Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 150127
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
427 PM AKST Sat Jan 14 2017

.ANALYSIS AND UPPER LEVELS...
A closed upper low remains over Southwest Alaska with southerly
flow over the eastern half of the Mainland. A separate low
pressure system that moved onshore the north Gulf coast is pushing
inland. This storm has delivered on the expected widespread
snowfall across much of southcentral Alaska overnight and this
morning, with the lower elevations of the Anchorage and Mat-Su
generally seeing 5-8 inches with locally higher reports reported
in Eagle River as well as up in Hatcher Pass. 1-2 feet of new snow
had fallen as of midday in Valdez, with rain continuing in
Cordova, and closer to 3 inches of new snow reported near
Glennallen. As this storm continues to push strongly into the
interior of the state, strong southerly winds ushering in an
arctic airmass are spreading through the Alaska Range and up Cook
Inlet, causing temperatures to drop throughout the day. Meanwhile,
even as the present storm hasn`t even fully left the area yet, the
next weathermaker is visible on satellite imagery about 500 miles
south of Anchorage. This storm will impact our area by Sunday
afternoon.

&&

.MODEL DISCUSSION...
The models remain in remarkably good agreement given the highly
amplified large-scale pattern and generally fast speed in which
weathermakers are moving into mainland Alaska from the ocean. All
models continue to show the next storm following a similar track
to the current storm, with the notable difference being some
consensus for a bit more easterly track of the low into Prince
William Sound on Sunday night. As with the current storm, very
small deviations in the low track will have huge implications on
the location of the heaviest snow band. At this time the preferred
models are the nam/gfs, which are in good agreement on the low
tracking into the central or eastern Prince William Sound, though
if the low happens to track into Western Prince William Sound the
snow totals could end up significantly higher for the Anchorage
area.

&&

.AVIATION...
PANC...Gusty southerly winds and VFR conditions will continue
through the early evening before the winds begin to diminish. More
benign conditions will prevail for much of the overnight period
and into Sunday morning. Clouds begin to thicken up again during
the day Sunday in advance of the next storm with mvfr cigs and
light snow likely developing sometime early Sunday afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The surface low that moved the front into Southcentral last night
weakens as the frontal boundary moves northeast and diminishes
tonight. A few snow showers will develop along the Chugach and
Talkeetna mountains tonight with only light accumulations
expected. Snow showers diminish after midnight across the
northeast gulf and Copper River Valley as the boundary weakens
as it shifts east.

The next challenging storm system is currently spinning along the
North Pacific 800 miles south of Dutch Harbor. This storm turns
northward tonight as the zonal oriented subtropical jet lifts
north to Southcentral. The occluded surface low tracks north with
a center deepening to 962 mb as it moves toward the gulf. It`s
associated front moves into the southern Gulf early Sunday
morning spreading rain and snow to the northeast Gulf by midday.
Moisture wraps around the backside of this occluded system
bringing snow to eastern Kenai Peninsula and Kodiak Island. There
is some uncertainty in the timing and the track of the surface
low since it is coming up quickly from an area that is sparsely
sampled for data. The front is currently projected to move up to
the coast and Prince William Sound Sunday afternoon, which is much
faster than the surface low associated to it. With southeasterly
flow in the the mid levels, light precipitation is likely to
spread inland along the flow aloft.

The main impacts from this system set into motion Sunday night
into Monday afternoon as the North Pacific storm system`s energy
absorbs into the parent low over western Alaska upon it`s entrance
into the Gulf. The surface low moves at a fast pace toward Prince
William Sound Sunday night spreading precipitation northward
across the Gulf coastal locations and inland through the Copper
River Basin. A strong wave is expected to swing north across
Southcentral bringing another widespread snow event into Monday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Sun and Mon)...
A cold upper level trough will continue to control the quiet
weather pattern across the area. A closed upper level low remains
parked over the Kuskokwim Valley and is anchored by arctic air
diving down its western flank from the north. A few weak impulses
will rotate around the low and help to trigger some snow showers
along the Alaska Peninsula and into Bristol Bay through the period.
Because of the proximity to the low center and its instability,
have opted to leave fog out of the forecast even with some weak
onshore flow. The most challenging part of the forecast will be
clouds and how they impact the temperatures. This airmass could
easily produce temperatures 20 to 30 F below normal. But it looks
like some clouds will linger through the early part of the week
keeping temperatures from bottoming out.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2...Sun and
Mon)...
The main story will be arctic air pushing into the southern Bering
from the Bering Strait area. This will continue to produce cold
air advection snow showers with some gusty winds across the entire
Bering. The best shower potential will be on the Bering side of
the chain. Just south of the chain, a much warmer airmass will
persist. The contrast of these two air masses look to lead to a
polar-low type system setting up between Atka and Adak on Mon.
This could bring some gustier winds and a better chance for snow
for this narrow corridor.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The low pressure system parked in the Prince William Sound region
will be dissipating by Tuesday afternoon. This keeps northerly
flow through the Southwest Alaska region. Therefore, cooler
temperatures from the north filters into the Southcentral, and
Southwest Alaska area. Look for the coldest temperatures over the
Lower Kuskokwim Valley and Bristol Bay interior. The temperatures
will range from minus 20 to minus 30 below range which will
likely create wind chill issues for the Southwest Alaska region by
Thursday. Therefore, look for gusty gap winds to develop through
the Barren Islands, Whittier, and Thompson Passes heading into the
weekend.

Meanwhile, the upper levels have a closed low over the Seward
Peninsula region. This synoptic feature produces shortwaves which
will swing through the Gulf into the Southcentral region through
the weekend. This pattern will be very active in driving storm
tracks across the Aleutian Chain into the Gulf before entering the
Southcentral Region. The models have discrepancies with timing and
placement of the aforementioned synoptic features. Looking at the
jet stream, a strong westerly zonal flow remains south of the
Aleutian Chain with the NAM being the faster model with these
storm systems, while the ECMWF has been slower. This is making the
forecast confidence below average as we head into the weekend.

The majority of the Bering remains in northerly flow with
continued showery regime through Friday, except for a storm force
low developing over the Central Aleutians by Tuesday. This storm
tracks along the chain before crossing the Alaska Peninsula by
Thursday into the Gulf. By Saturday a rapidly intensifying storm
force low tracks just west of Shemya with an associated front
swinging through the Central Aleutians and western Bering. This
brings abundant moisture accompanied by strong southerly winds
with warmer temperatures to the Bering.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Heavy Freezing Spray Warning 121 130 138 139 141 160 165
  180 181 185.
         Gale Warning 119 120 130 131 132 141 150.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...AMD
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...PD



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