Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 171304
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
404 AM AKST Tue Jan 17 2017

.ANALYSIS AND UPPER LEVELS...
A remnant low remains in Prince William Sound following the front
which lifted through Southcentral Alaska yesterday afternoon and
evening. A trough trails into the western Gulf with southwesterly
flow out ahead of it continuing to push snow showers onshore along
the northern Gulf Coast. Behind the trough, drier northwesterly
flow has been diminishing snow showers however, this is being
offset somewhat by cold advection increasing instability. Over
mainland southwest Alaska, very cold temperatures persist under a
cold upper level trough. Cold air/instability snow showers
continue over much of the Bering while a surface low begins to
develop near Adak.

&&

.MODEL DISCUSSION...
Models remain in good agreement through midweek with respect to
offshore flow developing in the Gulf of Alaska and southern
Mainland Alaska, however struggle significantly with the low
developing over the Central Aleutians and tracking into the
Bering. For the western domain a blend of the NAM and Canadian was
preferred while for the east the NAM and GFS were preferred to
better capture outflow winds.

&&

.AVIATION...
PANC...MVFR conditions with occasional snow showers will taper off
this morning improving to VFR as the flow shifts to drier
northwesterly. VFR conditions will persist into Wed.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The upper level trough over Southcentral Alaska will move east of
the area this afternoon. Showers will linger over some areas,
especially near Prince William Sound and the Gulf coast east of
the Sound with plenty of low level moisture streaming in. The main
story for the next couple of days will be the intrusion of very
cold air. Cold advection is already beginning, and most areas will
see steadily dropping temperatures through today and tonight. On
Wednesday night most locations will see temperatures lower than
they have seen in several years. Very cold wind chills are
expected through Broad Pass beginning later today as cold air
pours in from the north.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA...
Cold and dry conditions for southwest Alaska will continue into
Wednesday when a front from a low in the Bering will push in over
the area. The front looks to bring light snow and cloud cover to
the area as well as raise temperatures. However, temperatures
will still stay well below freezing.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
The big question for the Bering and Aleutians is what will happen
with the low near the Central Aleutians. Models have come into
agreement that the low will track into the Bering and move toward
the Pribilof Islands today into Wednesday, but they are struggling
with how fast the low will move through and where it will go
afterward. The majority move it toward the Eastern Aleutians
Thursday and that is the higher confidence forecast. The toughest
question is how much snow will fall for the Pribilof Islands
Wednesday and how much blowing snow the area will see. There is
decent agreement with the winds, but current guidance has the
heaviest snow missing the islands, reducing the blowing snow
threat of visibility dropping below one mile.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Beginning the extended period forecast Wednesday night, a very
deep arctic trough will be centered over the central part of the
state with the trough axis extending through Southern Alaska.
Strong offshore flow will be in place across the North Gulf Coast.
This pattern will be supporting 850C temperatures in the range of
-20C across Southcentral to -30C across Southwest Alaska. These
cold temperatures will settle in through Friday morning before
warmer air moves back in as a Bering low spreads clouds and warmer
air northward. This will increase snow chances for all of Southern
Alaska, although at this juncture the overall pattern does not
look very conducive to any significant storms. Temperatures will
moderate through the remainder of the weekend into the next week
as a series of weak Gulf lows linger near the Gulf coast, keeping
enough clouds and warm air advection aloft to keep bitterly cold
temperatures from settling into Southcentral.

Over the Bering Sea, a strong gale force low will be moving from
the Eastern Bering Sea into the Gulf of Alaska Thursday and
Thursday night. Strong cyclonic flow behind this low will keep
widespread snow showers and northerly winds over the Bering Sea
through Friday before a strong low potentially moves into the
Western Bering Sea later in the weekend into next week.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory...145.
MARINE...Heavy Freezing Spray Warning 121 126 127 129 130 138 139
  141 150 160 165 180 185.
         Gale Warning 130 131 132 170 173 174 175 177 179.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...JER
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...JA


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