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000
FXAK68 PAFC 140040
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
440 PM AKDT Sun Aug 13 2017

.ANALYSIS AND UPPER LEVELS...
There is an upper level low over southern Alaska centered just
south of Prince William Sound, moving rapidly eastward. Some
moisture from this low is pushing into the eastern portion of the
Copper River basin, and there is also some moisture on the back
side of the low over the middle to lower Kuskokwim River basin.
There is an upper level trough extending westward from this low
over the northern Bering Sea. Fairly zonal flow exists to south of
these features, with some ridging over the southern Bering and
Aleutians. There is an upper level low south of the Central
Aleutians in this zonal flow moving rapidly eastward.

&&

.MODEL DISCUSSION...
The numerical models are in good agreement through the short term
portion of the forecast (Wednesday afternoon). One notable
exception is in how they deal with a low that moves across the
Gulf Monday night and Tuesday. There is considerable spread
amongst the models, though the GFS and ECMWF are fairly close to
each other. There also begin to be some timing differences
starting later Tuesday with features moving southward along the
west coast of the state riding the polar jet. Over-all, forecast
confidence is near normal except below normal over the Gulf marine
waters and Kodiak Island.

&&

.AVIATION...
PANC...VFR conditions and light winds will likely persist. There
is a chance of some fog and/or stratus in the morning with light
winds, some clearing, and high low level moisture levels.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Shower activity will continue to trend downward overnight as the
upper low moves off to the east. This will leave Southcentral in a
benign cloudy and showery pattern through Tuesday as weak cyclonic
flow persists between multiple upper lows embedded within the
longwave trough over the region. Showers will mainly be confined
to the mountains and areas along the Gulf Coast, with any
precipitation generally limited to a few sprinkles from the Cook
Inlet region into the Mat-Su. Abundant low level moisture from the
recent rains and partial clearing overnight will lead to possible
fog development early Monday morning from Cook Inlet across the
North Gulf Coast. Another Arctic trough approaching the region on
Wednesday looks to be bring widespread stratiform rains back to
the region for the second half of the work week.

&&

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

A low over Southcentral Alaska this evening continues to drive the
weather pattern over the area this afternoon. The wraparound
region west of the low is over the Lower Kuskokwim Valley, and
continues to cause light rain for locations in that area,
including Sleetmute and Sparrevohn. Across the Kuskokwim Delta, a
weak disturbance taking advantage of some limited sunshine has
caused an area of vertically developed cumulus and showers to
develop, with some potential for one or two of them to develop
into brief thunderstorms. The showers present across Bristol Bay
are expected to remain as such, with gusty winds blowing in from
off the Bay and holding temperatures down.

Other than a few isolated showers Monday and Tuesday across the
area, much of the region will remain dry under mostly cloudy skies
until the next big rain maker moves in Tuesday night into
Wednesday.

&&

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

A fairly steady state weather pattern is setting up across the
Bering for the next couple days. The one change is the low south
of the central Aleutians is expected to continue moving eastward,
such that it will be out of the area by Tuesday. Other than that,
general low pressure across mainland Alaska and building high
pressure over the western Aleutians will continue to support
broad north to northwesterly flow over nearly all of the Bering
for much of the week. Periodic disturbances moving southbound out
of the Arctic around a broad cold upper level trough will act to
intensify the winds with time going into midweek.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The models seem to being doing better as they depict an upper
level closed low over the Chukchi Sea, and over the eastern
Bering by Tuesday time-frame. These features are on track to move
eastward as the closed low over the Chukchi Sea drops southward
into the northern Bering. While the other low over the eastern
Bering dissipates into a trough, and extends through the Southwest
Alaska region into the North Pacific Ocean by Wednesday. This
trough swings eastward before tracking through the Southeast
Panhandle by Friday. Meanwhile, the closed upper level low over
the northern Bering continues to track southward before moving
over the Alaska/Aleutian Ranges by Friday. This synoptic feature
tracks into the northern Gulf by Saturday morning, and moves along
the Southeast Panhandle going into Sunday. As these upper level
closed lows track through the Southwest/Southcentral area, they
will kick-off shortwaves through each region producing a showery
weather regime. Look for timing/intensity issues with these
troughs as they move through the different regions. Therefore,
the forecast confidence is average at best with continued cooler,
and wet conditions as we head into next weekend.

&&

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

&&

$$

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...CB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JOE
LONG TERM...PD