Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 180148
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
448 PM AKST Fri Nov 17 2017

.ANALYSIS AND UPPER LEVELS...
There is a vertically stacked low over the northeast Gulf, with a
trough extending north into the Yukon Territory. There is also an
upper level ridge over the central Bering and central Aleutians.
There is an upper level low over northeast Russia. An associated
weather system is over the Kamchatka peninsula. The warm front
with this system is over the north central Bering, and the cold
front is over the western Bering and western Aleutians. Northerly
flow aloft is over southern Alaska, with a fairly strong offshore
gradient at the low levels. Some clouds and precipitation are
banked up against the northern and western slopes of the Alaska
range, and most of the remainder of southern Alaska is dry.

&&

.MODEL DISCUSSION...
The numerical models are in rather good agreement through the
short term portion of the forecast (Sunday afternoon). The models
seem to finally have a good handle on the developing triple point
low in the Gulf on Sunday, and then begin to diverge on Sunday
afternoon on the exact location of the surface low. Forecast
confidence is thus higher than normal.

&&

.AVIATION...
PANC...Overall, VFR conditions should persist through Saturday
evening. However, areas of fog are hovering just north of the
airport late Fri afternoon and may come in and out of the airport
through the evening. Increasing northerly winds are expected to
develop Friday evening and then persist into Saturday evening
which should clear out the remainder of the stratus as the mix
the atmosphere (though at first these winds may just push the
stratus into the airport at times this evening.)

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
Outflow winds along the North Gulf Coast will be the primary
concern tonight and Saturday as weak high pressure begins to move
into the mainland. This will leave a persistent pressure gradient
along the coast. The strongest winds of these should occur near
Seward, Whittier, and Valdez/Thompson Pass areas where gusty
outflow winds are expected to increase again this evening, then
begin to diminish on Saturday. The low stratus and fog that
developed in the Cook Inlet region yesterday behind the snow is
also beginning to slowly break up, however confidence is low that
this clearing will continue through the night. As a result it`s
possible that this layer may continue in spots into Saturday but
confidence in either solution is low.

The focus then shifts to the development of the triple point low
near Kodiak late Saturday night. The models are beginning to come
into better agreement with the track of this low somewhere in the
Central Gulf before descending into the North Pacific. The main
concern in the exact placement of this low is with Kodiak Island
and the potential for blowing snow, as previous runs of the GFS
kept the low just offshore, leaving the area under a persistent
band of snow with gusty northwesterly winds. Later runs however
are trending east with this low, leaving a bulk of the
precipitation and winds over the waters of the Gulf. Model trends
will need to be closely monitored, as trends back to the west will
result in significantly more snow/wind for Kodiak Island on
Sunday. This triple point low and its associated upper level
trough will also bring the next round of snowfall into
Southcentral for the day on Sunday, with widespread accumulations
expected with no downsloping present to protect the lee side of
the Chugach. This portion of the system bears watching as well as
guidance is hinting at the possibility for advisory level
snowfall, especially to the Kenai Peninsula along with the gusty
northerly winds.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Weak, cold, northerly flow will continue over southwest Alaska
until a warm front moves in over the area Saturday. The parent low
for this system will move over the Bering Strait Saturday
afternoon then rapidly intensify as it moves towards the Norton
Sound area. During this time its front will push across southwest
Alaska.

The front will be warm enough to change over some of the precip
along the southwest coast to rain, but the majority of southwest
Alaska will stay snow. This front will move slowly over interior
portions of southwest Alaska allowing enough time for snow totals
around 10 inches for areas from King Salmon north through the
Lower Kuskokwim Valley.

Meanwhile, strong cold air advection and favorable upper level
dynamics will allow for strong winds along the Kuskokwim Delta
coast early Saturday morning. These winds will last into Sunday
afternoon before tapering off as the main low drifts south into
the Gulf.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
High pressure over the southern Bering is retreating into the
North Pacific which will make way for a front to push through the
eastern Bering and Alaska Peninsula from the low moving towards
Norton Sound. A favorable jet position, cold air advection and
other upper level dynamics will bring strong winds to areas all
around the eastern Bering.

The first to see these winds will be the Pribilof Islands which
will amp up Saturday night and last into Sunday afternoon. The
front will then push south bringing strong winds to the Eastern
Aleutians and Alaska Peninsula early Sunday morning. Strong winds
for these locations will last into Sunday evening before
diminishing. Winds for all three locations have the potential to
reach warning level.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Expect near to below normal temperatures with periodic snow across
the southwest, and periodic cloudiness for Southcentral Alaska.
Gap winds will pulse up with every exiting disturbance.

Monday evening begins day 3 with a system exiting the Gulf of
Alaska. Dry conditions will take hold over much of southern Alaska
within an outflow pattern, mainly along the north Gulf coast.
Overall, the upper level pattern remains very progressive with
strong, discrete disturbances propagating from the northwest
Pacific into the Bering Sea. Each of these systems will send a
surface low pressure east of Kamchatka while sending a front from
west to east across the Bering. However, troughing from northwest
Canada southward will turn the storm track from the Bering into
the Gulf of Alaska. As far as sensible weather is concerned, the
periodic fronts will push snow onto the mainland while the front
falls apart as it moves west to east.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 195.
 High Wind Watch 155 181 185.
 Winter Weather Advisory 152 161.

MARINE...Gale 127 128 130-132 138 150-175 180.
 Storm 179 181 185.

&&
$$

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



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