Area Forecast Discussion
Issued by NWS Anchorage, AK

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203
FXAK68 PAFC 201322
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
422 AM AKST Mon Jan 20 2020

.ANALYSIS AND UPPER LEVELS...

A broad upper level low is currently centered over Siberia. Its
associated negatively tilted trough axis extends southeastward
through the Alaska Peninsula. A surface low over the northern
Bering is leading to scattered snow showers across much of the
Bering/Aleutians, while Southwest Alaska remains quiet under weak
flow. Farther east, a ~986 mb low is tracking northwestward near
Resurrection Bay and is bringing significant snowfall to the
Portage Valley. Snow tapers off to the west, however latest radar
returns show precipitation reaching as far as Cook Inlet.
Widespread snow is also continuing over Prince William Sound.

&&

.MODEL DISCUSSION...

Current radar/satellite shows the aforementioned low trending
towards the northerly solutions as expected. Per the usual in
these setups, snowfall totals remain the greatest challenge,
particularly over Anchorage. Some high-res models snow several
inches, while others snow almost nothing. Thus confidence is high
regarding the overall synoptics of this system, but low with
regards to its mesoscale aspects.

&&

.AVIATION...

PANC...Snow showers will persist through tonight. All flight
categories between IFR and VFR, as a result of intermittent
reduced visibilities and/or ceiling heights, are likely through
this time period (with none of them expected to persist for more
than a couple consecutive hours). VFR conditions are expected to
prevail Tuesday morning as the associated low weakens. Light and
variable winds will continue.

&&

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

The surface low just south of the Kenai Peninsula will slowly
move north today as an upper level trough associated with a large
low over the northwest Bering moves into the area from the
southwest. Snow is expected for areas from the north Gulf coast
through the Kenai Peninsula and upper Cook Inlet today. Some rain
is possible from Cordova through Prince William Sound as the air mass
is fairly warm. Temperatures for inland areas will also warm up.
Precipitation will then taper off tonight through Tuesday night as
the upper low tracks through Southcentral and ushers in a drier
air mass. Colder temperatures will also begin to move into the
area Tuesday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (through Wednesday)...

A weak front continues to approach the Southwest coast, bringing
scattered snow showers to the Kuskokwim Delta area this morning.
As the upper level trough moves inland, expect the front to
produce some scattered snow showers across coastal areas of
Southwest throughout the day today before dissipating by tonight.
Some low level stratus and areas of patchy fog are possible along
the coast this morning as well. By Tuesday, a cold Arctic air mass
will arrive from the northwest, allowing colder temperatures to
persist through the week. Conditions should generally trend toward
clearing by Wednesday as a ridge of high pressure over the Bering
slowly tracks eastward toward Southwest.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (through Wednesday)...

A showery pattern remains in place across the Bering as a trough
in the northern Bering slowly moves eastward. The Pribilof Islands
will see intermittent snow showers through Tuesday. A low centered
south of the Aleutian Chain has allowed for increased cloud cover across
the western Aleutians. This low will remain south of the Chain as
it tracks eastward through Tuesday. By midweek, the next front
arrives over the western Aleutians bringing warmer southeasterly
flow. The overall pattern will become more amplified across the
Bering as a gale force low moves into the western Bering and
encounters a blocking ridge in the eastern Bering.

&&

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

Gulf of Alaska:

After quiet weather across the Gulf on Wednesday, a low moving
into the eastern Gulf will bring the threat of north to
northwesterly gales through the Barren Islands and south of Kodiak
Island. There is some disagreement in the track of the low, but a
westerly track and stronger low could result in storm force winds
in those same areas, primarily Thursday night into Friday morning.
Gales will continue through the day Friday.

Bering Sea and Aleutians:

A strong low meandering south of the western Aleutians is expected
to produce easterly gale force winds, with intermittent storm
force winds possible, for all three days across all of the western
and central Aleutians and adjacent waters. Where the strongest
winds set up will be determined by the exact track of the low and
associated fronts. Strengthening high pressure over the northern
Bering will also produce gale force outflow winds through the
eastern Aleutians, Alaska Peninsula, and near Cape Newenham. The
strongest winds in these areas are expected Friday.

&&

.LONG TERM FORECAST (Days 3 through 7: Wednesday through Sunday)...

A stagnant, slow-to-change weather pattern is expected to set up
across Alaska and the Bering Sea throughout the entire long-term
forecast period. A stalled out low is expected to set up south of
the western Aleutians, it`s northern periphery will cause strong
winds and rain across the central and western Aleutians from
Wednesday right through Sunday. Any fronts associated with the low
may briefly increase both the winds and the precipitation
intensity. Moving east from there, an area of high pressure over
the Pribilofs Wednesday morning will move over the west coast of
Alaska and intensify with time through the weekend. This will have
several effects: first, it will allow an Arctic air mass to
reestablish itself across much of mainland Alaska from Friday
through the weekend, resulting in an other round of well-below
normal-temperatures across all of Southern mainland Alaska.
Second, it will cause gusty winds to develop, especially through
the mountain gaps such as Thompson Pass, the Seward area, the
Barren Islands, and south of Kodiak Island. The combination of
falling temperatures and gusty winds will almost certainly cause a
renewed round of wind chill concerns, both in Southwest and
Southcentral. The cold and gusty outflow winds currently appear
to the strong enough around the Anchorage area that freezing fog
concerns appear unlikely.

The last and certainly most uncertain element to the long term
forecast will be the tracks of a series of lows that are expected
to move through the Gulf through the long-term period. All of the
models agree that lows will move through the Gulf, so it`s highly
likely that unsettled weather will be the norm across coastal
areas. The lows will each have the potential to produce snow for
coastal communities, spread some cloud cover inland at times,
which will make the temperature forecast more difficult, and
increase the winds through the gaps even further, adding both to
the wind chill concerns and possibly localized blizzards where the
strong winds and heavier snow could combine. Thus, despite an
otherwise stagnant weather pattern, the forecast will remain
challenging and active, especially for Southcentral.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 127.
         Heavy Freezing Spray Warning: 185.
FIRE WEATHER...NONE.

&&

$$

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



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