Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 181311
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
411 AM AKST Sat Jan 18 2020

.ANALYSIS AND UPPER LEVELS...

A large upper level high centered over the Canadian Arctic is
being displaced eastward by an equally large low tracking
near Sand Point. This is leading to scattered rain and/or snow
showers across much of the Bering/Aleutians. Winds aloft are
advecting an area of moisture associated with a ~980 mb surface
low in the Gulf northward towards Kodiak Island. Easterly winds at
the surface are subsequently causing snow squalls to develop
there, which will generally continue through the day. The most
intense bands are expected to occur this morning. As such, a
Winter Storm Warning is currently in effect. Mostly clear skies
and calm winds encompass much of Southcentral Alaska with the
exception of the usual gusty northeasterly outflow winds in the
Chugach terrain gaps.

&&

.MODEL DISCUSSION...

Models remain in good agreement for the short term. Agreement
begins to deteriorate on Sunday, particularly with the position
of a low tracking into the Gulf and thus confidence is low after
around 24 hours. That said, snow does appear likely along Prince
William Sound Sunday and Monday.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist.

&&

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

The upper level flow will become more southerly through Sunday
night as the upper high over northern Alaska retreats eastward.
This will bring increasing clouds to the southern mainland
beginning Sunday, with precipitation reaching the Gulf coast. Some
snow is possible over the western Kenai and over the eastern
Copper River basin Sunday night.

For Kodiak Island today, expect considerable precipitation as a
strong inverted trough moves across the area from the Gulf. This
precipitation will fall mainly as snow, though some rain could be
mixed in at times with temperatures in the lower to mid 30s. Up
to a foot of snow is possible over the northern portion of the
Island, and considerable winds will create reduced visibilities
in blowing snow as well.

&&

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

The potential for snow showers will increase this morning as
easterly upper level waves push into Southwest Alaska over
Shelikof Strait towards the Alaska Range and Alaska Peninsula.
Through the afternoon, these waves will likely bring snow showers
west of King Salmon to coastal sites, including Dillingham and
Pilot Point as a deformation band sets up through the overnight
hours. There is still some uncertainty as to where the band of
snow showers will set up, but snow accumualtions should be
minimal through the duration. By Sunday, snow showers will begin
to taper off. Increased cloud cover extending across Southwest
Alaska should help to keep temperatures moderate over the next few
days.

&&

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

A front over the central Bering will continue to weaken through
Sunday, which will keep scattered snow showers in the forecast for
much of the Bering, Aleutians and the Pribilofs throughout the
weekend. By Sunday morning, a weak low will enter the northern
Bering, but there is still model uncertainty in where this low
will track and how strong it will be. In any case, expect small
craft advisory winds to be associated with this system, which will
continue to be monitored for future forecast packages.

&&

.MARINE (Days 3 through 5: Sunday through Tuesday)...

The Gulf of Alaska continues to look fairly quiet into next week.
Sunday into Monday a weak low pressure will create small craft
advisory winds along the north Gulf Coast with a barrier jet
there. Beyond that, weather calms. We are confident in this
forecast for the Gulf.

For the Bering Sea, guidance now indicates a compact low now
traversing the Central Bering northwest to southeast. This low is
reflected in the forecast. Gale force winds are forecast on the
backside of this low. High pressure and quieting weather are
expected to move in behind it. There is moderate confidence in
this forecast as the low was not previously depicted by model
guidance. This means it will likely need to be adjusted in coming
days as model guidance gets a better handle on it.

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through Thursday)...

The long term forecast starts with weak low pressure in the Gulf
of Alaska, which will likely be producing snow in the Chugach.
Snowfall amounts and specific locations will be honed in the next
couple of days. This system decays Tuesday and becomes a nominal
factor in the weather. Out in the Bering, a compact low has been
identified by model guidance. This low will cross the Bering Sea
quickly and dissipate as it reaches the Southwest Coast on
Wednesday.

High pressure then builds in behind general low pressure for our
forecast area. A prominent upper level ridge looks to be oriented
southeast to northwest across the Alaska Peninsula into the
Bering. It will reflect as a surface high in the Bering Sea and
likely usher in more cold air for Southcentral AK. Right now the
Mat-Su is on the eastern (downstream and cold side) of the ridge,
so more cold air can be expected, but it will really depend on
where that border sets up and how much cloud cover we get. The
Copper River Basin has a shot to get some really cold air again,
as they will be on the eastern side of the ridge where cold air
will be pulled south from the Arctic. Models are in agreement of
the ridge setting up, but differ on placement slightly. So cold
temperatures will depend on what resolves over the next several
days. With this not occurring until late next week, there is time
to get this figured out.



&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning: 171.
MARINE...Storm Warning: 130.
         Gale Warning: 120 127 131 132 136-139.
         Heavy Freezing Spray Warning: 127 139 160 185.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...AP
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...BB


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