Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 241300
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 AM AKDT SAT SEP 24 2016

.ANALYSIS AND UPPER LEVELS...
A weakening upper level trough centered over the western mainland
continues to bring widespread clouds and showers to much of the
Gulf and southern mainland. This upper low continues to bring a
pool of cold air aloft, which has created some thunderstorms along
the Gulf Coast and Cook Inlet mainly during the afternoon and
evening hours. These are beginning to diminish however as
temperatures aloft are warming in advance of a ridge of high
pressure approaching from the Bering. This ridge has brought
clearing skies and diminishing winds to much of the
Bering/Aleutians, with the exception of the Eastern Bering/AKpen
where gusty northwesterly winds are occurring. Just south of the
Gulf, a 160-kt jet is beginning to move into the extreme southern
Panhandle. This jet will begin to move northward into the Gulf
today and weaken as the upper level trough begins to lift to the
north.

&&

.MODEL DISCUSSION...
The models remain in very good synoptic agreement through this
weekend, and are coming more into line with each other with the
front that will develop over the Bering on Sunday. In the early
term, there are some differences in the strength of a barrier jet
over the north Gulf Coast this morning. The stronger GFS solution has
initialized the best with this feature based on overnight buoy
observations, so that was favored through the short term.
Otherwise the models are in very good agreement through the short
term, so forecast confidence is good.

&&

.AVIATION...
PANC...VFR cigs with VCSH through this afternoon, then an upper
disturbance will produce more numerous shower activity this
evening into the early morning hours Sunday, when ceilings may
occasionally drop to MVFR between 03z and around 12z. South to
southeast winds will continue occasionally gusty, and gradually trend
downward through the day.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A slowly propagating trough sits over western Alaska, leaving
Southcentral in generally unstable southwesterly flow owing to a
pool of -30C to 31C air aloft and climatologically maxed sea
surface temperatures. Showers will be the general rule across much
of the area through Sunday and should taper off from the west
Sunday night as a trough moves east of Cook inlet. The majority of
thunderstorms today and Sunday will likely continue over the
warmer waters of the Gulf and upslope locations along Gulf coast. To
a lesser extent thunderstorms are possible across the Susitna
Valley and Talkeetna mountains this afternoon and tonight as a
cold pool of air aloft moves across the area.

A weak barrier jet develops today along the north Gulf as a weak
low retrogrades west bringing small craft conditions which will
clip Prince William Sound. Winds will diminish tonight. Westerly
to northerly outflow conditions will develop over the Eastern
Kenai Late Sunday night after trough passage.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
An upper level longwave trough continues to track eastward through
the Southwest Alaska region before exiting into the Gulf by late
Sunday afternoon. This synoptic feature will produce a showery
weather regime before tapering-off with drier conditions as a weak
ridge of high pressure moves into the region from the eastern
Bering Sea. Therefore, areas of patchy fog to develop after
midnight tonight as the ridge of high pressure builds into the
region.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The central/eastern Bering is dominated by northwesterly flow
which is filtering into the Eastern Aleutians, and resulting in
some gusty gap winds. These gap winds will diminish in the
Unalaska region this morning, but remain gusty along the Eastern
Aleutians through Sunday. Meanwhile, a 994-mb low drops down off
the Kamchatka Peninsula into the northern Bering by Sunday
morning. This produces southwesterly flow through the Western
Aleutians/Bering through Sunday. Look for the Bering Sea, and the
ALeutians to be influenced with a showery weather regime with
warmer temperatures accompanied by patchy fog through the weekend.

&&

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

From previous discussion...

It looks like much of the Alaska mainland will be heading into a
drier period over the weekend and into the middle of next week as
the upper level trough currently anchored across the state finally
displaces eastward. Weak ridging will develop over Southwest
Alaska Sunday afternoon but be short lived as an upper level low
drops south across the eastern Bering Sea and flattens out the
ridge. This will likely keep coastal locations of the Kuskokwim
Delta and Bristol Bay area under some light steady rain but inland
locations still should remain fairly dry. Stronger ridging will
build across the mainland Tuesday evening and overspread much of
the state by late Wednesday but a progressive shortwave trough
should push through Southwest and Southcentral Alaska on Thursday
and bring one quick shot of rain before another period of dry
weather settles in.

The Bering Sea will be quite active looking at the grand scheme of
things with a series of longwave troughs passing through the
region. Associated with these troughs will be a series of fronts
that will push through the Bering Sea. The first will be on
Tuesday and the second on Friday. The Friday front looks quite
impressive albeit seven days out. A merger of the arctic jet
stream and a branch of the subtropical jet over eastern Russia
will allow for a strong low to develop over Kamchatka with the
associated front moving into the Bering Sea on Friday. Currently
25 to 30 kt winds are advertised in the forecast due to large
temporal discrepancies amongst guidance. However, winds
approaching 40 to 45 kt will be possible depending on the strength
of the upper level support and timing of a jet streak.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Advisory 145.
MARINE...None.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...DEK
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...MC


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