Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 081423
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
523 AM AKST Thu Dec 8 2016

.ANALYSIS AND UPPER LEVELS...
The weather over much of the mainland is dominated by strong high
pressure eastern Bering into the interior. To the south, a broad
and complex low stretching from the Gulf into the North Pacific is
bringing cloud cover and snow showers to much of the Gulf Coast
along with gusty offshore flow from a persistent pressure
gradient. This low will be the focus for much of the weather
throughout the Gulf and southern Mainland through the work week as
a series of waves continue to rotate around its periphery. The
first of which is beginning to reinvigorate showers the northern
Gulf as the approaches from the east. Over the eastern half of
the Bering gusty northerly flow and cold air advection showers are
beginning to diminish as the ridge of high pressure over the area
weakens. Further west over the Central Bering, a weakening front is
falling apart as it runs into mid level ridging, and will
dissipate over the eastern Aleutians by this evening.

&&

.MODEL DISCUSSION...
The models remain in very good synoptic agreement into this
weekend, with the primary concern being timing of the waves
rotating in the Gulf today and its resulting snowfall to the Gulf
Coast. The NAM has been very consistently the slowest solution
with the first wave beginning this morning, while the GEM
regional has been equally consistent in a much faster solution,
The timing of which were generally ignored for the morning
forecast update. There is also some uncertainty in how much snow
will move across the Chugach into Southcentral from this system,
especially from the higher resolution NAM and GEM regional which
are by far the most aggressive. The GFS was generally the
preferred solution both for its middle ground solution with
timing, but also for bringing a brief round of light snow into
Southcentral Thursday night. Confidence in both timing and precip
amounts are below average however given the spread in the model
solutions.

&&

.AVIATION...
PANC...VFR conditions with north winds around 10 kt will continue
through this afternoon. Starting this evening light snow moving
into the area will likely bring ceilings down to around 4000ft.
Confidence on when exactly the snow will begin is low as guidance
ranges from as early as 00z to as late as 08z, so the current
a middle-ground approach. Once is begins, there is good confidence
that will be a relatively quick round of snow producing less than
an inch accumulation that will dissipate by early Friday morning.

&&

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

Radar imagery this morning indicates sporadic showers that
stretch across the Eastern Kenai Peninsula to Kodiak Island.
Meanwhile, a much broader and more intense swath of precipitation
is slowly pushing northward from the Gulf of Alaska towards Prince
William Sound. This band of precipitation is associated with an
approaching inverted trough that is sweeping from east to west
across the Gulf. This system is associated with impressive low to
mid level isentropic lift. As a result, snow is still expected to
fall in places where downsloping is expected to occur, such as in
Valdez. Meanwhile, at higher elevations in Thompson Pass, the
combination of light to moderate persistent snow, and gusty gap
winds is likely to result in blizzard conditions through much of
today.

Models remain unusually uncertain for today`s forecast. They
disagree on how far north precipitation will spread today, and
how much will reach Anchorage. With a potent ridge in place, it is
likely that most of the precipitation across the Anchorage Bowl,
and Eastern Kenai Peninsula will remain very light tonight.
However, there is still uncertainty and the trough could push
farther north than expected. There is more certainty in several
inches of snow falling in Kodiak Island, and the Eastern Kenai
Peninsula through tomorrow morning.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The Southwest Alaska region continues with offshore flow through
Friday. This results in cooler frigid air filtering in from the
north accompanied by mostly clear skies. The wind chill values
through the Kuskokwim Delta, and the Lower Kuskokwim Valley will
range from minus 20 to 30 below zero as we start heading into the
weekend. While the Alaska range, and the Alaska Peninsula will
have some scattered snow showers spilling over from the western
Gulf region into the Bristol Bay interior through this afternoon.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The western Bering through the Central Aleutians is being
influenced by a weather front this morning. This synoptic feature
continues to weaken as it tracks northward before exiting the
region by late Thursday evening. This gives way to weak high
pressure moving into the aforementioned region. By Friday morning
a storm force North Pacific low tracks south of Shemya. While, an
associated weather front moves through the Western Aleutians with
gale force southeasterly winds. This brings warmer temperatures
with abundant moisture and stratus. Meanwhile, the northern/eastern
Bering has north to northeasterly gusty wind flow accompanied by
cooler air. This will continue to produce freezing spray issues
in the Bering Strait southward into the eastern Bering through
Friday.

&&

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

High latitude blocking will be the dominant mode across the Alaska
region beginning Friday evening as a stout upper high builds
across northern Alaska. Even though temperatures aloft will
actually be warming in response to this feature, temperatures at
the surface will be dominated by increasing inversions.
Temperatures will once again fall below climatological norms by
the weekend as skies clear and outflow winds continue. While the
numerical models differ in the exact details Tuesday through
Friday of next week, the ensemble and multi-model approach all
depicts similar sensible weather outcomes as ridging rebuilds
across the eastern Bering Sea and western Alaska. Offshore flow
will remain dominant across Southcentral with no precipitation
events expected in the foreseeable future for inland locales. In
other words, continued cold and dry with the main storm track over
Siberia and the far western Bering Sea.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning Thompson Pass.
MARINE...Gales 127 128 178. Heavy Freezing Spray 160, 180, 181,
185

&&

$$

SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHCENTRAL ALASKA...ELN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...JA/TP



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