Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 280013
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
413 PM AKDT MON JUN 27 2016
.ANALYSIS AND UPPER LEVELS...
Low pressure across the western Bering Sea is losing any
upper level support and is starting to slowly weaken to the
northwest of Shemya. Draping from this low is an occluded front
that stretches to the southeast, between Shemya and Attu Island.
High pressure across the central Bering Sea and Aleutian
chain is continuing to weaken and slide to the southeast this
afternoon. 11 to 3.9 micron satellite imagery depicts a rather
robust area of fog and stratus in this region. AKPEN and Bering
Sea upper air analysis continue to depict strong inversions near
the surface that has been evident for the last few days now.
Across the southern Gulf of Alaska is an ever persistent
vertically stacked low. Several disturbances will rotate around
this low and be key players in weather across much of the region
throughout the week.
Much like the last few days - the models remain in good
agreement through the short term. Minor timing differences
begin to emerge into the Wednesday afternoon time frame at
the surface. The ever present surface low that has been spinning
in the Gulf of Alaska, for quite some time, will weaken and get
absorbed into a surface trough diving down across the Aleutian
Chain. When looking into the upper levels we begin to see more
differences in timing of events expected across the area. A fairly
potent shortwave can be seen in water vapor imagery rounding the
base of the stacked low. This shortwave will wrap around the low
eventually making it into Gulf of Alaska forecast. A much more
potent wiggle in the flow will move from east to west across the
Copper River Basin and into the Susitna Valley Thursday afternoon
and evening. The ECMWF and Canadian seem to be the most strongest
and most aggressive while remaining farther north. The American
models are a little less aggressive and farther north. Regardless
- a much wetter mid to end of week is looking on tap at this
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)... The
thermal trough remains to our north, and will move farther to the
northwest. This synoptic feature combined with the ridge building
from the Southeast Panhandle into the Copper River Basin will
inhibit any developing thunderstorms in the AOR through Tuesday.
Meanwhile, the low in the Gulf remains almost stationary with
southeasterly flow transporting moisture, and precipitation into
the northern Gulf coastal communities. Therefore, the Anchorage
Bowl, and the Susitna Valley will enjoy sunny skies through the
early evening before receiving increased cloud cover. The
Southcentral region will have a showery weather regime with the
Anchorage Bowl, and the Western Kenai having drier conditions due
to down-sloping. Look for the gap winds to remain gusty through
the Turnagain Arm, Knik Arm, and the Copper River Valley through
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
An unstable environment will continue for Southwest Alaska into
Thursday. There is also just enough capping for enough potential
energy for thunderstorms to develop in the afternoon and evening
hours. This is especially true in the Kuskokwim Valley and
surrounding mountains. However, the instability is not impressive
enough for more than widely scattered thunderstorms. The other
concern is fog out over the Eastern Bering that will move in over
coastal areas overnight and then dissipate by the afternoon. That
pattern will continue into Thursday.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Ridging over the Central Bering is slowly tracking east as it
weakens. Underneath the ridging fog is impacting areas over the
Bering, Aleutians, and Alaska Peninsula. As the ridging weakens
into Tuesday the fog will also lighten, but still remain through
Wednesday. Behind the ridge, a front is moving through the Western
Bering towards the Central Bering. On Tuesday the front will stall
near the Pribilof Islands where it will remain into Thursday.
.LONG TERM FORECAST (Days 3 through 7)...
The extended forecast beginning late week will feature a a large
upper low over the western Bering Sea and another stretching
across the Gulf of Alaska. Narrow ridging (and the associated
thermal low) will be centered over the interior of Alaska north of
the Alaska Range. This will mean easterly flow aloft will be
present across southern Alaska. These patterns can be conducive
to inland heavy rain events as thermal lows forming across the
Yukon interact with shortwave troughs embedded within the trough
before retrograding west. There is currently low certainty with
timing and exact placement of these lows as they move west, but
there is increasing confidence that large parts of southern Alaska
will potentially see moderate to heavy rain and shower events
Thursday through Saturday. The best chances for heavier rains will
be along and near the Alaska Range, with lesser chances farther
south. After Saturday, the Gulf trough will weaken and move east
with the Bering trough moving in and replacing it. This will keep
a wetter and more moist pattern in place with periods of rain
along the coast and shower threats inland.
SYNOPSIS AND MODEL DISCUSSION...SS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK