Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 200103
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
403 PM AKST Thu Jan 19 2017

.ANALYSIS AND UPPER LEVELS...

Frigid cold temperatures over much of the Mainland remain the main
weather story as areas of Southcentral and Southwest AK continue
to see the coldest temperatures in the last couple of years. The
main perpetrators causing these near record low temperatures are
a closed upper-level low over the northwest mainland and high
pressure at the surface. The upper-level low is transporting
arctic air southward to the southern Mainland while clear skies
and light winds under the surface high pressure are allowing
surface temperatures to plummet.

Further south along the Gulf coast, a trough of low pressure is
weakening this morning. The pressure gradient between the mainland
high and the coastal trough is allowing gusty northerly winds
through favorable channels on the North Gulf Coast and Broad Pass.
These winds have weakened through the morning as the coastal
trough weakens, but still remain gusty at times through the early
afternoon.

In the western part of the forecast area, a surface low pressure
system east of the Pribilof Islands is the main weather driver as
it tracks over the Bering towards the Southwest Coast. The
occluded front associated with the low pushed onshore over the
Southwest Coast early this morning and continues its track inward
over the Southwest Mainland this afternoon. The front is bringing winds
and moderate snowfall to the area, resulting in blizzard
conditions in areas of the Kuskokwim Coast. The Pribilof Islands
are also seeing reduced visibility due to blowing snow as the
occluded front wraps around the back of the low.

&&

.MODEL DISCUSSION...

While previous model runs struggled with the track of the Bering
Low, recent model runs have better converged on a solution. The
models are all now in agreement tracking the low towards Kuskokwim
Bay tonight and moving inland overnight. Models also have a good
handle on the track and timing of the associated front as it
tracks over the Alaska Range tonight and into Southcentral
tomorrow. Some discrepancies do arise in the amount of
precipitation associated with the front Friday through Saturday.
High-Resolution models were used for the forecast to best capture
the local effects and the outflow winds.

&&

.AVIATION...
PANC...IFR/LIFR conditions will lift some this evening at times
before settling in for the night. Conditions should slowly improve
by noon Friday a weather front moves into the area.

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

A the coldest air over the region is shifting to the Copper River
Basin tonight, temperatures are still expected to fall below zero,
except for coastal locations. A front moving across the Alaska and
Aleutian ranges tonight into Fri will bring steadily warming
temperatures through Sat. The front will also spread some snow to
Kodiak late tonight into early Fri, the Kenai Peninsula during the
day on Fri, and the Susitna Valley and western Prince William
Sound Fri afternoon. A weak wave moving along the front will
downslope Anchorage and the Matanuska Valley on Fri, with only a
chance of snow. The upper flow then changes Fri night, allowing
for snow to fall in those areas. On Sat precipitation rapidly
ends as the front stalls and dissipates. As the front approaches
on Fri, the pressure gradient will tighten and some Turnagain Arm
winds will develop.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A storm force low continues tracking towards the Kuskokwim Bay
before moving onshore near Cape Newenham after midnight tonight.
The associated weather front is moving through the region
producing blizzard conditions mainly west of Bethel. The surface
observations at Toksook Bay, and Mekoryuk have been reporting
visibilities one quarter miles or less accompanied by gusty
northerly winds with snow and blowing snow since this morning.
While in the Bristol Bay, and the Lower Kuskokwim Valley, the
greatest amounts of snowfall will occur along the Aleutian/Alaska
Range as the surface low tracks through the Southwest Alaska
region. By early Friday morning the low pressure system will be
located in the Lower Kuskokwim Valley. Therefore, the blizzard
conditions over the Kuskokwim Delta will have diminished except
for some wrap-around moisture making it into the aforementioned
region. Meanwhile, the northerly winds on the backside of this
synoptic feature allows cooler air to filter into the area. This
results in wind chills ranging from minus 25 to 35 below heading
into Friday time-frame. These cooler temperatures combined with
the northerly winds will possibly result in wind chill issues for
the Kuskokwim Delta as we head into Friday night through Saturday
morning time- frame.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The blowing snow conditions with visibilities one half mile or
less at times will continue over the Pribilof Islands through
early Friday morning. They are receiving northerly winds as the
cold air advection strengthens the pressure gradient. The surface
observations at Saint Matthew Island have reported one half mile
or less accompanied by blowing snow with gusty northerly winds
since early Thursday morning through Thursday afternoon. This
coincides with an upper level trough dropping down from the north
through the aforementioned region this evening. This reinforces
the gusty northerly flow combined with snow to keep the blowing
snow advisory extended through early Friday morning. Meanwhile,
look for the gap winds to develop along the Eastern Aleutians, and
the Alaska Peninsula by Friday evening. While the Western
Aleutians has a storm force low tracking near Shemya by Saturday
morning. The associated weather front moves through the Western
Aleutians resulting in gale force southeasterly winds accompanied
by warmer temperatures heading into the weekend.

&&

.LONG TERM FORECAST (Days 3 through 7)...

Beginning the extended period on Saturday evening, there will be
an arctic trough over Southwest Alaska and a storm force North
Pacific low moving into the Western Aleutians. Eventually the
North Pacific low will quickly traverse the chain and move into
the Gulf of Alaska. This will represent a rather large change in
the pattern to warmer and cloudier as the very cold arctic air
mass is displaced north. All the global numerical models depict a
similar pattern with a general trough position located over the
Eastern Bering by early next week. Shortwave troughs rotating
north toward the Gulf coast will bring a pretty continuous feed of
moisture and warmer air northward with the threat for coastal
rain/snow and potentially heavy snow for favored mountain
locations which do well in south to southeast flow environments
(Turnagain Pass, for instance). Inland locations will tend to see
stronger downslope flow conditions but will still be prone to
shots of precipitation as the lows move inland. This very active
pattern looks to continue into the weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 155.
 Blowing Snow Advisory 195.

MARINE...Gale 165 179 180 181 185
Heavy Freezing Spray 121 126-129 139 150-170 172 178 180 185

&&

$$

SYNOPSIS AND MODEL DISCUSSION...RD
SOUTHCENTRAL ALASKA...DS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...JA


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