Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 241314
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
514 AM AKDT SUN JUL 24 2016

.ANALYSIS AND UPPER LEVELS...
A shortwave is currently moving through Southcentral and the
Copper River Basin. To the west, a vertically stacked low is
moving across the Kuskokwim Delta. To the south of this low, an
upper level wave is quickly moving southeast across Bristol Bay
and heading out towards the Gulf. Radar shows a swath of rain
across the Anchorage area extending north and east this morning.
Back to the west, showers are streaming in across Bristol Bay and
the AK Pen due to the previously mentioned wave. Additional rain
is moving in across the Kuskokwim Delta from the upper level low
pivoting through the region. Further west, a weak wave is riding a
top of the ridge that sits to the south of the Aleutians which is
bringing scattered showers to portions of the western and central
Aleutians.

&&

.MODEL DISCUSSION...
Models remain in general agreement and have come into better
agreement with the coastal ridge that will develop through the day
today. Models are showing a general trend towards stronger winds,
especially in Prince William Sound and have bumped up wind speeds
in this area. Out west, solutions remain in good agreement as the
upper level low will continue to pivot through the area. Models
continue to show a better defined surface low taking shape across
the AK Pen and Bristol Bay region by early Monday.

&&

.FIRE WEATHER...

The upper level low over the interior of Alaska will continue to
drop south this morning and increase rain chances across much of
the state. Latest radar imagery shows increasing shower coverage
and should become widespread stratiform rain by noon across
Southcentral Alaska. Southwest Alaska will not see as much rain
with the bulk of the moisture and upper level lift shifting east
of the Alaska Range. Southcentral Alaska will see widespread
wetting rains this today with many locations seeing anywhere from
0.2 to 0.4 inches of rainfall. One interesting thing to note is
that although models are in great synoptic agreement, they are
struggling a good bit on the exact timing of rainfall as well as
rainfall amounts. It is quite possible parts of the Copper River
Basin could see rainfall amounts in excess of half of an inch but
only time will tell.

Gusty southeasterly winds will likely develop this afternoon
along Turnagain Arm, Portage Valley and the Copper River Basin in
response to high pressure trying to build along the northern gulf
coast as a weak low moves into the northern gulf. Forecast
soundings show the boundary layer decoupling during the overnight
hours across the Copper River Basin the next few nights which
hints at gusty winds during the day and relatively light winds at
night.

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

A broad upper level low continues to push from the southwest
mainland towards Southcentral. Ahead of this low, diffluent flow
aloft is supporting widespread showers across much of
Southcentral. Shower coverage is expected to increase towards this
afternoon as the low approaches the Anchorage Bowl before being
pushed westward by the upper ridge overnight.

While an unsettled pattern will remain in place across the area
over the next several days, a coastal ridge and associated low
level jet will build along the northern Gulf Coast. This will help
to support local gusts through Turnagain Arm and the Copper River,
and help to support some local downsloping in the Anchorage Bowl and
Kenai Peninsula.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Showers will continue to be abundant as an upper level low slowly
drops south across Southwest Alaska today and tonight.
Additionally, instability along the north side of the low looks
sufficient to trigger isolated thunderstorms over the Kuskokwim
Delta region this afternoon and evening with widely scattered
thunderstorms over the Kuskokwim Valley and northern portions of
the greater Bristol Bay area where lifted indices are between -1
and -2C and CAPE values up to 400 J/kg.

While showers will gradually taper off as the upper low continues
south of the Alaska Peninsula Monday and Tuesday...they still
should increase to scattered to numerous coverage each afternoon
and evening with combination of diurnal heating and moisture
continuing to stream in from east around the north side of the
low.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
Troughs rotating around and trailing behind the low upper dropping
south over Southwest Alaska will sweep across the eastern Bering
bringing west to northwesterly winds and showery conditions. The
west to east running frontal system just south of the Aleutians
will gradually drop south today and tonight. Upper level ridging
will build into the western Bering Monday and Tuesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
There is a northeasterly 80 knot jet streak over the Y-K Delta
streaming into the eastern Bering, and northwesterly 100 knot jet
positioned over the Western Aleutians on Monday. These synoptic
features merge into one jet streak as they dig into the base of
the longwave trough located south of the Central Aleutians. By
Tuesday evening heading into Wednesday this jet streak transitions
to a 100 knot southwesterly jet streak south of the Eastern
Aleutians. By Wednesday this feature will be streaming through
the Gulf into the Southeast Panhandle. Meanwhile, an upper level
closed low will be over the Eastern Aleutians before tracking into
the North Pacific ocean by Tuesday. This feature will move into
the northern Gulf by Thursday before dissipating by Friday. While
a second upper level low will form in the base of the longwave
trough before moving to the eastern Gulf by Friday afternoon. This
will coincide as a deep southwesterly flow develops in the North
Pacific ocean, and extends into the eastern Gulf region by the
midweek time-frame. Therefore, resulting in a wetter pattern as
shortwaves track through the Southwest Alaska region, and swings
around the base of the longwave trough before moving through the
Southcentral region. This synoptic scenario will bring abundant
moisture, and precipitation to the Southwest/Southcentral regions
through Friday. The rest of the Bering and the Aleutians will have
northerly flow with a showery weather regime. While some marine
layer stratus/fog will filter into the region associated with the
high pressure just west of Shemya.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...LIW
SOUTHCENTRAL ALASKA...ELN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...PD


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