Small Craft Advisory 879, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
357 PM AKST Mon Nov 16 2020

.ANALYSIS AND UPPER LEVELS...
A amplified upper ridge extends north across Western Alaska. With
the exception of some cirrus over the Kuskokwim Delta and patchy
low clouds over Knik Arm and the Copper River Basin, fair skies
prevailed across much of the Southern Mainland. Surface ridging
over the Mainland and lower pressure over the Gulf gave rise to
locally gusty outflow winds from the North Gulf Coast to the
Western Kenai Peninsula. A weakening 980s gale force surface low
was observed just north of the Central Aleutians this morning. Its
associated occluded front extended over the eastern Bering Sea,
through the Eastern Aleutians, and to a triple point well south
of the Aleutians.

&&

.MODEL DISCUSSION (through Thursday afternoon)...
Models are in good agreement across Southcentral with outflow/gap
winds the main weather impact for the region. Will be leaning
toward the HI-RES models and hand edits.

The pattern is fairly active out west over the Bering
Sea/Aleutians through Thursday afternoon. Models overall are in
good agreement with the next storm that will move into the
western Bering Sea Tuesday. The next storm system after that
point, which moves east along the Aleutians Wednesday night and
to the eastern Bering Sea Thursday, is still a point of
contention between the models. The good news is that the GFS/ECMWF
have come into much better agreement, so confidence of storm force
winds with this system has increased.

&&

.AVIATION...
PANC...VFR conditions are expected through this evening. IFR
conditions are possible with areas of fog during the overnight and
morning hours Tuesday. Light winds will prevail.

&&

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

An approaching upper level ridge combined with northerly surface
flow will continue to bring clear skies and colder temperatures to
Southcentral through mid-week. Patchy fog is possible overnight
tonight into Tuesday morning near Knik Arm. If this becomes more
widespread, low temperatures may not fall as much as forecast.
Offshore flow will gradually increase Tuesday as a low tracks
northward along the Panhandle, increasing the pressure gradient
along the coast. Moreover, the aforementioned ridge will continue
to track eastward, and this will cause mid to upper winds to
becoming more aligned with the surface flow. As such, gusts
across Thompson Pass, Valdez and the Copper River Delta could
approach 60 mph Tuesday night into Wednesday. Other areas such as
Whittier and Seward will likewise see gusty winds, although these
are not expected to be as strong. A low will move near Kodiak
Island by Thursday morning, bringing the potential for rain/snow
by that time.

&&

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

There is a dome of high pressure over the interior that continues
to impact SW AK. Expect dry conditions for another day except for
Nunivak Island and Nightmute through Hooper Bay. In satellite
imagery and on several webcams, cirrus in advance of a front is
already present for some locations in SW AK. Wednesday, light
showers will impact the coastal communities, but the moisture
will not reach the interior SW AK on Wednesday. Thursday, the
chances for showers increase, and the thermodynamics suggest any
moisture that reaches the ground will fall as snow. There might be
a few tricky places like King Salmon, Togiak and Hooper Bay, but
generally expecting light snow on Thursday.

&&

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

A parade of lows will impact the region. A low north of Atka
will move towards the Pribilofs tonight and continue to fill.
As a result, the winds associated with this system will weaken.
Tuesday, this low will be over St Matthew Island. The low's
remnants will become absorbed into the longwave pattern Tuesday
night.

The next storm system to move in is already near Attu Island
today. This low will deepen and move towards Kamchatka. Cold air
will get wrapped into this system and gale force winds will
materialize. The associated cold front will impact the western
Bering/Aleutians early Tuesday. Late Tuesday/Tuesday night, this
front moves into the central Bering. By 12z Wednesday, the models
have the anchoring low at an intensity ranging from 954 mb to 959
mb.

On Wednesday, a new low will move out of the North Pacific and
towards Adak. The models have been waffling a bit with this
system, but the Aleutians can anticipate more windy and wet
weather. The surface low should be between Dutch Harbor and St
George Island on Thursday.

&&

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

Gulf of Alaska:

A low in the southeastern Gulf will produce gap winds along the
northern Gulf coast through early Thursday morning. Another low
arrives over the western Gulf Thursday afternoon bringing small
craft level winds with gale force winds likely through narrow,
channeled terrain, including over Kamishak Gap and the Barren
Islands. By Friday morning, a storm force low approaches the
western Gulf, spreading in gales and storm force winds over Gulf
waters through Saturday.

Bering Sea:

There is increasing confidence that a storm force low in the North
Pacific will lift northward into the Bering by Thursday. This
storm force low is expected to track northward into the northern
Bering Friday evening. A second gale force low forms on the heels
of the first and tracks northward over the Bristol Bay area. There
is lower confidence in the strength and track of this second
system, although storm force winds are possible. A third low
arrives late Saturday that introduces a potential for gale force
winds, but confidence is extremely low at this time given
extensive model discrepancies.

&&

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

The long term begins with a highly amplified pattern as a deep
upper level trough over the Bering remains in place. Meanwhile, an
upper level ridge builds over the mainland. As the upper level
trough ejects shortwaves eastward, this pattern will support a
series of surface lows developing near the Alaska Peninsula area
and tracking eastward into the Gulf. By the weekend, the ridge
retreats to the north allowing for the formation of a broad upper
level trough that should persist over the mainland through Sunday
night. By Monday, the active pattern continues over the western
Bering as there is growing model consensus that a strengthening
low will enter the western Bering Monday afternoon.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning: 178,411.
Gale Warning: 127,128,174-177,179,185,412-414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RMC
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
MARINE/LONG TERM...KO