Small Craft Advisory 76, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
425 AM AKST Wed Jan 26 2022

.ANALYSIS AND UPPER LEVELS...

An upper level trough is moving over southwest Alaska as a
secondary trough moves over the Bering Sea. The sencondary trough
is being forced into the first as a ridge builds behind it over
the western Bering. Farther west, a Storm Force low is moving over
the western Aleutians. Light snow is occurring beneath the
trough.

Meanwhile, a large low pressure system is moving north toward the
Gulf of Alaska. Abundant cloudiness associated with this low
continues to flow into the region, helping keep temperatures
across the Gulf Coast on the mild side in the 20s and 30s.

&&

.MODEL DISCUSSION...

Little has change with the overall pattern. Models continue to show
the development of a highly amplified blocking pattern. Although
guidance continues to show an omega block setting up from eastern
Russia to the Gulf of Alaska, there is still some uncertainty as
to how the various upper-level waves on the downstream side of the
block interact. The biggest challenge remains with how a
developing upper-level polar low over interior Southwest Alaska
interacts with the low lifting north into the Gulf, as the former
drops south over the AKPen.

Guidance also continues to show an inverted surface trough
developing over the northern Gulf with abundant mid-level moisture
streaming into the Southcentral coast as colder air advects over
the region from interior Alaska. Guidance is in good agreement
that there will be widespread precipitation, mainly in the form of
snow, across coastal Southcentral and Cook Inlet. The placement
and track of these features, however, will impact where the bands
of heaviest precipitation set up. While precipitation looks likely
along the coast, any shift in the placement of the upper-level
feature will have a significant impact as to if and how much snow
falls from Homer to Talkeetna Thursday into Friday.

&&

.AVIATION...
PANC...VFR conditions and light northerly winds will be the
predominant conditions for the Anchorage vicinity through most of
the TAF period, although cigs may briefly drop to IFR early this
morning. Introduced light snow beginning at around 10z tonight.
This may be adjusted forward or back a few hours.

&&

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

A North Pacific low that has been tracking towards the Gulf over
the past few days has gradually been trending further westward,
generating a rather good set up for significant amounts of snow
across Eastern Kenai and the Prince William Sound areas. Light snow
will begin this afternoon and gradually intensify through the
overnight hours. As the inverted trough cycles around the low,
precipitation will spread north and west, beginning with the
Copper Basin and then into Anchorage and Western Kenai tonight and
tomorrow. Additionally, the southern Susitna Valley may see
periods of snowfall overnight tomorrow. The inverted trough will
also end up tightening both the thermal and pressure gradients
near the Valdez/Thompson Pass areas. This is a good set up for
blowing snow to occur through Thompson pass. Winds will be
gradually increasing through today and tonight, with light snow
through the afternoon and evening picking up by tonight. Highest
impacts are likely during the early morning hours and will persist
through the early afternoon. As with all blowing snow events,
visibility reductions are to be expected, as well as periods of
heavy snow and gusty winds.

Northerly winds roll into Kodiak Island this morning, which may
bring a quick shot of snow before winds become northeasterly.
Advection of warmer air from the Gulf will transition snow to rain
later in the afternoon. This pattern may persist with a back and
forth between rain and snow through the end of the week.

In the upper levels, a trough squished between two ridges
amplifies and dives southwards towards the Gulf, absorbing remnant
energy from the weakening Gulf low, and develops a new system. The
new system meanders across the Kuskokwim Valley and Bristol Bay
Thursday night, ending up south of the AKPen by Friday. A majority
of forcing will be lost once the low moves south, which will
end the snow over western Southcentral by Friday.

