Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 011354
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
454 AM AKST Sun Dec 1 2019

.ANALYSIS AND UPPER LEVELS...

A vertically stacked low over eastern Siberia continues to steer
a broad trough northward through mainland Alaska. Rain and snow
showers persist over Southcentral behind this feature but have
diminished in intensity as the trough proceeds northward.
Meanwhile, a surface low over the eastern Aleutians/AKPEN is
quickly moving northeastward. The warm front associated with this
low has already initiated snow along the AKPEN and on Kodiak
Island. Precipitation will spread farther north along the front as
the day goes on.

&&

.MODEL DISCUSSION...

Model differences continue to make for a challenging snow
forecast over much of southern Alaska. Today, there`s still a fair
amount of uncertainty with snowfall amounts in interior Bristol
Bay. But, even given the wide range of possibilities, confidence
is decent there will be enough snow/wind/antecedent snow for
blowing snow to limit visibility at times, thus the Winter Weather
Advisory remains in effect. As for Southcentral, the challenge
rests on where the Gulf low sets up early Monday. See the
Southcentral discussion below for further information.

&&

.AVIATION...
PANC...Snow showers will bring vsby down at times this afternoon,
then snow will become steady tonight as a Gulf low approaches
Prince William Sound. By late tonight, expect steady snow at the
terminal to bring vsby down to LIFR.

&&

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

Unsettled weather is expected through Monday followed by drying
and cooler temperatures Monday night and Tuesday.

A triple point low forms near Kodiak Island this morning and
intensifies as it heads north to eastern Prince William
Sound/Central Gulf Coast tonight. This low then weakens and
retrogrades to the west some Monday morning before dropping south
Monday night. Light overrunning snow with weak warm advection in
advance of the low and associated front spreads north across
Southcentral today. Coastal areas will remain on the warm side,
so expect most sea level areas to remain as rain or mixed rain
and snow today. Things get a little more interesting tonight from
the Matanuska Valley to Cook Inlet. Unstable conditions spread
over these areas as strong cold air advection spills across the
relatively warm waters of Cook Inlet and the upper trough moves
across the region. It does not appear at this time that there will
be much of a moisture feed from Prince William Sound as the
surface low is fairly compact and too far south. That said, it
looks like the aforementioned ingredients will be enough to bring
accumulating snow across much of the Matanuska Valley to the
western Kenai Peninsula tonight through Monday evening. Snow
totals are still in question as models still differ on QPF amounts
and synoptic features. Stay tuned for updates.

Elsewhere, accumulating snow is expected across much of the
Copper River Basin tonight Monday. Gusty outflow winds are likely
across the eastern Kenai Peninsula tonight through Monday night.
Strong cold advection across the western Gulf will likely produce
NW storms across the Barren Island marine zones tonight and Monday
along with freezing spray potential. Tuesday bring quieter
weather.


&&

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

High pressure is firmly in control across most of Southwest
Alaska this morning, and this continues to shunt a developing
storm farther southward, to the point that it is now only going to
graze the Alaska Range and Alaska Peninsula with light snow. Snow
will move through by this evening as the low tracks into the Gulf
of Alaska this evening. Rather strong cold air advection and
increasing northerly/northwest winds will develop on the back side
of this low, and this will allow for favorable conditions for
blowing snow, mainly near Iliamna where the winds will be
strongest, and where the heaviest snow fell last storm. A winter
weather advisory for blowing snow remains in effect for those
conditions. Otherwise, expect mostly cold and dry conditions as
arctic high pressure settles in through Monday. The lone exception
will be snow shower chances along the coast Monday afternoon as a
weak trough and instability snow showers tracks into the
coastline.

&&

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

A gale force North Pacific low is tracking along the Alaska
Peninsula this morning and will quickly exit into the Gulf by
midday. Cold air advection and strong air/sea instability over the
Bering will take over, and this will support snow/rain squalls and
broad westerly near gale force winds as a series of mesolows moves
across the Bering Sea. A more substantial trough axis will merge
with a migratory North Pacific mesolow Monday and Monday night,
bringing enhanced gale force northwest winds and snow squalls to
portions of the Eastern Aleutians and Pribilof Islands. A gale
force warm front will begin working its way into the far western
Aleutians on Mon night.

&&

.MARINE...

A progressive pattern is expected this forecast period. On
Monday, low pressure will move into Prince William Sound with a
surface pressure of 974 mb to 977 mb. The Gulf Of Alaska can
expect gale force winds Monday and Tuesday. The low will slowly
decay and the pressure gradient forces which are responsible for
the wind intensity will decrease late Tuesday and Wednesday.

A mature front will push across the Central Aleutians and towards
the AKPEN which will produce small crafts and gales. In the wake
of this frontal passage another robust Kamchatka low will bring a
batch of unsettled weather to the Western Aleutians late Tuesday
and Wednesday. With this system expect another round of gale force
winds.

&&

.LONG TERM FORECAST...

The models are struggling in the long term forecast period but
there are a few key themes with the the global models. A. Its
highly progressive. B. There are 3 discernible fronts. By
Tuesday, the trough reaches the northern Gulf and expect this
feature to slowly begin to fill. To the west, there is another
front near the Aleutians supported by cold air over the Bering and
a strong jet core. A surface low near the central Aleutians will
continue to push eastward. A cold upper level trough swinging off
of the Kamchatka Peninsula Tuesday night and over the western
Aleutians Wednesday/Thursday will bring another batch of unsettled
weather to the region.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 161
MARINE...Gales: 119 120 132 137 138 150 155 411
Storms: 130 131

&&

$$

SYNOPSIS AND MODEL DISCUSSION...MM
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
MARINE/LONG TERM...SA


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