Area Forecast Discussion
Issued by NWS Anchorage, AK

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155
FXAK68 PAFC 251256
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 AM AKDT Tue Jul 25 2017

.ANALYSIS AND UPPER LEVELS...
Water Vapor Satellite imagery shows a shortwave trough moving east
across the Kuskokwim Delta and eastern Bristol Bay early this
morning. The Bethel radar additionally shows a defined mesoscale
feature spinning over the Kilbuck Mountains with slow eastward
progression. Rain is developing along this low with the heaviest
accumulations along the eastward facing slopes. Light rain showers
are also continuing to develop along the northern Cook Inlet to
the Talkeetna Mountains as a weak shortwave propagates toward the
gulf and Copper River Basin. To the West, a ridge resides centered
just south of the central Aleutians. Abundant moisture is
streaming along the flow and across the Bering around the ridge
perimeter.

&&

.MODEL DISCUSSION...
Models are in relatively good agreement through the short term
forecast through early Thursday, therefore only minor edits were
made in the morning package. NAM was favored for wind details with
a blended model approach for the timing and coverage of rain.

&&

.AVIATION...
PANC...Weak low pressure over the Cook Inlet brings light rain
and MVFR ceilings through the morning with improving conditions
expected in the afternoon. Hi- res models are still not in
agreement on the next wave early Wednesday which will likely
bring ceilings back down to MVFR along with additional rain
showers. Look for future updates for the next front to push
through during the morning hours on Wednesday.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
An upper level front will remain over south central Alaska into
Wednesday while slowly pivoting counter-clockwise. This will
keep light rain and showers over the area. An upper level low
will push southward through southwest Alaska late tonight into
Wednesday. This will create fairly good dynamics over the area
from the Kenai peninsula northward through the Susitna valley for
an increase in rain. This low will then dive south into the
western Gulf Wednesday night, with showers diminishing over much
of the area. The exception to this is the Copper River basin,
where chances of precipitation will increase in northeasterly
flow.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The Southwest Alaska region has a meso-low moving west to east
through the lower Kuskokwim Delta with the remnants of a weather
front as it gradually tracks eastward before dissipating by this
morning. This synoptic feature keeps a showery regime over the
AOR. While an upper level low over the northern Bering drops
southward into the Y-K Delta region by Tuesday afternoon. This
closed low tracks into the Bristol Bay area by Wednesday afternoon
before exiting into the North Pacific Ocean by Thursday morning.
This produces more precipitation across the Southwest Alaska
region through Wednesday afternoon timeframe. Look for the marine
layer stratus accompanied by fog to develop along the Southwest
Alaska coastline this morning. By Wednesday morning the fog will
redevelop only along the Kuskokwim Delta coastline.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The Bering Sea/Aleutian remains dominated by an upper level closed
low located just south of Shemya with an associated ridge
extending into the western Bering. This ridge becomes amplified,
and extends through the Western Aleutians into the northern
Bering by Wednesday afternoon. This feature continues to bring
widespread marine layer stratus/fog to the AOR through the
midweek. By Tuesday night a wave of precipitation rounds the top
of the aforementioned ridge, and tracks into the central/eastern
Bering Sea by Wednesday morning. There is an upper level shortwave
associated with this wave of precipitation, and will strengthen
the wind gradient along the Eastern Aleutians Tuesday night
through Wednesday morning. This synoptic feature produces gusty
northwesterly gap winds along the Eastern Aleutians during the
aforementioned time-frame.

&&

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

The forecast for Thursday and into the weekend continues to be a
challenging one. The upper levels across Southcentral will be
dominated by a low that will practically anchor itself in the
southern Gulf of Alaska. At the surface, a weak ridge of high
pressure will try to nose into Prince William Sound this weekend,
increasing the chances for Turnagain winds. The overall pattern is
a bit of a sloppy one. With an influx of moisture and persistent
onshore flow, coastal areas should see showers leading into the
weekend. The Anchorage area may be spared with the usual
rain shadow/downsloping - but it is still too early to hone in on
those specifics. Long range guidance is beginning to hint at
another ridge of high pressure expanding across Canada and into AK
beyond the forecast period (e.g. next work week) meaning dry and
warm weather could be on the rebound. Out west across the Bering
and Western Alaska, continued summertime stratus dominating the
forecast. The biggest weather player of note is a well agreed upon
system that will dive towards NW Alaska from Siberia Thursday,
bringing a large area of rain with minimal thunder chances. All
guidance members are in excellent agreement with this feature and
forecast confidence into the weekend is high.

&&


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

&&

$$

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



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