&&

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

High pressure has moved into the region. Dry and bitterly cold
temperatures are expected this forecast period. Early this morning
areas of freezing fog have been detected over portions of
Southwest Alaska. Offshore winds will increase on Thursday
resulting in wind chills in the -30F to -35F range across the
Kuskokwim Delta. By Thursday morning, Bethel will have an actual
low temperature of -10F and King Salmon will plummet to -2F. The
thermal gradient will result in pronounced gap winds near the
Alaska Peninsula.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

The longwave pattern features a broad trough over the western
Bering. The models continue to track a 955 mb North Pacific low
across the western Aleutians and into Kamchatka. This morning,
surface low is approximately 350 NM south of Attu Island with a
broad tight pressure gradient. Already gusty winds have been
detected on ASCAT (Advanced Scatterometer) data near the western
Aleutians. As time elapses, the stronger winds will advance
northward. Expect storm force to gale force winds and rough seas
(+30 ft) along with a wide precipitation shield. There is a 1034
mb Arctic high over the Bering Strait which influences the
northern and eastern Bering. The leading edge of the ice shield is
approximately 50 nm northeast of St. Paul Island and it extends
well into Bristol Bay. Heavy freezing spray is expected south of
the ice edge.

&&

.MARINE (Days 3 through 5 - Friday through Sunday)...

Gulf of Alaska:

A North Pacific low lifting northward in the Gulf will bring
northwesterly gale force winds from Cook Inlet through Shelikof
Strait from Friday to Saturday afternoon. As the low weakens and
exits out of the Gulf Saturday evening, expect winds less than
35 kts and seas less than 20 ft. Forecast confidence is moderate
to high.

Bering Sea/Aleutians:

A low near the Kamchatka Peninsula will bring localized gale
force winds and elevated seas above 20 ft in the northwestern
Bering Sea on Friday morning.

A strong North Pacific low with an associated front will approach
the southern Bering Sea early Friday afternoon. Widespread gales
with a potential of storm force gusts and elevated seas above 20
ft will extend from the Western Aleutians to the northern Bering
Sea through Saturday. Forecast confidence is moderate to high with
most of the active weather staying west of the Pribilof Islands
and Central Aleutians.

Late Saturday night into Sunday, another North Pacific low will
approach the southern Bering Sea. There is a potential for
another round of gales and elevated seas extending across the same
regions and possibly in the Central Aleutians for the rest of day
Sunday. However, there is model uncertainty with the overall track,
position, and strength associated with this system. Therefore,
forecast confidence is low.

&&

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

Looking ahead in the extended forecast, the latest operational
model solutions seem decently clustered with the synoptic scale
features in the short term, but begin to diverge toward the end of
the period. Synoptically, an omega blocking pattern on Saturday
will be positioned over the western Alaska region with the
amplified ridge axis over the eastern Bering Sea. Downstream of
the ridge, a surface low interacting with a cold polar trough in
the Gulf will keep unsettled conditions for Southcentral with
moderate to heavy precipitation.

As the low exits out of the area, precipitation will taper off
from north to south by late Saturday. Benign conditions with
temperatures near to or below normal will prevail for the southern
mainland as the aforementioned ridge shifts over the state. From
Sunday onward, model spread has increased significantly with the
breakdown of the omega ridge as well as struggling with small to
mid scale embedded systems and interactions. Depending on
consistency of future models runs, unsettled weather may return
for the entire southern state as early as Monday as a storm
system with a good moisture fetch lifts northward into the Gulf.

Out west, a series of deep Pacific lows will move north across
the Western Aleutians, bringing periods of gusty winds, rain/snow
mix, and elevated seas at times into the northern Bering Sea.
Although there is uncertainty in placement, strength, and timing
with these systems, a wet pattern will be the main theme as we
head into the weekend. Some of the precipitation and wind may
extend across the Pribilof Islands, the Central/Eastern Aleutians,
and AKPEN for early next week.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 177-178 411.
         Gale Warning  119-120, 130-132, 138-139, 150, 155,
                       175-176, 185, 412-413.
         Heavy Freezing Spray Warning 139, 160, 165, 179,
                       185, 412, 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...NR
SOUTHCENTRAL ALASKA...KM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
MARINE/LONG TERM...MF