Heavy Freezing Spray Warning 54, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
351 PM AKST Wed Feb 3 2021

.ANALYSIS AND UPPER LEVELS...

Analysis shows strong high pressure over the eastern Pacific with
a ridge edging north into the Gulf of Alaska, and a strong low
pressure system rotating over Kamchatka with an attendant front
stretching southeast across the western Aleutians. Between the
two, a fast moving shortwave is moving east across southwest
Alaska.

At the surface, an area of weakening low pressure continues to
move east toward Southeast Alaska. Temperatures range from around
30 degrees in the Prince William Sound area and the 20s to around
30 degrees at other coastal areas, quickly dropping into the
single digits and teens at most other areas. The coldest readings
are in the teens below zero in the Copper River Basin area.

Gale force winds and waves can be seen along the western Bering
and Aleutians as the front continues across the area.

&&

.MODEL DISCUSSION...

Models remain in fairly good agreement on synoptic features
through the next several days. The weak shortwave approaching
Southwest Alaska will continue to weaken as it moves east across
the state overnight into Thursday, with little effect. The main
feature to watch is the approaching system forecast to move across
the Aleutians Thursday into Southcentral for Friday, bringing a
good chance for snow.

&&

.AVIATION...

PANC...Expect MVFR conditions to continue, as no good push to
scour it out. Any additional snow this afternoon will be very
light, little more than flurries. Fog may develop in the vicinity
overnight, but the environment favors a stratus deck over fog, so
if anything does form it should be isolated in nature and likely
won't move over the terminal.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Wednesday through Friday)...

The synoptic pattern features a low in the Gulf at the surface
and an upper level trough over the Yukon-Kuskokwim Delta, with an
arctic trough over the Brooks Range. There are numerous embedded
shortwaves from western Alaska to the Gulf of Alaska. The
disturbance that brought snow to most of Southcentral overnight
has moved through the Cook Inlet region as of early this morning
and is headed towards the Copper River Basin by late this
afternoon and evening. Stratus and patchy fog will persist in the
Cook Inlet and other portions of South Central.

An upper level ridge will move across western Alaska and into
Southcentral Alaska on Friday. This is a fast moving feature. In
its wake, the models bring a slug of upper level energy across
Kodiak and Cook Inlet late Friday and Saturday. This is our next
potential snow maker for portions of Southcentral, but again only
light accumulations are anticipated for the Anchorage Bowl. This
strong lobe of vorticity will move across the northern Gulf and
towards Cordova and Glacier Bay National Park. This pattern will
bring strong winds to the Barren Islands and Hitchinbrook
Entrance.

&&

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

Low stratus and fog has been the dominating weather across
Southwest Alaska earlier today, which will continue throughout
the evening for some areas. An upper level wave over the Kuskokwim
Delta and Valley will continue to produce snow showers before
tapering off for Thursday morning. A quieter weather pattern sets
up through late Thursday, with most of Southwest Alaska drying
out. The pattern shifts as a front moves over the coastal areas by
Thursday night, which will then spread farther inland throughout
the day on Friday. Blowing snow is possible for locations along
the Kuskokwim Delta Coast as the front brings stronger winds, but
there is still uncertainty in the timing of the front and
heaviest snowfall. Snow accumulations of a few inches are expected
as this system moves quickly across the region. Models have come
into better agreement today, allowing for forecast confidence
to increase. This system exits the region by Saturday morning,
with a few lingering showers, before the clear conditions set back
up across the Southwest mainland for the weekend.

&&

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

A gale force front over the central Bering this afternoon will
continue its eastward path, bringing widespread precipitation
from the Pribilofs to the central and eastern Aleutians through
the evening hours. Precipitation will stay mostly rain, or a mix
of rain and snow with this warmer system before the colder air
begins to move back into the region by Friday morning. The front
will reach the AKPEN Friday morning as it continues to weaken.

After this system diminishes, a much more uncertain pattern sets
up over the western Bering and Aleutians as the models are having
a difficult time with a compact low feature trying to develop on
Thursday into early Friday. However, models come back into good
agreement by Friday afternoon with a much larger frontal system
beginning to move over the western Aleutians and Bering. Storm
force winds will accompany this system over the western Bering
through Saturday afternoon.

&&

.MARINE (Days 3 through 5: Saturday through Monday)...

Gulf of Alaska: A low exits the Southeast Gulf Sun. Model tracks
differ slightly, but confidence is good through Mon. Widespread
westerly gale force winds and waves with high end gale force gusts
are expected over the Gulf Sat. These will diminish to small
craft winds Sun, and continue weakening for Mon. Wave heights to
21 feet Sat move across the Gulf, subsiding to 10 feet Sun. They
continue to subside as high pressure moves into the Gulf through
Mon.

Bering Sea: Eastern Bering high pressure yields as a front over
the central Bering swings into the northern Bering Mon. The low
with this front moves into the western Bering before retreating
near the Kamchatka Peninsula. Model development is mixed, but
confidence is improving through Mon. Widespread southeast gale
force winds and waves with high end gale force gusts diminish over
the central Bering Sun. Easterly small craft winds continue over
the Bering through Mon. Wave heights to 24 feet over the western
Bering and the Pacific side of the Aleutians through Sun will be
subsiding. Expect waves to 20 feet over the central and eastern
Bering through the forecast period.

&&

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

The long term pattern features an amplified upper level ridge
over the Gulf and southern mainland, while upstream, a deep upper
level low will drop southward from Siberia over the western
Bering. By Monday, the pattern shifts slightly as the ridge moves
eastward and becomes broadened across the Aleutian Chain. As
another low arrives over the western Bering, the ridge becomes
highly amplified once again by Tuesday. This will result in a
pattern change over the Bering with much more warm southerly flow
expected for Tuesday, while for the mainland, a much colder Arctic
airmass remains in place. By Wednesday, the strong ridge continues
to build within close proximity of a deepening upper level low
over the mainland. This, combined with a strong temperature
gradient will likely increase winds across the southwest coast of
Alaska. This setup also results in a somewhat regressive pattern,
as several upper level waves will steer systems from east to west
through the middle of next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale: 165 173 175 176 178 185 412 413.
Heavy Freezing Spray: 160 180 185.

&&

SYNOPSIS AND MODEL DISCUSSION...MIC
SOUTHCENTRAL ALASKA...PJS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...KZ/KO