Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 201424
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
524 AM AKST Mon Nov 20 2017

.ANALYSIS AND UPPER LEVELS...

The strong vertically stacked low in the southern Gulf reached
its maximum depth early this morning and is now starting to move
south with the associated frontal system stretched across the
northern Gulf following slowly south as well. With the exception
of Kodiak Island which the edge of the frontal system is
currently rotating across, precipitation is ending and skies
clearing across southern Mainland Alaska this morning with gusty
north to northeasterly outflow winds developing.

Over the Alaska Peninsula and the eastern Aleutians, post frontal
cold air advection as well as strong northerly winds aloft have
been bringing strong north to northwesterly winds particularly
through channeled gaps and passes. Ridging is building over the
central Aleutians and central Bering ahead of a frontal system
pushing into the western Aleutians.

&&

.MODEL DISCUSSION...

Models are in good agreement with regards to the deep low in the
Gulf and the trough/frontal system crossing the Bering today and
tonight. The low crossing the Bering on Wednesday however, offers
more challenges. While all the models agree that it will deepen
rapidly, significant differences persist in the track, timing and
strength as it turns southeast and tracks across Southwest Alaska
or along or offshore of the Southwest Alaska coast.

&&

.AVIATION...

PANC...Breezy northerly winds and dry offshore flow will keep
conditions VFR at ANC with high clouds clearing out this morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...

A powerful storm force low over the Gulf of Alaska is showing an
impressive and well defined circulation on satellite as the low
wraps up into a beautiful occlusion. Some very light snow over the
southern Copper Basin continues this morning, but this will end
quickly as weak ridging builds in and offshore winds increase
today. This offshore wind event will tend to favor higher mountain
gaps near the coast with the strongest winds through Thompson
Pass. For inland locales, local winds should be much weaker, and
in some cases, local inversions may keep winds light and high
temperatures quite a bit lower today.

Shortwave ridging will begin to build into Southcentral tonight,
allowing for weakening offshore winds and cold overnight low
temperatures. A shortwave trough in westerly flow will move into
the region Tuesday evening and overnight. However, the upper
trough will be weakening and shearing as it moves east, so snow
threats look minimal given the amount of low level dry air which
will be in place.

&&

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

Breezy conditions will cause blowing snow concerns to persist
through through tonight, before the next system moves into the
region for Tuesday. Before that system arrives, short-wave
ridging aloft will move across the region monday evening into
Tuesday morning, with clearing skies. Winds will generally remain
in the 15 to 35 mph range though, with blowing snow concerns
persisting. Cooler overnight lows will be another artifact of the
departing storm, as colder air continues to funnel in from the
north.

The next in a series of storms will begin to affect the region on
Tuesday, as a low passing by well to the north sends another cold
front across the region. Winds will become southerly ahead of
this feature with widespread light snow developing along the coast
by sunrise, spreading eastward through the day. Accumulations
will be light though with most locations seeing less than 3
inches, even across the interior. Drier conditions and decreasing
clouds return for Tuesday night into Wednesday morning, before yet
another more potent storm arrives for your Wednesday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Strong winds will persist for eastern portions of the AKPEN
and adjacent waters through late morning, with some gusts to 55
mph remaining possible. These winds will decrease through the
afternoon as a shortwave ridge across the west central Aleutians
traverses the region through tomorrow morning.

Just like a scene from a movie you may know, a repeat scenario is
in store for your weather as we head into the Tuesday afternoon
through Wednesday morning time frame. During this time, a 995 mb
low near Shemya Tuesday evening will head northeast while
deepening. Patchy fog is possible along and south of an attendant
warm front, with widespread precipitation developing. This storm
looks to continue to strengthen heading into Wednesday with
increasing winds and precipitation coverage/intensity.

&&

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

On Tuesday, a low well north of the Arctic Circle will bring a
front through the southern portion of the mainland, with a brief
shot of snow for the entire region and some short-lived outflow
winds for the Southcentral area. Tuesday night and Wednesday will
be the literal calm before the storm for most of the state, as a
low pressure system enters the western Bering late Tuesday night
and strengthens rapidly as it crosses the Bering.

Models have been relatively consistent with the track of this
storm varying a little to the south over the past day. Current
forecast is for the low to cross the northern Bering and move
onshore near Nunivak Island late Wednesday night, before moving
southeastward over the Kuskokwim Delta and Bristol Bay before
heading into the Gulf on Thursday night. It is still expected to
be a storm force low and significant winds and waves are currently
in the forecast for the Bering Sea...with some concern for high
winds and seas in the Bristol Bay region on Wednesday. Behind
this storm another northwesterly punch will bring high winds for
the Pribilofs and the AK Pen, not unlike the pattern from this
weekend. As the storm moves into the Gulf, northwesterly outflow
winds will again be the concern for Southcentral on Friday. On
Saturday, the pattern begins again with another low approaching
from the southwest, although this system appears to take a more
northerly track along the Kamchatka Peninsula, hopefully lessening
the wind and wave threat in Alaska for next weekend.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale Warning 119 120 127 130 131 136 137 138 139 150 155
165 172 177 178 180 181 185.
         Storm Warning 132.

&&

$$

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



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