Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 250023
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
423 PM AKDT SUN JUL 24 2016
.ANALYSIS AND UPPER LEVELS...
The main low is over Southwest Alaska and is slowly tracking south
towards the Alaska Peninsula. Multiple shortwaves are rotating
around this low and bringing rain to areas around Southwest and
Southcentral Alaska. Out west, northwest flow is bringing rain and
cloud cover to the Bering and Aleutians.
The models are in decent agreement with the major features and are
all now picking up on the coastal ridging building in along the
north Gulf coast. However, they are struggling with how strong the
barrier jet will be with this setup. Concerning the main low,
guidance is doing much better with the timing of the primary
shortwaves but they are struggling with intensity with the hi-res
models predictably showing stronger waves. Hi-res guidance was
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The broad upper level over the southwest mainland will halt it`s
easterly progression towards Southcentral this evening, as the
upper level ridge to the east stands firmly over the eastern
portion of the Southern Mainland through monday night. A series
of weak waves continue to eject northward over the area, along
with persistent diffluent flow aloft. This will keep rain and/or
widespread showers in the forecast for much of the area through
Monday night. By Tuesday morning, a second lobe of upper level
energy will track northward into the Northern Gulf, reinforcing
the wet conditions over the area through Tuesday afternoon.
While an unsettled pattern will remain in place across the area
over the next several days, a coastal ridge and associated low
level jet will build along the northern Gulf Coast. This will help
to support local gusts through Turnagain Arm and the Copper River,
and help to support some local downsloping in the Anchorage Bowl
and Kenai Peninsula.
A wet pattern will remain in place through Tuesday, as the upper
level low stalls over the western portion of Southcentral this
evening, and eventually is pushed southward into the North
Pacific by the blocking ridge building across the Gulf of Alaska.
As the pressure gradient builds between these two features,
locally terrain driven gusts will develop. The strongest winds are
anticipated mainly along Turnagain Arm Monday afternoon and
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The upper low will keep a showery regime over the southwest
mainland through the early part of the work week as it sinks
slowly southward into Bristol Bay tonight and then remains in the
vicinity of the Alaska Peninsula through Tuesday. A moist and
relatively unstable air mass in the wake of the low will support
isolated thunderstorms across much of the area this evening, and
possibly into the overnight hours over portions of the Kuskokwim
Valley. Showers will diminish in coverage at times through Tuesday
as the low moves away from the area, particularly over the
Kuskokwim Delta. However, a pair of easterly waves rotating
around the northern periphery of the low will bring increases in
shower coverage each afternoon, with diurnal heating helping to
generate enough instability to support a slight chance of
thunderstorms during the afternoon/evening through Tuesday.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The low dropping southward across the Alaska Peninsula will keep
the heaviest shower activity confined to the southeast Bering
through Tuesday, with broad northerly flow and weak upper level
ridging moving in over the remainder of the Bering. This will
support largely benign conditions dominated by cloudy skies and
patchy fog through Tuesday.
.LONG TERM FORECAST (Days 3 through 7)...
The upper levels have a closed low over the Shumagin Islands with
support from a 90 knot westerly jet streak located south of the
Eastern Aleutians late Tuesday. The jet stream will transition to
a southwesterly flow streaking into the southern portion of the
Southeast Panhandle by late Wednesday night. By Thursday the upper
level low will be camped out in the northern Gulf before exiting
the region into the Yukon Territory. This will bring a wetter
pattern with shortwaves tracking through the region with the
southwesterly flow. Meanwhile, the western/central Bering is
influenced by the high pressure west of the Shemya accompanied by
widespread marine layer stratus/fog heading into early Friday.
The Southwest Alaska region will see a showery weather regime as
an inverted trough associated with the closed low south of the
Shumagin Islands as this feature tracks into the Gulf. The Bristol
Bay and the Lower Kuskokwim Valley will be affected by this
feature through Thursday. By Thursday morning a trough swings
through from the north over the Y-K Delta moving eastward. By
Friday morning this trough swings through the Southcentral region
with more numerous showers heading into the weekend. Upstream,
westerly flow will reside over the Bering, and the
Southwest/Southcentral regions through the weekend. There will be
multiple shortwaves with this flow bringing a showery weather
regime through the weekend.
SYNOPSIS AND MODEL DISCUSSION...dk
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...cb