Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 071358
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
458 AM AKST Wed Dec 7 2016

.ANALYSIS AND UPPER LEVELS...
The western Gulf has a weak 1011 mb low pressure system located
east of Kodiak Island, and is remaining almost stationary. This
is resulting in a showery weather regime extending from the
aforementioned region northward along the northern coastal
communities. While the upper levels are depicting an elongated
deformation zone located over the Tanana Valley extending into the
Bristol Bay interior. This has been kicking off light snow showers
in the Copper River Basin, Mat-su Valleys, and the Bristol Bay
interior last night through this morning. The surface observations
in these regions have been reporting light snow showers with
intermittent MVFR ceiling conditions. Otherwise, an amplified
ridge extends through the Central Aleutians/Bering northward into
the Eastern Siberian region, and through the Brooks Range into the
Beaufort Sea. This massive ridge is bringing cooler air from the
north accompanied by clear skies into the Southwest/Southcentral
region, except for the mostly cloudy condition along the northern
coastal communities. Meanwhile, the northern/eastern Bering is
under the influence of the upper level ridge with northerly flow.
The satellite imagery is showing a large swath of low stratus in
the aforementioned region. While upstream a 962 mb storm force low
is tracking across the Kamchatka Peninsula with the associated
weather front pushing through the Western Aleutians/Bering this
morning. This synoptic feature is bringing warmer temperatures
with gusty gale force southeasterly to the Chain, and the western
Bering.

&&

.MODEL DISCUSSION...
The models remain in good agreement with the Nam/GFS being the
preferred models of choice this morning. The forecast confidence
remains above average through the next several days.

&&

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A weak low centered in the gulf of Alaska will continue to
support widespread but light showers along the northern Gulf of
Alaska coast today. A few snow showers are expected to sneak
across the mountains into Anchorage today, but generally dry
conditions are expected across the Anchorage Bowl and western
Kenai Peninsula. Although the low is fairly weak, the surface high
centered in the north Alaska mainland remains nearly stationary
and potent. The pressure gradient generated by these two features
will sustain offshore flow along the Gulf Coast, especially across
Thompson Pass. The combination of cold air and gusty gap winds
will support cold wind chills especially in the vicinity of
Thompson Pass into at least Thursday. By Thursday afternoon a new
wave will push along the north Gulf Coast, which will result in
more organized and steady snowfall along the northern Gulf Coast
and southern Copper River Basin. However, there is still a lot of
uncertainty in the track of this system.

&&

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

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Aside from some lingering stratus and flurries this morning across
the Bristol Bay region, the pattern for the southwest mainland
will largely be characterized by dry offshore flow through
Thursday on the backside of the trough centered over the western
Gulf. This will yield frigid temperatures beneath mostly clear
skies, although numerous disturbances embedded in the upper level
flow will continue to provide chances for increased cloud cover
over the Bristol Bay region. Persistent gusty winds will lead to
very cold wind chill values across the Kuskokwim Delta, although
these conditions are not expected to meet advisory criteria at
this time.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
An upper level disturbance dropping southward across the Alaska
Peninsula will enhance snow shower activity through this morning
before departing into the Pacific. Scattered showers will persist
through Thursday in cold northerly flow on the western periphery
of the gulf trough, with Small Craft Advisory level winds and
freezing spray continuing to impact the coastal waters of the
southeast Bering. The other main feature of interest in the
Bering is the front bringing rain and storm force winds to the far
Western Aleutians this morning. This front will gradually weaken
as it moves towards Adak and Atka by Thursday, then dissipate
Thursday night as it encounters the ridge responsible for a
relatively prolonged stretch of benign conditions over the central
Bering.

&&

.LONG TERM FORECAST (Days 3 through 7...Fri through Tue)...
The big story in the long term will be continued dry conditions.
On Friday, a weak area of low pressure will drift from the
northern Gulf of AK towards Bristol Bay. This will bring an end
to the last vestiges of any light snow showers along the Gulf
Coast. Into the weekend, a dominant Arctic High will build in from
Chukotka region across mainland AK. This will make for clear and
continued dry conditions. Forecast confidence is high in this
scenario. One difference that will be noticeable will be slightly
warmer temperatures. Climatology puts Anchorage at 10F for a low
and 23F for a high. While things may not be quite this warm, they
should be warmer than last weekend. And while there will still be
an offshore gradient, it will be markedly less than last weekend
as well. Thus, winds through the gaps such as Whittier and
Thompson Pass will be less gusty.

There is some uncertainty in how the ridge breaks down early next
week (12-13 Dec). All models indicate that some energy will make
it over or through the ridge and punch through Prince William
Sound. But there is uncertainty in what happens with said energy
thereafter. At this point, it looks like there will not be
sufficient moisture with that energy to produce any snow, but it
certainly could bring some gusty winds.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory for Thompson Pass...131.
MARINE...Storm Warning...178.
         Gale Warning...127 177.
         Heavy Freezing Spray Warning...140 160 180 181.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...EN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...ML



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