Brisk Wind Advisory 36, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
517 AM AKST Sat Mar 2 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Monday night)...

A short-wave trough is tracking southeastward across eastern
Prince William Sound and the Copper River Basin early this
morning, along the east side of a low-wavelength high-amplitude
ridge shifting eastward from the Bering Sea to western Alaska.
Deep and strong northerly flow, low level Arctic air, and tight
surface pressure gradients continue to produce windy conditions
across much of Southcentral. Some of the strongest winds are
being observed in the Matanuska Valley and in Valdez, with gusts
to around 50 mph. Similar to yesterday morning, temperatures are
in the single digits to teens across much of Southcentral, with
sub-zero temperatures a little more widespread over the southern
Susitna Valley, east Anchorage and Eagle River, as well as the
Copper River Basin. The southward progression of the upper trough
has pushed all precipitation offshore into the northern Gulf, with
clear skies for Southcentral except the Cordova area and
southeastern Copper River Basin.

The upper level ridge will slowly move in from the west, moving
overhead of Southcentral and the Gulf on Sunday. This will finally
allow winds to diminish across the region, with calm to light
winds settling in for most of the region tonight. An extensive
cirrus shield is moving up and over the ridge now and will arrive
in Southcentral tonight. Despite the high clouds, the air mass in
place is quite cold and will support temperatures dropping below
zero for all except coastal locations tonight through Sunday
morning.

Upstream of the ridge, a rapidly weakening front looks like it
will dissipate before reaching the Gulf and Southcentral on
Sunday. Still, a weak upper level short-wave combined with
upslope flow and overrunning will be enough to produce areas of
light snow from Kodiak Island northward the western half of
Southcentral. The best chance of some very light accumulation
will be on Kodiak Island and the coast of the southern Kenai
Peninsula. A much stronger upper level short-wave and marginally
stronger surface front will move into the region Monday through
Monday night. All signs point toward development of a triple point
low in the northwest Gulf late Monday as the upper level short-
wave tracks eastward across the Gulf. Thus, expect the bulk of
precipitation and wind with this system to affect Kodiak Island
and the north Gulf coast/Prince William Sound. The front will
advect in enough warm air to cause a change-over to rain for
Kodiak, but the development of the triple point low should block
warm air advection into Southcentral and keep precipitation as
all snow.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Today through Monday)...

A decaying low over the Russian Far East extends an occluded front
across the Bering Sea, progressing slowly eastward through the
Pribilof Islands, eastern Aleutians, and Alaska Peninsula this
morning. A mix of precipitation types are associated with this
front, with a significant warm nose aloft leading to sleet and
freezing rain in places as the front moves through. These
precipitation types already ended in the Pribilof Islands earlier
this morning, with the back edge of the front producing only a
mix of rain and snow as surface temperatures warm and air aloft
cools with the passage of the occluded front. While sleet has
likely only just begun (in the past few hours or so) for Cold Bay
and King Cove, locations along the Alaska Peninsula can expect the
robust warm air aloft in the warm sector between a leading warm
front and trailing cold front to bring to some freezing rain this
morning, which could produce up to a tenth of an inch of ice
accumulation. However, the slow eastward progression of the front
will allow the warm air aloft to moderate and cool down through
the day. This means that further up the peninsula, Sand Point and
Nelson Lagoon will likely only see sleet mixing in with snow later
this morning, and a (low) chance of a trace of freezing rain. By
Saturday evening, the threat of freezing rain will come to an end
as surface temperatures warm and the occlusion reaches the Alaska
Peninsula. After that point, precipitation will likely fall as a
mix of rain and snow.

The slow moving front also reaches the Kuskokwim Delta coast and
the Western Capes of Bristol Bay today. Out ahead of the front,
blowing snow has already begun as 25 to 35 mph east to
northeasterly winds loft snow into the air from the preexisting
snow pack, leading to intermittent reductions in visibility.
Conditions will only worsen later today as the leading edge of
the front reaches Nunivak Island later this morning and the
Kuskokwim Delta coast & Western Capes this afternoon, when snow
begins to fall. For this threat, a series of Winter Weather
Advisories have been issued and are in effect through Sunday
morning. By Sunday, the front begins to weaken and move inland,
allowing snow intensities to decrease. This will combine with
temperatures rising to nearly 30 degrees, which should prevent
blowing snow from reducing visibility to as low as one half mile.

Out west, another low will track across the western Aleutians
into the Bering Sea, bringing a second round of rain and snow
pushing across the Aleutian Chain today. The low reaches the
northern Bering for Sunday, bringing in a round of reinforcing
snow for Southwest Alaska by Sunday night. Snow amounts may be
greater with this second round as model guidance indicates this
system is likely to be more moisture-rich than the first one. Snow
will begin to clear out from west to east on Monday as the low
sweeps across Southwest Alaska. Behind the front, colder air once
again returns to the Bering Sea, with several embedded shortwaves
leading to pockets of enhanced snow showers and gusty winds
trekking across the Sea and the Aleutian Chain.

CQ

&&

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

The upper level Bering low continues its Eastward trek into the
Interior through Friday. The upper level ridge decays along the
Canadian Border through the forecast period. Shortwaves rotating
through the pattern increase the changes in the flow. Confidence
is good with transient surface features bringing the most active
weather. There will be a brief respite from the Arctic air over
most of Interior with more marked changes across the South as the
trough pushes forward. A couple of North Pacific lows work their
way along the Aleutians and Alaska Peninsula to Southcentral
Alaska by Tuesday, with the second front approaching Friday. Gusty
winds and locally heavy snow changing to mixed snow and rain over
the Bering, and rain along the Aleutians and AKPEN, Kodiak Island
and on to the Southcentral Alaska coast. Snow will continue for
inland locations. The second Southern Alaska front brings a return
of colder temperatures to much of the state, spreading from North
to South over the Eastern Bering.

Further west, a well developed low and front approach the Western
Aleutians and Bering for Thursday and Friday. Widespread gusty
winds with areas of gale force gusts move over the Aleutians on
Friday. The next round of precipitation will be locally heavy.

Kutz

&&

.AVIATION...

PANC...VFR conditions will persist through the TAF period. Gusty
northerly winds are expected to slowly diminish through the day
today. By Sunday, winds will be light and variable.

&&