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FXAK68 PAFC 240058
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
458 PM AKDT Thu Mar 23 2017

.ANALYSIS AND UPPER LEVELS...
A short-wave which dropped into the long-wave trough sitting over
Southcentral Alaska and the Gulf of Alaska last night is now
helping to kick the entire trough eastward. There are some showers
out ahead of this trough, focused along a surface trough over the
central Gulf. A few clouds and isolated showers extend northward
through the Cordova area and into the Copper River Basin.
Otherwise, clear and cool conditions continue to dominate the
southern Alaska mainland and eastern Bering Sea regions.

Meanwhile, a large deep vertically stacked low (with estimated
central pressure of 965 mb) around 700 miles south of the Aleutian
chain is tracking slowly northward. An east-west oriented occluded
front is spreading out from the low center, leading to increasing
easterlies along the Aleutians.

&&

.MODEL DISCUSSION...
Model remain in excellent agreement through Friday night and
forecast confidence remains high.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

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

Some moisture from the Gulf make bring a few snow showers inland
tonight across eastern Prince William Sound and into the Copper
River Basin. Otherwise sunny days and clear nights will continue
across the rest of the region through Sat. Gusty winds through
channeled terrain will also continue as northerly surface winds
persist.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The upper level ridge over the eastern Bering will persist through
the weekend with a cold upper level trough stretching from
northern Alaska into Southcentral Alaska. This flow pattern will
put Southwest Alaska under northwesterly flow aloft with the
surface winds out of the north to northeast bringing continued
cool, dry and generally sunny weather.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A gale force frontal system approaching from the south will reach
the western and central Aleutians overnight tonight, bringing
gusty winds and rain to the area. The front will lift into the
southern Bering Friday and Friday night. Several additional
frontal waves spinning around the parent low south of the
Aleutians will rotate north across the Aleutians over the weekend.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The ridging over the Bering Sea continues through Saturday before
an upstream North Pacific low pressure system pushes the ridge
into the Gulf of Alaska by Monday. Meanwhile, an upper level
closed low will be positioned over the Anchorage Bowl with an
associated trough extending into the Gulf from Saturday through
Tuesday, before merging with several weak North Pacific Lows.
While the next major storm force low tracks towards the Eastern
Aleutians by Thursday morning, with an associated weather front
entering the Gulf. This brings a pattern change with the offshore
flow over the Southcentral region diminishing, and shifting to
onshore southerly flow. There is uncertainty with timing of how
long the arctic trough stalls over the Southcentral region. The
GFS model is showing a faster solution, and the ECMWF was slower
with this synoptic feature. Meanwhile, by Thursday the jet stream
transitions to a southwesterly flow just south of the Eastern
Aleutians extending eastward into the lower southeastern Gulf.
This enhances storm tracks from the North Pacific area into the
Eastern Aleutians/Gulf region. The forecast confidence is low as
we head into midweek and beyond due to the uncertainty with the
timing/strength with the upcoming low pressure systems as they
track towards the Southwest/Southcentral regions.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Heavy Freezing Spray 121 139 185.
Gale warning 170 172 173 174 175 176 177 178

&&

$$

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...DS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PEPE
LONG TERM...PD
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