Small Craft Advisory 791, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
521 AM AKDT Mon Oct 19 2020

.ANALYSIS AND UPPER LEVELS...

An upper level trough across Southcentral continues to work its
way eastward this morning, clearing out the moisture and snow
showers that were observed yesterday. As this feature moves out of
the region, low stratus and fog have developed across areas of
Southcentral this morning.

Above freezing temperatures across Southwest Alaska is keeping a
few rain showers stretched from Bethel to interior Bristol Bay and
the Alaska Peninsula as an upper level wave keeps active weather
for the region. Farther west, quiet conditions are set up across
the Bering and Aleutian Chain with a ridge of high pressure
building in.

&&

.MODEL DISCUSSION...

Models are in good synoptic agreement over the next few days. The
hi-res models were favored in the short term with regard to the
outflow wind across the eastern Kenai Peninsula and across
coastal Prince William Sound today.

&&

.AVIATION...

PANC...IFR conditions could develop early this morning with low
stratus and/or fog moving into the area. Conditions should improve
late this afternoon and evening, but will likely drop back to
MVFR during the evening hours.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (through Tuesday night)...

A weakening frontal trough extending south across the Copper
River Basin will continue areas of light snow across the Basin
today followed by drying tonight with increased offshore flow.
Further west, stratus and fog from Cook Inlet to over the MAT-SU
will dissipate some today. However, it will likely return again
tonight.

A combination of low level cold advection, an inverted surface
trough over the Northern Gulf, and upper waves dropping south
across the eastern Mainland/Gulf, will give rise to strengthening
outflow and gap winds through Tuesday night. The strongest winds
will likely be from the Eastern Kenai Peninsula to along the North
Gulf Coast.

&&

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

Residual light showers linger into tonight as a weak upper level
wave gets pushed out by a building ridge over the Central Bering.
Showers should remain as rain, with periods of light snow for the
parts of the Kuskokwim Valley and higher elevations.
Additionally, a band of fog/low stratus is tracking across
Southwest throughout the morning ahead of the wave. The surface
high pushes northeast across the Bering towards the Y-K Delta today,
forcing the ridge onshore by tomorrow. Thus, clearing skies and
drier conditions are expected Tuesday and Wednesday. Flow becomes
more northerly ahead of the ridge as well. This inflow of colder
air from the interior combined with radiational cooling from
clearer skies will further lower overnight temperatures Tuesday
and Wednesday night.

A strong front attached to a surface low in the North Pacific
approaches the Southwest coast by Wednesday. Expect the transition
back to unsettled weather by the end of next week.

&&

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

A surface high and associated ridge build over the Central
Aleutians this morning and track northeast over the next couple
days. Conditions overall should remain relatively calm through
tomorrow until a front off a surface low in the North Pacific
approaches the Central Aleutians. Widespread gales are expected
to move with this front Wednesday and Thursday. Periods of storm
force winds are included, as models have started coming into
better agreement, though this still holds a level of uncertainty.
Moderate to heavy rain along the Southern AKPEN and Central
Aleutians are also expected to accompany this front.

&&

.MARINE (Days 3 through 5: Wednesday through Friday)...

Gulf of Alaska:

Generally light winds over the Gulf yield to a front that will
stretch across the Gulf through Fri. Forecast models track and
development vary considerably through the period, but favor
widespread Easterly gale force winds and waves spreading over the
Gulf through Fri. The gales retreat into the Western Gulf by Fri,
leaving widespread small craft winds through Fri. Gusty Easterly
winds will affect the North Coast areas.

Bering Sea:

Models are increasing in confidence with a North Pacific low
moving across the central Aleutians and Bering on Wednesday. This
system should strengthen and see embedded storm force winds as it
lifts northward through the day on through Thursday for the
eastern Bering and AKPEN. A second North Pacific low moves
towards the western/central Aleutians late Wednesday into
Thursday, but models are struggling with the strength and track
of this second system through Thursday morning. However, models
agree that this low system will track into the Bering by Friday,
keeping an active weather pattern and strong winds through the
end of the week.

&&

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

We've been tracking an upper level low that is slowly drifting
across northern Siberia this weekend. An amplifying shortwave
trough can be seen across Mongolia Sunday afternoon and will be
the focus for weather late into next week. This shortwave will
dive south, interact with the north Pacific jet and deepen the
upper level low that it is accompanying. By late Wednesday we
expect this feature to detach from the parent trough and become a
closed low south of Dutch Harbor. Another shortwave riding the
exiting jet will help to lift the low into the eastern Bering
through the weekend. Working east ahead of this system is a
transient upper level ridge that be over western Alaska Thursday,
southcentral Friday and into Canada on Saturday. With this ridge
will be minimal winds accompanied by clearing skies and colder
(overnight) temperatures. Overall confidence in the long range
forecast is beginning to increase considerably over the last few
days. Operational and ensemble guidance is coming into much
better agreement with handling of all of these features. The
primary ticket is that the aforementioned low will slide up into
the Bering (in previous days, guidance indicated a quick erosion
of the ridge, with a quick movement over the mainland). On Friday,
the Aleutians will see a surface low lift into the Bering within
the Adak vicinity, driving a weather front across the eastern
Aleutians. By the weekend, the front will slide over Kodiak and
along the Gulf coast. While early indications are that we'll warm
some and have cloudier skies, it's still too far out to tell
whether the front will bring any rain/snow to the Anchorage area.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ALH
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
MARINE/LONG TERM...MK/SS/ALH