Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 281440
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
540 AM AKST Tue Jan 28 2020

.ANALYSIS AND UPPER LEVELS...

On satellite imagery there is a mature low in the North Pacific
with a well defined occluded front south of Cold Bay and the
AKPEN. There is a 180+ knot jet core south of the Aleutians.
Meanwhile the remnants of a decaying low are over the Eastern Gulf
and moving inland. Persistent northerly flow continues over
southwest Alaska which is steering arctic air into the region
resulting in dangerously low wind chills over southwest Alaska.
Strong northerly gap winds with cold advection were also observed
through the gaps in the Alaska Peninsula.

&&

.MODEL DISCUSSION...
Models are in decent agreement with the longwave pattern. The past
72 hrs, there has been consistent divergence early in the
forecast period and that trend continues for both the North
Pacific and the Gulf Of Alaska with the latest run of the models.
Confidence is high that the potent low in the North Pacific will
deepen an additional 10 millibars today as it moves into the Gulf
Of Alaska. However, the precise track of the surface low has not
been locked on yet.

&&

.AVIATION...
PANC...VFR conditions expected at the onset of the TAF period.
Mid-level clouds have worked their way into the region and on the
7z metar a layer was observed at 5,000 ft. Gusty north winds
expected later today.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
An upper level trough remains positioned over mainland Alaska
today, which has shifted slightly westward from yesterday,
weakening the pressure gradient over Southcentral. At the surface,
Middleton Island radar shows snow showers moving in over Cordova
and the north Gulf coast associated with a polar low spinning in
the Gulf, which will continue to produce snow throughout the day.
Kodiak City will also see light snow today as the polar low moves
inland this afternoon before the next big system approaches.

A storm force low will enter the southern Gulf by this afternoon,
which will be the main weather driver through the next few days. A
Blizzard Warning has been issued for Kodiak Island starting this
evening for high winds, heavy snowfall, and reduced visibility
through Wednesday evening. Areas near Kodiak City can expect up to
a foot of new snowfall. Winds switching from a northeast
direction to northwest by Wednesday morning will bring in colder
air, leading to a good set up for Kodiak City to see visibilities
dropping down to a quarter mile or less at times with new snowfall.

As the low over the Gulf moves farther north, a barrier jet will
set up along the north Gulf coast, intensifying the pressure
gradient. This will increase winds for Seward and the Valdez area.
Thompson Pass will also see stronger winds in this pattern, which
has led to a Blizzard Warning being issued for this area as well
starting tonight through Wednesday afternoon. Winds will be the
driving factor, causing whiteout conditions at time, with only a
few inches of new snowfall accumulation. The eastern Kenai
Peninsula could also experience reduced visibilities and blowing
snow as this front lifts northward through Wednesday evening.



&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Thursday Night)...

The weather story this morning remains much the same as the past
several days. Very cold temperatures combined with winds that will
be strengthening throughout the day today will continue to cause
dangerously cold wind chills between 40 below and 50 below over
large areas of the Kuskokwim Delta and Bristol Bay. A reprieve of
sorts is on its way to eastern sections, as a strong North Pacific
low will be making its way into the western Gulf. While this will
only work to strengthen the winds, it will also bring cloud cover
and warmer temperatures to the area, which should at least
somewhat reduce the wind chill threat. Nevertheless, the strong
winds will keep conditions at or around advisory criteria, so the
Wind Chill Advisories for the Kuskokwim Delta and Bristol Bay have
been extended through noon on Thursday.

While the lion`s share of the Gulf low`s moisture will stay on the
east side of the Aleutian Mountains, some of it is expected to
sneak over to the Bristol Bay side, particularly around King
Salmon and perhaps the Iliamna area tonight into the early morning
hours of Wednesday. As some of the low`s energy moves into Cook
Inlet Wednesday evening, it should allow more moisture to make it
over the mountains and into the Lower Kuskokwim Valley Wednesday
night. This could lead to a prolonged period of light snow for the
mountains and the nearby foothills. Since most of the moisture
will be taken up by the mountains, most of the expected
accumulations in the aforementioned areas will be light.
Nevertheless, the threat of snow and definitely the associated
cloud cover will persist through the day Thursday. This will allow
for a warming trend in the temperatures, which were reflected in
tonight`s temperature updates. Despite that, the winds will remain
out of the north the entire time from today through Thursday
night. Thus, despite the warming trend, temperatures will remain
well below normal.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Today
through Thursday Night)...

The big story regarding the Bering Sea and Aleutians forecast will
be the strong low in the Gulf causing northerly winds to increase
across the eastern Bering and Aleutians. This will enhance the
cold air already in place, which upon moving over the relatively
much warmer waters of the eastern Bering, will result in
intensifying ocean-effect snow bands moving into the Alaska
Peninsula and eastern Aleutians. Thus, have increased snowfall
totals across the Alaska Peninsula zone, which in addition to the
strong winds will result in frequently reduced visibilities over
many areas. A Winter Weather Advisory for snow and blowing snow
has been issued for primarily north-facing areas of the Alaska
Peninsula. The snow bands, already impacting the area now, will
strengthen as the winds turn towards the north and eventually
northwest, increasing the length of the fetch over the Bering and
increasing the moisture and snow-making capacity of the ocean-
effect snow. The ocean-effect snow will also impact the eastern
Aleutians, including Dutch Harbor. Conditions will need to be
watched, particularly in Akutan and Nikolski, as low visibilities
in the strong winds are very possible there. For Dutch Harbor, the
north to northwest winds should result in increasing blocking of
the snow by the mountains to the northwest, so no advisories were
issued, but that will need to be watched today for possible
updates.

&&

FROM Mon Afternoon AFD...
.MARINE (Days 3 through 5...Thursday through Saturday)

Gulf of Alaska: Persistent low pressure is expected to remain in
the Gulf through the end of the week. After the leading edge of
the storm force low moves inland Thursday morning, strong
northwesterly to westerly flow is expected on the backside of the
low with gales and storm force gusts over the western Gulf through
Friday. Gap flow winds, especially over Kamishak Bay and Wide Bay
(south of Kodiak Island) will last through the weekend. These gap
winds will likely peak Friday night into Saturday morning.

Bering Sea and Aleutians: Gusty northerly flow is expected over
the eastern Bering Thursday before tapering off early Friday. The
next concern is a gale force low approaching the western
Aleutians Friday. The leading front will move east across the
Aleutians Friday into Saturday, introducing warmer southerly
flow to the southern Bering for the weekend.

&&

.LONG TERM FORECAST (Days 4 through 7...Friday through Monday)

Remnant low pressure over the Gulf of Alaska is expected to move
eastward Friday as a building upper level ridge approaches from
the west. Attention then shifts westward as an incoming gale force
low approaches the western Aleutians Friday into Saturday. While
models remain inconsistent with the track of this low, there is
some potential for a pattern change across southern Alaska for
the beginning of next week as warmer southerly flow pushes
eastward into the Gulf of Alaska.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warnings 131 (Thompson Pass) 171. Wind Chill
 Advisory 161 155. Winter Weather Advisory 181.

MARINE...Storm Warning 119 120 130 131 138. Gale Warning 127 128 132
136 137 139 150 155 165 170-174 176 177 179 180 414.
Heavy Freezing Spray 150 155 165-172 179 185 412 414 121
127 130 138 138-141.


&&

$$

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



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