Small Craft Advisory 871, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
529 AM AKDT Thu Nov 3 2022

.ANALYSIS AND UPPER LEVELS...

A large vertically stacked low is moving slowly east-southeast
across interior Southwest Alaska this morning. Northerly winds
along the coast remain gusty, but will continue to be on a
downward trend as the low moves farther inland today. Downstream
of the main low, a triple-point low located southeast of Prince
William Sound continues to track south-southeast across the Gulf.
Strong southeasterly flow and a deep fetch of moisture continues
to produce a widespread area of precipitation from the northern
Gulf and Southcentral coast to Cook Inlet and the Susitna Valley.
As such, a Winter Weather Advisory for the Anchorage area with
locally higher amounts for the Anchorage Hillside and Eagle
River, is still in effect until 10 PM AKDT today. Farther west,
another shortwave trough is dropping south across the Bering,
helping to maintain shower activity and further enhance the surge
of colder air moving southward.

&&

.MODEL DISCUSSION...

Models remain in good synoptic agreement overall through the
short term. The biggest challenge in the short term will be the
extent of light snow across the Anchorage Bowl and Matanuska
Valley through Thursday afternoon. Models have come into better
agreement on the strength and placement of the main upper-level
low. Therefore, more confidence is had in the forecast of the
subsequent snow bands following the current system set up.

&&

.AVIATION...
PANC...Snow is expected to continue over the terminal this morning.
Expect MVFR conditions to drop to IFR in steadier snow. There is
a possibility that visibility could briefly drop to LIFR in any
heavier snowfall early this morning. Southerly winds will shift
north-northeast early this morning with gusty winds over the
terminal this afternoon. Snow will slowly begin to taper off later
this evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 to 2: Today through
Friday Night)...

An upper level low is slowing moving across the Kenai Peninsula
and towards the northern Gulf this afternoon. This reflects down
to surface as a low over the northern Gulf. This feature is
producing bands of snow across from the northern Kenai Peninsula
and towards Anchorage and the MATSU valleys and will produce several
more inches of snow across parts of the area with the highest
amounts along the hillsides of Eagle River and Anchorage and the
Chugach Mountains. Upslope flow will develop by this afternoon as
another shortwave trough swings southward enhancing snow across
the hillsides and Chugach Mountains. A Winter Weather Advisory is
in effect until 10 PM this evening for the Anchorage area, Eagle
River, Chugiak, Peters Creek and the Glenn Highway from the Knik
River to Anchorage. Expect another 3 to 5 inches across Anchorage,
Chugiak and Peters Creek and 5 to 9 inches along the Anchorage
Hillside and Eagle River. The MATSU valleys will get more snow
today with up to 4 inches expected. By late tonight near midnight
the snow will end across the populated areas with lingering light
snow over the higher terrain through Friday morning. As the low
pushes east on Thursday night and Friday north and westerly gap
winds will develop and strengthen as cold air advection moves
across the area. This will create very strong winds across Kodiak
Island, the Barren Islands, Seward and Resurrection Bay, Whittier
and Passage Canal, and the Valdez area and adjacent coastal
waters. Winds are expected to stay below warning criteria through
Friday, but could get near warning levels around Kodiak island
Friday night into Saturday as cold air is reinforced by another
shortwave

&&

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

Clear and cold conditions are expected across most of Southwest
today as surface high pressure nudges in from the west. Broad
northwesterly flow will continue to advect cold Arctic air over
the region, and region-wide daytime temperatures will linger
around 15 to 20 degrees today. Gusty northerly gale-force winds
are also expected to develop late today along the south side of
the Alaska Peninsula as a result of the cold surge.

Chances for snow showers increase by Friday morning as a
upper-level shortwave and surface low enter the Kuskokwim Delta
from the northwest. Light snow will spread southeast through the
rest of the day and taper off by late Friday night. Most locations
near sea level are expected to see around 1 to 2 inches of snow
while locations in or near the Kuskokwim Mountains can anticipate
higher amounts. Gusty gale-force winds along the backside of the
low may result in brief periods of reduced visibilities due to
blowing snow for the western Kuskokwim Delta on Friday morning. As
the shortwave exits into the Western Gulf, increased cold air
advection will lead to another round of strong, gusty
northwesterly gap winds across Bristol Bay and the south side of
the Alaska Peninsula. The stronger winds are expected to increase
by Friday night and will persist through Saturday, with gusts to
storm force possible out of the Alaska Peninsula gaps.

Also on Saturday, an upper-level ridge of high pressure from the
Bering will build eastward across Southwest Alaska. As a result,
cold and dry conditions will persist across the region through the
weekend before the next system arrives.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 3: Today
through Saturday)...

Persistent northwesterly flow and drier conditions are expected to
continue today and through most of Friday as high pressure
blankets the region. A front will approach the Western Bering
starting later on Friday, but rain is not expected to spread
across the Western Bering and Aleutians until Saturday morning.
Southerly gale-force winds will accompany this system and will
mainly stay confined to the western-most region of the domain.
Rain and winds with this system will gradually taper off through
the rest of Saturday. A North Pacific low is forecasted to reach
the Central Aleutians late Saturday and then continue northward
into the Bering. Precipitation with this low is also expected to
remain as rain.

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

Ensemble guidance is in excellent agreement in the longwave
pattern that a high amplitude ridge and omega block will exist
over the Alaska Mainland on Sunday. The ridge axis is expected to
be over central to western Alaska, which will place the Bering Sea
and Southwest in an active, warmer, and wetter pattern while
Southcentral will stay clearer and colder, though a slight warming
trend is expected through Wednesday. Models often struggle on the
breakdown of these ridges and tend to break them down faster than
what occurs. This will lead to some uncertainty in the long term,
particularly for how far east precipitation is able to make it
into Southcentral. Most deterministic and ensemble solutions
indicate a North Pacific low will cross over the Aleutians on
Sunday and travel north into the Chukchi Sea by Wednesday. This
storm track will send a slug of warmer air into Southwest Alaska,
which will likely result in rain along the coast and freezing rain
and snow for interior areas late Sunday into Monday.
Deterministic try to form a low along the system's front near
Kodiak Island, but how far north and east this system is able to
travel remains uncertain due to ridging. It's most likely that
this will bring precipitation to coastal areas before the system
is deflected south by the strong area of high pressure. In
summary, the Bering Sea and Southwest Alaska is looking to be
warmer and wetter, while Southcentral will remain colder and
drier.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 101.
MARINE...Storm Warning: 130-131, 351-352.
 		 Gale Warning: 119-121, 125, 127-129, 132, 136-139, 150, 155,
 				       160, 165, 178, 180-181, 185, 411, 414.
FIRE WEATHER...NONE.

&&

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