Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 200006
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
406 PM AKDT WED OCT 19 2016
.ANALYSIS AND UPPER LEVELS...
Currently a progressive pattern is in place with an upper level
low south of the Kenai Peninsula pushing eastward south of the
Gulf of Alaska. To the west, a ridge is moving quickly across the
eastern and central Bering and supporting a widespread deck of
stratus clouds. The surface low south of the Alaska Peninsula has
been supporting gusty winds through channeled terrain across the
Alaska Peninsula this morning, but winds are weakening as the low
drifts to the southeast. Water vapor imagery indicates the
development of a triple point low just south of Prince William
Sound that is rapidly moving towards Kodiak Island. This triple
point low is expected to bring gusty winds and showers along the
south and west Gulf of Alaska coasts by this evening.
Models are showing greater uncertainty than average in the short
term today. Even ECMWF ensemble members are showing a wide range
of solutions for the location and intensity of a triple point low
as it moves towards Kodiak Island tonight. The NAM indicates a
more northerly progression of this triple point, and generally
stronger winds along the coast. As a result a blend of the NAM and
Canadian model was used.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A rather impressive storm force occluded front and associated
surface low is moving west across the Northern Gulf of Alaska this
evening. Local buoys and a series of ASCAT passes verified storm
force winds of 50 knots. Rain is moving west into Prince William
Sound as seen on Middleton RADAR, but the echoes are rather weak.
Offshore winds, which are also quite strong, will weaken overnight
as the front moves south and weakens. Leftover moisture and clouds
will move inland around Cook Inlet, and this will set the stage
for a return to wintry weather for inland Southcentral.
An arctic trough digging in from Northwest Alaska will begin
exerting its influence on the Northern Susitna Valley Thursday
afternoon then spread southeast through the night time. Rain and
snow will turn to all snow as far south as the Northern Kenai by
Thursday night with light snow accumulations. Enhanced
accumulations will favor the upslope portions of the Western
Chugach and the Western/Southern Talkeetna Mountains. Cold arctic
air moving in behind the trough may result in slick driving
conditions for the Friday morning commute along the Glenn/Parks
Highways. The front move east Friday with accumulating snow moving
into the Copper Basin and into Thompson Pass. An increasing
pressure gradient will result in increasing northerly winds and
the possibility of some blowing snow through Thompson Pass by
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The Southwest Alaska region will remain under the influence of
northerly offshore flow through the midweek time-frame. This
brings cooler temperatures from the north into the region. As the
high pressure builds into the northern Bering, this begins to
setup for favorable conditions by late Thursday night going into
Friday morning for the Kuskokwim Delta region for the formation of
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The gusty northerly gap winds along the Eastern Aleutians
continues before tapering off by Thursday evening. While high
pressure builds into the northern/central Bering from the Eastern
Siberian region heading into Thursday. This synoptic feature
brings cooler temperatures into the aforementioned region.
Meanwhile, a weak low pressure system over the Western Aleutians
moves eastward along the chain before dissipating by Thursday
afternoon. Then, the next synoptic feature affecting the region
will be a storm force low tracking just south of Shemya with an
associated weather front entering the Western Aleutians by
Thursday evening. This brings a swath of gale force southeasterly
winds accompanied by rain/stratus to the Western Aleutians/Bering
.LONG TERM FORECAST (Days 3 through 7)...
Cold air advection and outflow winds are expected to impact
Southcentral Alaska through much of the weekend until the ridge
axis moves east of the area. After that the main focus in the
extended timeframe will be out west as there is potential for a
strong system to move into the Bering Tuesday. The EC is by far
the strongest with this system, but even it has gotten weaker from
run to run, lowering confidence in a sub 960 MB low. There also
remains significant differences between the different
deterministic and ensemble runs, also lowering confidence.
MARINE...Gale 119 120 130-132 138 139 177 178.
SYNOPSIS AND MODEL DISCUSSION...ELN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD