Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
356 PM akdt Monday Jul 25 2016
Analysis and upper levels...
the main low over the area is now south of the Alaska Peninsula
which has begun to change the general flow over southcentral
Alaska from south to southeasterly, which factors in for potential
downsloping for areas around Cook Inlet. One of the many
shortwaves rotating around this low is moving through the Gulf
approaching the north Gulf Coast and helping to bring up another
push of moisture. Another shortwave is moving east to west across
southwest Alaska with thermal troughing building in from the
interior over the same area. Out west, northerly flow persists.
for much of the short and mid terms the models are in good
agreement. However, there are a few problems that could result in
an impactful change. One of the problems that arises in the mid
term is the track of the upper low on Wednesday. The NAM, GFS, and
Gem all track the low towards the northern Gulf while the ec keeps
near Kodiak Island. The northern Gulf position seems more likely
in the upper level flow pattern. The other issue in the mid term
is with a shortwave that is pushing south along the West Coast of
the state late on Tuesday. There are a lot of model differences on
the different runs as to what happens with this shortwave as it
interacts with the low south of the Alaska Peninsula. How the
models eventually handle this feature will play into how much rain
areas of the eastern Aleutians and Alaska Peninsula receive.
Short term forecast southcentral Alaska (days 1 and 2)...
an unsettled weather pattern continues across southcentral, with
a broad upper level low tracking through the Alaska Peninsula
continuing to support a moist southeasterly flow over the Gulf
and coastal areas of southcentral. Rainy conditions will continue
across much of southcentral this evening before becoming more
showery overnight, and then transitioning to a downsloping regime
within deep southeasterly flow. Showers will become limited due to
downsloping on the Lee side of the chugach and Kenai ranges
through Tuesday evening. However, the areas along the northern
Gulf Coast will continue to experience rainy conditions and gusty
gap winds through Wednesday afternoon, as the surface coastal
ridge supports the redevelopment of the coastal jet along the
northern Gulf Coast and Prince William Sound. The jet will weaken
again tonight as the wave slowly pushes inland, then redevelop on
both Tuesday and Wednesday as a series of upper level waves
approach the coast.
Short term forecast southwest Alaska (days 1 and 2)...
a showery regime will remain overhead for the next couple days.
Despite the plentiful cloud cover and rain showers, temperatures
will hit or exceed normals in most areas. These showers will be
most active in both intensity and coverage during the afternoon
and evening hours before losing intensity and coverage overnight.
Activity should be most widespread tonight, followed by a
decreasing trend each day. The pattern begins to change Wednesday
afternoon as northwesterly flow pushes in to the Kuskokwim Delta.
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
fairly benign conditions across most of the Bering as weak
northerly flow encompasses the area. Several disturbances aloft
will bring a chance for rain to the central Bering, but nothing
widespread is expected. Areas of dense fog will lie over the
western Bering through the forecast period.
Long term forecast (days 3 through 7)...
the forecast on Thursday and Friday keeps the highest
precipitation amounts along the northern Gulf and Prince William
Sound as an upper low moves east across the southern Gulf. A North
Pacific ridge to the west keeps the Bering and western portion of
the Aleutian chain under low clouds and stratus through much of
the weekend. Model solutions differ heading into Saturday as an
upper low digs from the Arctic. This system is progged to bring a
front into the southwest Friday night. The European model (ecmwf) is currently the
most aggressive solution bringing a very wet pattern to
southcentral Saturday night. In comparison, the GFS would lag the
front across the southwest with a triple point low developing over
the eastern Aleutian chain Saturday night. The forecast in the
extended range was adjusted with the European model (ecmwf) and gefs mean as it
offered the best run to run consistency. Even though this solution
was favored, there is still a bit of uncertainty for rain and wind
Synopsis and model discussion...dk
southwest Alaska/Bering Sea/Aleutians...ml