Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 011358
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
458 AM AKST Wed Mar 1 2017

.ANALYSIS AND UPPER LEVELS...

The overall longwave pattern remains the same this morning with an
elongated trough stretching from Kamchatka to the North Pacific,
high amplitude ridging over the Western Bering Sea, and deep
troughing over the Alaska mainland. At the base of the trough is
an impressive 510 dm 500 hpa upper low centered just south of the
Kenai Peninsula. There is a 998 hpa surface low in the Northern
Gulf of Alaska with rather impressive cold air advection along the
coast. This is inciting an impressive outflow wind event with
gusty winds across most of southern Alaska. Some local gap winds
are quite strong with local areas of blowing snow, especially out
of the Matanuska Valley where there is transportable snow.

&&

.MODEL DISCUSSION...

The numerical models are in excellent agreement. This holds true
into next week as southern Alaska remains under the influence of
dominant northerly flow with ridging over the Bering. Favored
models were high resolution models to better capture the outflow
winds. Forecast confidence is very high.

&&

.AVIATION... Expect VFR conditions and gusty northerly winds to
persist through Wednesday.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (through Thursday night)
In two words: cold, windy. Overall, little change is expected in
the upper level pattern. The mean position of the upper low
continues over the Gulf Of Alaska through Thursday night. A fairly
strong upper short wave drops south across Kodiak island Thursday
night.

Surface pressure gradients will slacken some today as the Gulf
trough weakens. Gradients will pick up again some tonight with a
significant increase beginning late Thursday morning/early
afternoon and continuing through Thursday night. The strongest
winds look to be across the North Gulf Coast, though strong winds
are also expected through the Matanuska Valley. All the
ingredients (deep cold pool over the Copper River Basin, strong
surface pressure gradients, upper wind support, and deep downward
momentum transport) seem to be lining up for potentially high
winds from Thompson Pass to Valdez Thursday afternoon and Thursday
night. Storm force winds are expected across portions of the
Western Gulf Thursday night. Other than some isolated snow showers
near Kodiak Island, most areas will be dry.


&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (through Saturday)...
Generally clear and clear conditions will continue throughout the
Southwest Mainland through Friday as widespread northerly flow
drags cold and dry air in from the interior. There is a slight
chance that a shortwave diving southward through the area on
Thursday will produce a few very light snow showers, but anything
that does form should be brief and fast moving. Otherwise, cold
air along with gusty northerly winds will bring wind chills to
around 30 below during the overnight hours, especially to the
Kuskokwim Valley where the coldest air will setup. At this point
however it appears that all areas will stay above advisory
criteria through the end of the week as the bulk of the cold air
remains east of the area.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (through Saturday)...
Very little change in the current weather pattern will occur this
week as an omega block over the Central Bering continues to keep a
frontal system confined to the Western Bering. This frontal
system will continue to bring gale force winds along with rain and
snow through Friday. This omega block will then weak as it shifts
to the east on Saturday, allowing rain, snow, and gale force
winds to spread into the Central- Eastern Bering for the weekend.

&&

.LONG TERM FORECAST (Days 3 through 7)...
By the beginning of the extended forecast period Friday much of
the region will have already undergone a transition in the overall
pattern, with a broad upper level trough over much of the
Mainland and Gulf, and strong ridging out west over the Bering Sea
and Aleutians. This general setup will persist through early next
week, which will consist of colder air filtering down from the
arctic and strong outflow winds over parts of the Southern
Mainland. Models remain in good agreement with the overall pattern
into the weekend. As expected though, there is more uncertainty
with regards to the finer details, especially with respect to low
amplitude shortwave troughs diving south toward the Gulf of Alaska
coast Friday through Monday.

All three major global deterministic models, (the ECMWF, Canadian
GDPS, and GFS) along with their respective ensembles, are also
depicting a rather significant bora polar air outbreak across much
of Mainland Alaska. There is potential of seeing 850 hpa
temperatures reaching as low as -20C to -30C across the Southern
Mainland with cold offshore flow along the coast. The March sun
should moderate some of the cold air at the surface, but the
reality of this situation is it will be quite cold and well below
average for the next 7-9 days, dominated by dry offshore flow and
cold interior temperatures.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch 131.
MARINE...Storm 127
         Gale 121 126 130 131 132 136 137 138 139 141 150 155 165
              175 176 177 178 180
         Heavy Freezing Spray 121 126 127 129 130 138 150 160 165
                              180 185.

&&

$$

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



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