Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 131642 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
741 AM AKST Mon Jan 13 2020

.ANALYSIS AND UPPER LEVELS...

An upper level trough remains in place over the northern Bering
while a ridge axis is in place over the Alaska-Yukon border.
A broad upper level ridge is in place south of the Aleutian Chain,
bringing a large area of zonal flow to much of the Bering. A weak
upper level shortwave over the central Gulf continues to move
toward the southeastern Gulf. The associated surface low is also
quickly departing the area, leaving gusty northwesterly flow in
its wake.

&&

.MODEL DISCUSSION...

Model solutions remain in good agreement for the short term and are
consistent with the eastward progression and amplification of an
upper level ridge over the Bering midweek. There is also good
consistency regarding conditions upstream of the ridge as a front
associated with a complex Kamchatka low arrives over the western
Bering midweek. Models have been fairly consistent in the timing
and strength of this next system, leading to above average
forecast confidence.

&&

.AVIATION...

PANC...MVFR to IFR conditions in snow are expected through
early Monday morning. MVFR ceilings may be slow to lift to VFR.
Fog in place over Cook Inlet may intermittently lower visibility
at the terminal through the early afternoon. Light winds are
expected.

&&

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

An upper trough and weak surface front move east across
Southcentral today. Light snow across the Cook Inlet to MAT-SU
corridor will taper off through this morning as light snow or
flurries move east into the Copper River Basin. Clearing will
likely be slow with stratus and some fog lingering into the
afternoon hours from Cook Inlet to the MAT-SU Valleys, including
the Anchorage Bowl. Clearing of higher clouds will continue
through tonight, however, subsidence with a building upper ridge,
will trap low level moisture and give rise to areas of fog and
stratus over inland areas of Southcentral. Temperatures, although
warmer than in former days, will start to cool down again over
the next couple of days with 850 mb cold advection. Outflow winds
will strengthen across the Kenai Peninsula and north Gulf through
Tuesday night. Cold ambient temps combined with gusty winds will
continue low wind chills through Thompson Pass through Tuesday
night. Depending on the degree of cooling, Broad Pass could see
wind chills approaching 40 below late Tuesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Monday
through Wednesday)...

Southwesterly winds are in place behind a frontal system that
pushed through the region yesterday. Winds will switch to a more
northwesterly direction tonight, as high pressure builds into the
eastern Bering Sea and slowly tracks east through Wednesday. This
high will be the main weather story the next couple of days as it
maintains influence over the area. It will keep weather dry along
with cool temperatures. It looks to be a quiet couple of days for
Southwest Alaska.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Monday through Wednesday)...

Zonal flow is present over the Bering while a weak wave is moving
through the central Aleutians. This will all change later today
as high pressure builds into the eastern Bering. Once the high
builds in, it will maintain its influence the next couple of days
as it drifts east. This means quiet weather for the eastern Bering
and eastern Aleutians. Out west, a strong front ahead of a low
pressure system will enter tonight. The strongest part of the
front will arrive tomorrow morning, with storm force winds
forecast for the western Bering/Aleutians. This front will slowly
work its way east to be over the central Aleutians Wednesday, as
the high pressure system to its east slows it considerably. So,
all is quiet in the eastern Bering with active weather out west.

&&

.MARINE (Days 3 through 5)...
On Thursday, a storm force low over the northern Bering exits
north overnight while another North Pacific low develops south of
the central Aleutians. There is high uncertainty on the track and
strength of this low on Friday. A second system we are monitoring
is expected to develop across the eastern Gulf Friday night. Once
again, there is high uncertainty on the development of this storm
which could have impacts across the Gulf through the weekend.

&&

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

The forecast beginning on Tuesday night across Southcentral will
see a shift toward colder temperatures as a cold front across the
northwest tracks to the Gulf. This front and northwesterly flow
setting up aloft, will increase offshore flow and also along north
to south oriented gaps Tuesday night through Friday. There will
be several wind peaks Tuesday through Friday. The largest focus
for winds in the extended forecast included Broad Pass, Matanuska
Valley, Seward, Whittier, Thompson Pass, Valdez, and the Copper
River Delta.

Active precipitation is expected to mainly impact the Bering and
the Gulf Tuesday through the weekend. Tuesday night a front along
the Bering is reinforced with another developing low along the
base of the trough. This strengthens the front to storm force with
the upper level wave lifting the system to northern waters
Thursday night.

There is high uncertainty in the forecast Thursday through the
weekend as models diverge greatly on the development of two new
storms...one along the western Aleutians and the other over the
eastern Gulf. The extended forecast during this time was updated
with ensemble blends of the GFS and ECMWF which leads to a very
weak pattern advertising higher chances for precipitation across
the Bering and Gulf with a colder and drier pattern over the
southern mainland.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory 131, Flood Advisory 121.
MARINE...Storms: 175, 177, 178, 411, 412, 413.
Gales: 127, 130, 131, 132, 150, 173, 174, 176, 179, 185.
Heavy Freezing Spray: 119, 121, 127, 129.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...KO
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BJB
MARINE/LONG TERM...KH



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