Small Craft Advisory 861, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
443 PM AKST Wed Nov 11 2020

.ANALYSIS AND UPPER LEVELS...
The dominate feature today is a stacked upper low and surface low
near Kuskokwim Bay and a trailing frontal trough extending across
western Alaska to over Southcentral. Showers, mostly rain, were
observed over Southwest Alaska and across the Aleutians, Bering
Sea, and AK Pen. Strong west to northwest winds (gale to storm
force) on the backside of the surface low were evident over the
eastern Bering Sea/Aleutians, and the Ak Pen. Gusts observed along
the Alaska Peninsula were in the mid 50 kt range. A fairly well
defined surface low was observed moving north over Cook Inlet this
afternoon. Rain showers were observed across the Kenai Peninsula
to the Northern Gulf with mixed precipitation to snow to the
north.

&&

.MODEL DISCUSSION...
Models through the short term are in fairly good agreement.

&&

.AVIATION...
PANC...Generally MVFR visibilities and/or ceilings are expected
through tonight.

&&

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

An upper level trough from Southwest Alaska extends eastward to
Kenai Peninsula through the northern Gulf, and models are moving
this feature northward toward Alaska Bowl tonight. Cold advection
from the north of Matanuska Valley combined with the onset of the
shortwave approaching Anchorage Bowl will increase the chances of
snow over Matanuska Valley tonight. Meanwhile, southeasterly winds
advecting warm temperatures over Anchorage Bowl could provide mix
rain/snow, and increased winds reaching up to 30 mph along the
Turnagain Arm and higher elevations could yield to a chance of
freezing rain this evening.

As the upper low from SW Alaska treks toward Kenai Peninsula and
the western Gulf tonight into Thursday morning, the chance of snow
will potentially increase over much of Southcentral Alaska and
parts of Kodiak Island in the next couple days. Moisture combined
with warm air advection over the Gulf will trigger isolated
thunderstorms south of Seward and over the northern Gulf this
evening. Overall, snow showers will persist over the region
through Friday, with strong winds expected over Kodiak through at
least Thursday night.

&&

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

A broad upper level trough with multiple embedded lows persists
across the state. One weakening low tracks across the Southwest
towards Bristol Bay today before exiting the region tomorrow. With
it comes some showery precipitation, mostly in the form of a
rain/snow mix for tonight and will transition to snow by tomorrow
as flow becomes northwesterly and colder air is advected in. A
second surface low forms just north of the Y-K Delta by Friday. A
shortwave trough extending off of this low pushes south across the
Bering towards the southern AKPEN. Models show the low itself
begin to travel south across the mainland by Friday evening, but
diverge on timing. Precipitation will remain light Friday into
Friday evening, and the Southwest should see relatively drier
conditions by Saturday.

&&

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

Primarily westerly flow across the Bering through tomorrow as a
weakening front reaches the Southwest coast. Mostly diminished
winds, except for some gales along the Southwest coast and storm
force winds in Bristol Bay through tonight. A second front
approaches from the north and will track across the Bering towards
the Southern AKPEN through Saturday. Flow transitions to
north/northwesterly behind the front and will include significant
cold air advection. By Saturday, a ridge begins to form over the
Western Bering, but will likely be short-lived as a low currently
over Russia approaches the Western Aleutians.

&&

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

Gulf of Alaska:

A series of weak low centers moves across the Northern Gulf
through Mon. The track and development of these lows are mixed,
but confidence is good for easterly winds along the North Gulf
Coast and westerly winds over the Southern Gulf, gustiest near
Kodiak Island Sat. A polar front crosses the Alaska Peninsula Sun
with increasing confidence for widespread northwesterly small
craft winds and waves to extend from the Shumagin Islands to the
Barren Island and Kachemak Bay into the Gulf, with local gale
force winds near Kodiak Island through Mon.

Bering Sea:

A polar front crosses the Aleutians and Alaska Peninsula for Sun.
Widespread northerly small craft winds and waves over the Central
and Eastern Bering exit Bristol Bay Sun night. Local gale force
winds with the front across the Central Aleutians through Sat
night. A well developed front approaches the Western Aleutians and
Bering Sun. The track and development of the front are mixed, but
confidence is good for widespread high-end southerly gale force
winds and waves with local storm force wind gusts moving to the
Central Bering by Mon.

&&

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

The long term forecast begins Sunday with the highly amplified
ridge over the Aleutians shifting east in response to a storm
system developing off the coast of Russia. This eastward shift
will help relax the cold, northerly flow across the
Bering/Aleutians with snow showers and gap winds over the AKPEN
both diminishing. This ridge will extend north and east over the
Southern Mainland by Monday, resulting in a continuation of mainly
clear and dry conditions (with the exception of isolated high
elevation snow showers) and gusty, northerly gap winds along the
Southcentral coast.

By Monday, the GFS and EC diverge in their respective solutions.
The EC drops a shortwave southeast from the Bering Strait across
interior Alaska. This solution would result in a weaker ridge
building over Southcentral and keep a higher chance for snow
showers in the forecast, especially along the Alaska Range
through Tuesday. With the ridge not as robust, the EC also brings
the front associated with the aforementioned low to Southwest
Alaska for Tuesday. The GFS, on the other hand, keeps a stronger
ridge in place while slowing and weakening the front as it moves
across the Bering. The GFS finally brings a weaker front to the
Southwest coast by Wednesday, with both long-term models
dissolving the front while keeping the ridge steadfast over the
Al-Can border. Also by Wednesday, both models have the entire
upper-level trough moving over the Bering with unsettled weather
continuing through mid-week for the Bering and Aleutians. As for
the Southern Mainland, it looks like clear and dry conditions will
prevail, especially for Southcentral where the northerly flow
will persist.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 130-132 138 160 150 155 170 171 177 179 181
185 351 352 412-414.
Storm Warning 160 165180.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
MARINE/LONG TERM...MK/TM