Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 010034
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
434 PM AKDT WED AUG 31 2016
.ANALYSIS AND UPPER LEVELS...
Another beautiful day is unfolding across the southern mainland as
upper-level high pressure centered near the Bering straight
continues to promote dry offshore flow and abundant sunshine.
Gusty winds through the typical gaps in the mountains are on the
decline as the surface high pressure over northeast Alaska
weakens in tandem with the aforementioned upper high center. There
is a shortwave trough diving southeastward through the eastern
Brooks Range currently, and this feature will be crossing through
the Copper River Basin tomorrow bringing some cloudiness and maybe
a few showers. Meanwhile, a large vertically-stacked low over the
central and eastern Aleutians isn`t moving much as the longwave
trough remains in place. A weak associated front is draped from
the southern Bering across the eastern Aleutians and into the
North Pacific...but is struggling to produce winds in excess of 30
mph or so.
With a fairly slow-changing weather pattern over the next several
days the models are all in excellent synoptic agreement. All
models show a weak triple-point low forming south of the AKPEN and
along the weather front tomorrow (Thursday). This will slow the
already-slow northward progress of the front even more. The NAM
is a bit faster than the other models with this low, and as a
result is a bit weaker with the induced ridge of high pressure in
the Gulf ahead of the low. The afternoon forecast will be trended
generally toward the GFS for this reason, with the main impact
being to keep the westerly winds through the Barren Islands and
central Gulf a bit higher than the NAM would suggest.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
High pressure will remain over south-central Alaska through
Friday afternoon. The flow aloft will gradually shift from
northeast to northwest as the high center retreats westward into
northeast Russia. Warm daytime temperatures will continue, with
some daily records likely to fall again through Friday. Overnight
temperatures will plunge to near or below freezing in well-
sheltered low spots and protected valleys away from the larger
bodies of water. Such examples of locations likely to experience
near- or below-freezing temperatures include East Anchorage, the
Eagle River Valley, and Copper River Basin. With the lack of
widespread sub-freezing temperatures, we have opted to cover this
with a Special Weather Statement.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
An upper level ridge remains positioned over the Southwest Alaska
region before becoming elongated through Thursday. The winds will
remain weak with northeasterly flow through the Kuskokwim Delta,
and the Lower Kuskokwim Valley, while the Bristol Bay region is
influenced by weak southeasterly flow. Therefore, look for patchy
fog to develop during the overnight hours for the aforementioned
region before diminishing by late Thursday morning time-frame.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The weak North Pacific low located near Shemya this evening
continues to gradually move southward of the Western Aleutians.
By Friday this feature will be located just south of the Rat
Islands. Therefore, the Bering Sea will have a showery weather
regime accompanied easterly winds, except for stratiform rain
along the Central/Eastern Aleutians heading into the weekend.
.LONG TERM FORECAST (Days 3 through 7)...
Medium to extended range guidance continues to show good overall
agreement on a return to a more seasonally typical cool and
showery pattern for the southern Alaskan mainland by late this
week as the broad North Pacific/Aleutian low makes gradual
eastward progress. The chance for precipitation will return to the
region Friday evening as a front associated with the low moves
inland over the southwest mainland before approaching the gulf
coast late Saturday and moving inland over Southcentral AK on
Sunday. The arrival of the front will be accompanied by broad
onshore flow ahead of the approaching low, which will facilitate
the transition to a more cloudy and showery regime through the
middle of next week as the low opens up into a trough encompassing
much of the mainland. Over the Bering region, the departing low
will be replaced by weak flow aloft and at the surface, likely
yielding widespread stratus and fog.
SYNOPSIS AND MODEL DISCUSSION...AD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD