Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 231354
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
454 AM AKST Tue Jan 23 2018

.ANALYSIS AND UPPER LEVELS...
The pattern of a strong upper level ridge over the Aleutians and
Bering, a large fetch of cold northerly flow over western Alaska
and a deep arctic upper level low centered over northwest Alaska
continues to bring a very cold air mass to Southwest Alaska. A
trough rotating around the upper level low over the southern Gulf
has phased with the arctic trough beginning to dig south has
created a deformation band bringing light snow to southcentral
Alaska and snow showers to the Gulf Coast. To the west, strong
outflow winds continue over the Barren Islands, through the
terrain gaps along Shelikof Strait and Kodiak Island and through
the Alaska Peninsula and across the eastern Aleutians.

&&

.MODEL DISCUSSION...
While there remains some differences in the how models handle the
small scale details of the deformation band running up Cook Inlet
and into southcentral Alaska, synoptically models remain in good
agreement. In the immediate term, the Canadian was preferred as it
seemed to be handling the deformation band and resulting snow
most closely to how things were unfolding on radar. Further out
the NAM was preferred for both domains.

&&

.AVIATION...
PANC...With PANC remaining near the edge of the deformation zone
which is creating the band of snow, expecting to see prevailing
conditions generally MVFR though occasionally lowering to IFR as
slightly heavier areas of snow move through. Lingering snowfall
may persist until late afternoon, but overall ceilings and
visibilities should improve tomorrow afternoon and evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The snow associated with a broad deformation zone extending from
the Western Kenai Peninsula, across the Anchorage Bowl, to the
Mat-Su Valleys will diminish this afternoon. Snow accumulations
generally will be in the 2-4 inch range. Some light snow or
flurries will likely linger into the overnight hours until the
upper trough moves through. Wednesday will bring a return to
somewhat drier conditions and the strengthening of outflow winds
across the eastern Kenai Peninsula and the North Gulf Coast. Gale
to storm force winds/gusts currently over the Western Gulf will
continue through Wednesday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Quiet weather ongoing across Southwest Alaska will be punctuated
by the only real weather hazard...fairly cold temperatures. An
upper level low currently centered just north of the Brooks Range
of northern Alaska will slowly drift southward over the next
couple days. The upper level low center signifies the core of the
coldest air across Alaska. Thus as it moves southward,
temperatures will continue to drop. So with as cold as it has been
across Southwest Alaska the past several days, even colder air is
to come. Low temperatures across the lower Kuskokwim Valley will
easily drop south of 30 below so long as winds remain calm. High
pressure over the area will continue to keep the winds light.
Thus, despite the cooling temperatures, widespread wind chill
concerns are not expected. However, in localized areas of the
southwest interior where the winds do have the potential to
increase through Thursday, wind chill concerns would be a real
possibility.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The weather across the Bering Sea will be a bit more active than
mainland Alaska. A large ridge of high pressure over the central
Bering remains nearly stationary. It is acting as a block on any
significant weather moving into the Bering from the west. A front
attempts to intrude into the Bering on Wednesday, but is only
expected to get as far as Attu and Shemya before shearing out and
dissipating. This is thanks to the giant area of high pressure
over the central Bering. Underneath the high itself, temperatures
are much warmer than those being experienced over the mainland,
but still cold enough that there are some precipitation type
concerns from any showers moving over the area. Stratus remains
dominant over much of the central Bering under the high pressure
dome. The front moving into the western Aleutians will bring
somewhat warmer air to that area on Wednesday, so the predominant
precipitation type at that point will be rain.

For the eastern Bering, which is on the cold side of the high,
continued outflow from Southwest Alaska will keep conditions cold
and showery. In this pattern, upslope snow will continue to be a
constant threat along the Alaska Peninsula, where Cold Bay
experienced snow and blowing snow through much of the day. Gusty
northerly winds will continue through the end of the week,
especially through bays and passes.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Beginning the extended period forecast Wednesday night, the main
story will still be the very cold upper vortex stretching from NW
Alaska to the Gulf of AK. The coldest air mass of this winter will
be moving south into Southern Alaska as 850 hpa temperatures drop
to the -20C to -30 C range. Broad cyclonic flow will extend from
the Bering Sea to a developing low in the Gulf of Alaska as the
cold upper low digs south. Most inland areas will be quite cold
Thursday morning with little to no relief during the day as cold
air advection increases. There is the chance some locations
Thursday actually get colder as the day progresses. Snow along the
eastern periphery of the upper low will spread from the Copper
Basin and North Gulf Coast to the Kenai coast and Kodiak Island as
the low retrogrades west on Friday. The low will eventually dig
south through the weekend which means most coastal locations will
dry out although Kodiak will remain under the threat for
accumulating snow as bands of precip wrap around the upper low
through the weekend.

By Monday, high latitude blocking will have established itself
over Eastern Siberia, keeping all of southern Alaska under the
influence of arctic high pressure and continued below average
temperatures. This pattern will keep the storm track over the far
western Bering Sea.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale Warning 120 127 130 131 132 138 150 155
         Heavy Freezing Spray Warning 121 129 130 131 138 160 180

&&

$$

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


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