Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 170127
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
427 PM AKST Thu Feb 16 2017

.ANALYSIS AND UPPER LEVELS...
There is an upper level low centered over southwest Alaska. A
front associated with this low stretches south to north across the
central Gulf of Alaska and then bends westward across the Kenai
Peninsula. There are also plenty showers near the core of the low
over southwest Alaska and Bristol Bay. An upper level high is over
the western Bering, with weak flow over the central Bering and
Aleutians. High pressure over western Canada extends into inland
portions of Southcentral Alaska.

&&

.MODEL DISCUSSION...
The numerical models are in fairly good agreement through the
short term portion of the forecast (Saturday afternoon). There are
some differences in the handling of moisture and precipitation
fields, which lowers the forecast confidence a little. Forecast
confidence is thus near normal.

&&

.AVIATION...
PANC...MVFR conditions in light snow are expected from later this
evening through mid-morning Friday. Conditions will improve later
in the morning, although a stray snow shower cannot be ruled out.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Snow will spread northward from the Kenai Peninsula to Anchorage
and the Mat-Su region later this evening as the front over the
gulf continues to push inland. Precipitation will initially be
limited by downslope flow in the evening before mid level winds
become more southerly overnight, with the bulk of the snow
falling from late tonight through the Friday morning rush hour.
Accumulations are expected to remain on the light side, with
heavier snow confined to coastal areas from Seward to Western
Prince William Sound, as well as Turnagain Pass. The Cook Inlet
region looks to transition to more of a showery regime during the
day on Friday in moist southerly flow. A better chance of snow
will then return Friday evening into the overnight hours with the
passage of the main upper level trough as it lifts northward into
Southcentral, with several additional inches possible by Saturday
morning.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Snow showers will continue throughout much of the Southwest
Mainland this evening as the upper level low continues to slowly
weaken as it spins to the north. Most of the shower activity
should occur over Bristol Bay which will remain directly under the
low, but they will also stretch northward into the Kuskokwim
Valley and eastern Delta where a few inches of accumulation are
possible. The Bethel area will generally remain on the very
western edge of the snow, but it wouldn`t be out of the question
to see a light snow shower or two this evening. Further to the
west, persistent area of blowing snow from gusty offshore flow
along the Kuskokwim Delta coast will begin to improve as winds
diminish behind the dissipating low.

For Friday, the upper trough will begin lifting to the north,
bringing generally improving conditions to most areas over the
course of the day. There may be some cloud cover and spotty
showers continuing as an upper level low remains just off to the
north, however any accumulations should be minimal. Generally
clear and cool conditions will then develop for Saturday as most
of the moisture shifts east of the area.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Gusty northerly flow and snow showers will continue for the
remainder of the work week over the Eastern Bering and AK Pen as
widespread cold air advection persists behind the Bristol Bay low.
The showers will generally light with only minor accumulations
expected, through areas of blowing snow are possible near heavier
showers along the Bering coast. Further to the west a weakening
upper low just south of Atka will bring a few inches of snow to
the Central Aleutians through Friday. Conditions will then improve
throughout the area on Saturday as a weak ridge moves overhead,
allowing for showers and winds to diminish. A gale force front
will then approach the Western Aleutians late Saturday, bringing
gusty winds and snow to that area into Sunday.

&&

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

Beginning the long term forecast Saturday evening, there will be a
large closed arctic low over Northwest Alaska with a weakening and
shearing frontal zone moving into the Western Bering Sea. The cold
air associated with the upper trough will be filtering into
Southwest Alaska with temperatures trending well below average.
Some of this cold air will filter into Southcentral by early week
which will push most locations slightly below average. Snow
threats will mainly be over Southcentral where more favorable
dynamics will exist as the aforementioned upper trough digs
southeast. Light snow threats look to linger through Monday
evening before finally ending as the trough moves east and
weakens.

A deep and strong storm force bent-back occlusion is still on
track for the Western Bering Sea Sunday night and Monday. This
will shift the pattern to a much more progressive southwest flow
pattern for Southern Alaska midweek and beyond. With large scale
amplification of the Northeast Pacific ridge, this will also
warm things up by the end of the week which will create some
precipitation type issues for inland locales as thicknesses warm
sufficiently to support some rain mixing in. However, the first
low on Wednesday looks potentially favorable for all snow for
inland locales, but some model runs such as the 18z GFS take this
feature so far south that it completely misses the mainland. For
now will favor a WPC/ECMWF approach which still shows increasing
precipitation chances by late Tuesday into Wednesday.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Heavy freezing spray 179 185 414.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...JA



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