Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 190046
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
446 PM AKDT Sun Oct 18 2020

.ANALYSIS AND UPPER LEVELS...

An upper-level trough is lifting slowly north and east across
Southcentral this afternoon. Light snow continues to fall from
western Kenai Peninsula up through the Mat-Su Valleys and over
portions of the eastern Copper River Basin. Anywhere from a
dusting to close to 2 inches of snow has fallen through early-
afternoon from Kenai north to Anchorage, Palmer, and Wasilla.
Cold, dry air is lingering over the Copper River Basin where
temperatures this afternoon are struggling to climb out of the
teens.

Farther west, a ridge of high pressure is cresting over Bristol
Bay and the AKPEN. This feature has ushered in a more stable
airmass that has trapped low-level moisture at the surface,
resulting in widespread fog persisting along the Bristol Bay
coast this afternoon. Areas of freezing fog also remain as
temperatures from Dillingham to Togiak sit in the lower 30s.
Scattered rain/snow showers are falling over the Kuskokwim Delta
as a front over the eastern Bering advances toward the coast.

For the Bering/Aleutians, rain and southerly winds are occurring
along a front draped from east of the Pribilofs down to Unalaska.
Conditions over the western Bering/Aleutians are rather tranquil
with a general westerly wind and scattered clouds as a ridge
settles overhead.

&&

.MODEL DISCUSSION...

Models are in good synoptic agreement through the next several
days. Hi-res models were favored in the short term with regard
to the outflow wind event beginning tonight for eastern Kenai
Peninsula and Monday across coastal Prince William Sound.

&&

.AVIATION...

PANC...MVFR conditions are expected to continue through the
afternoon hours as light snow persists. Conditions should improve
this evening before IFR ceilings develop as low stratus and/or
fog moves over the airport complex early Monday morning.

&&

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

An upper level trough has made its way eastward over Southcentral
this afternoon bringing some light snowfall to the area. Flurries
may continue intermittently through the overnight hours, though
no additional accumulations are expected. As this trough shifts
to the east, the Copper River Basin will see about 1-2 inches
through the overnight hours with greater amounts at higher
elevations. Lingering low level moisture and a building ridge to
the west will allow for low level stratus and fog, especially
over Cook Inlet, Turnagain Arm, and the Knik Arm. This fog is
likely to linger through the morning hours Monday. By Monday
night, mid level winds are expected to shift to northerly,
bringing colder, drier air to the region. Additionally, a building
ridge to the west will amplify the pressure gradient, resulting
in gusty northerly to northwesterly winds, especially across the
northern Gulf coast, for Tuesday. Areas including Kamishak Bay and
the Barren Islands will see gusty northwesterly flow while
Valdez, Thompson Pass, and the Copper River Delta will see gusty
northerly flow through Wednesday.

&&

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

A disorganized upper level trough over Southwest today is expected
to move out of the region as a ridge builds in from the Bering.
At the surface, a north/south oriented front is expected to bring
precipitation to most of Southwest as it moves east through Monday
afternoon. Rain is likely over the lower elevations while snow is
more likely above 1000-1500ft and over the Middle Kuskokwim. By
Monday afternoon the front should dissipate; however, northwest
flow and residual weak upper level energy should allow for
rain/snow to continue over the Kilbuck Mountains, Middle Kuskokwim,
and western Alaska Range through Tuesday morning. On Tuesday,
the surface high is expected to be centered over the Y-K delta,
which will bring clearing skies and dry conditions to the
Southwest mainland through Wednesday. High temperatures may
increase marginally each day through the forecast period with
morning lows gradually decreasing as skies clear and allow for
radiational cooling. Unsettled weather is expected to return to
the AKPEN Wednesday morning as a strong front and north Pacific
low moves into the central Aleutians.

&&

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

Generally calm conditions are expected over the region through
Tuesday afternoon due to a ridge of high pressure over the
central Aleutians. The exception to this in the short term are
moderate winds through the gaps and passes of the AKPEN and
eastern Aleutian Islands due to a tight gradient between the
Bering high and a retreating trough over the Gulf of Alaska.
The main story will be a north Pacific low reaching the central
Aleutians Tuesday afternoon. Models are still struggling to
resolve the finer details of this system as there are multiple
potential areas of low pressure in the North Pacific at this time.
Regardless, there is strong model consensus of a gale force front
extending from Cold Bay to Atka by Wednesday morning. Mass
convergence along the eastern Aleutians and AKPEN may also
lead to storm force gusts along the Pacific side of the Aleutian
Chain. By Wednesday afternoon the low center should be near Adak,
so widespread gales and rain are likely over the central and
eastern Bering.

&&

.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:

A North Pacific low and front moves into the Central Bering by
Fri. Track and development of the system vary considerably, but
overall area coverage looks reasonable starting with widespread
Easterly small craft winds and waves with local gale force winds
spreading over the Aleutians and Alaska Peninsula. Conditions
continue as the winds wrap the low and affect most of the
Aleutians/Bering and the Alaska Peninsula through Fri.

&&

.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...Gale Warning 131.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...KO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CJ
MARINE/LONG TERM...MK/SS


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