Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 260052
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
452 PM AKDT SAT JUN 25 2016
.ANALYSIS AND UPPER LEVELS...
Scatterometer data shows a weak area of low pressure has developed
south of Kodiak Island overnight. In addition, an upper level low
stacked on top of the surface low has continued to develop with a
weak easterly shortwave propagating across Southwest Alaska. This
wave has brought continued rain showers to much of Southwest Alaska
but is quickly tapering off from northeast to southwest as the
stacked low continues to push further south. Southcentral Alaska
is along the northern periphery of the upper level low which has
allowed a few weak disturbances to traverse the region and bring
some rain showers. High pressure continues to reside along the
northern gulf coast which has kept gusty winds common through east
to west oriented gaps from Anchorage south.
The ridge of high pressure over the Bering Sea has finally begun
to shift eastward as an upper level low over the Kamchatka Peninsula
strengthens. In response, a front and associated surface low
developed across the North Pacific early today and is currently
pushing toward the western Aleutians. The western Aleutians saw a brief
reprieve from almost 60 hours of 200 ft ceilings and visibility
below 3 miles, with a transition bringing clear skies as they
go from a marine stratus environment, to a more convectively
enhanced environment with the advancing North Pacific front.
Models are in good relative agreement with the slow pattern shift
during the weekend. The NAM was the favored model for updates
today as it provided slightly better refinement of the upper level
waves. Better model consistency with stronger shortwaves on Sunday
lead to increasing rain chances across the southern mainland.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The low pressure system in the central Gulf continues to fill,
and remains almost stationary through the rest of the weekend.
The Southcentral region remains under a showery weather regime as
shortwaves push through the region from east to west. The greatest
instability occurs over the Alaska Range, and the Talkeetna
Mountains with Lifted Index`s of -1 degree Celsius as a shortwave
moves through this evening. Therefore, look for a slight chance of
evening thunderstorms in the aforementioned region this evening.
The majority of the precipitation remains along the northern Gulf
coastal communities. Meanwhile the Anchorage Bowl, and the
Western Kenai continue with drier conditions from down-sloping.
By late tonight going into early Sunday morning a second shortwave
tracks through the Copper River Basin westward. This synoptic
feature will be accompanied by steadier showers, and spreads
westward into the Anchorage Bowl heading into Sunday morning.
This will bring cooler air into the region, and dampen the
possibilities of any thunderstorms for Sunday. The gap winds
through the Turnagain Arm remain gusty as the ridge along the
Panhandle builds into the Prince William Sound region through
the rest of the weekend.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2..Sun and
With weak flow and fairly abundant sunshine, the thermal
trough re-established itself today. This allowed for widespread
instability across the Kuskokwim Valley and even stretching down
into the northern reaches of Bristol Bay. A fairly impressive
boundary has set up right along the Kuskokwim Mountains. This
boundary is being reinforced by cool northwest flow over the
Kuskokwim Dela and moist, warm northeast flow from the Alaska
Range. These storms will move from northeast to southwest through
the late evening hours. Sun afternoon and evening will be quite
similar. Convective indices are progged to be nearly identical to
what they are today. The one big difference is that tomorrow there
will be a rather impressive shortwave dropping in from the
northwest. If the timing is right, this could serve as a focus for
thunderstorm activity. Either way, it does look like the best
potential will be just a hair further east tomorrow, from the
Kuskokwim Mountains eastward. Even locations that do not see
thunderstorms will still be susceptible to showers. The lone
exception to that is the Western YK Delta where a cooler and more
stable air mass will keep things dry.
Not much will change by Mon. The thermal trough and associated
showers and thunderstorms will still dominate the pattern. The
only notable difference is that some riding from the Bering Sea
starts to push inland and will shift the best convective potential
further east toward the AK Range.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2...Sun and
Fog, stratus, and light winds will continue to be the story
across much of the Bering with high pressure in charge. A few weak
warm occlusions will skirt through the Western Aleutians bringing
the chance for some light rain Sun. By Mon, a slightly stronger
system pushes into Shemya from the west. This should bring another
chance for rain and should help to dissipate some of the
persistent fog. Over the Eastern Bering and Alaska Peninsula,
the northerly flow will finally give way to some ridging. This
will bring an end to the showers and gustier conditions, but it
will set up a good scenario for low stratus and overnight fog.
.LONG TERM FORECAST (Days 3 through 7)...
Monday afternoon brings a continuation of the current pattern and
conditions into the late week. Mostly cloudy conditions with a few
breaks of sun will prevail. The north gulf coast will see the
brunt of showers in this pattern, while scattered showers will
build on elevated terrain in the afternoon/evening hours around
the rest of Southcentral Alaska. Tuesday will bring nearly the
same conditions with a bit more coverage of rain showers along the
Gulf Coast, but coverage will increase almost everywhere on
Wednesday as the gulf low begins to move overhead. Thursday is
when the gulf system really starts to influence the area, making
widespread rain likely. Toward late week the initial system moves
to the west and weakens while another takes its place in the gulf.
Temperatures will generally be in the 60s inland with 50s along
the coast with light winds, except for diurnally forced gap winds.
SYNOPSIS AND MODEL DISCUSSION...LIW/KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO