low approaches the Southern Gulf
tomorrow night and moves towards Kodiak Island, bringing rain
showers back to Kodiak tomorrow evening. This system then merges
with another one moving east across the Aleutian Chain tonight,
creating one large complex system. The associated front pushes the
North Gulf Coast late Saturday night, returning rain and
rain/snow mix to the Cordova/Valdez areas. Additionally, a barrier
jet sets up along the North Gulf Coast Saturday night into
Sunday, as well as strong winds and high seas down Cook Inlet and
west of the Barren Islands.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
A weakening shortwave trough moving over the Southwest Mainland
this evening will bring continued snow to interior Bristol Bay
and the Kuskokwim Valley. This wave should bring another 2-3
inches through Saturday morning, mainly to areas north and east of
Dillingham. Afterwards conditions should become dry, but cloudy
for most of the area as deep southerly flow aloft continues.

This cloudcover should also help to keep temperatures over the
next 2 nights warmer than initially expected, especially along the
Kuskokwim Delta. As a result wind chills in the Kuskokwim Delta
are now only expected to drop to near 20 below tonight, and not to
30 below or colder as was initially expected.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
A deep storm force low will continue tracking into the Central
Aleutians tonight. A large amount of cold air is also associated
with this front, which is allowing precipitation type to remain
as snow with temperatures hovering around freezing. When
accompanied with storm force winds, this has produced near
blizzard conditions in the Adak area today, but with warmer air
quickly moving in from the west this is not expected to last much
into the evening. This front will then track towards Dutch Harbor
for late Saturday were it will bring snow and blowing snow into
Sunday. By late Sunday low will move east of the AKpen, allowing
for broad northerly flow to setup throughout the Bering, that
should allow for the development of widespread snow showers.

&&

.MARINE (Days 3 through 5...Sun through Tue)...

Gulf of Alaska: The Gulf will continue to feature various areas of
low pressure moving quickly from south to north during the period.
Model agreement is very poor in this timeframe, so forecast
confidence is low. The best chance for gale-force winds will
remain close to the barrier jet region along the coast, primarily
late Sun into Mon. Winds and waves should start to come down a bit
on Tue with nothing more than small craft winds expected during a
short break between systems.

Bering Sea: Gale-force easterly winds early in the weekend will
give way to small-craft north to northwest winds on Sunday. These
winds will persist and continue to diminish Monday through
Tuesday. Seas will follow suit subsiding through the period.

&&

.LONG TERM FORECAST (Days 3 through 7)...There is a massive amount
of disagreement in the long term portion of the forecast. The
general idea will continue to feature cold air feeding down from
the Bering Strait through the Aleutians. This will continue to
produce some small scale polar low type features moving from north
to south, but it would be nearly impossible to nail down any
details with those at this time. Several more strong lows will
move into the Gulf of AK. This will keep warm air moving from
south to north and continually trying to intrude into
Southcentral. The warmest periods will coincide with the
strongest southeast winds across the mountains, especially if any
of these winds can mix down to the surface. On the western
periphery of the systems in the Gulf and the cold air over the
Bering, this location will provide the best chance for snow and
potential headlines. Right now this area lines up over Southwest
AK. But again, with high model uncertainty, all components of the
forecast will need further refinement.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...SPS zone 125.
MARINE...Storms 119 120 130 131 139 170-176 351 413 414.
 Gales 132 136-138 155 160 165 177 179 180 185 352 411 412.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JW
SOUTHCENTRAL ALASKA...KM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
MARINE/LONG TERM...AS