Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
200 PM akdt Sat Oct 25 2014
Analysis and upper levels...
an elongated upper low that stretches from far eastern Russia to
just off the Arctic coast of Alaska is creating zonal flow aloft
over the entire Bering Sea and southern Alaska today. There are
some short wave disturbances in this flow which are bringing some
ares of precipitation across southern Alaska as well. The first is
over the Copper River basin and another is associated with a
weakening front that is moving through the Kuskokwim Delta this
The polar jet is running off far northern Japan to Kamchatka and
then through the northern Bering Sea just south of the upper level
low. The location of the jet is important as it is what will
rapidly strengthen a surface low currently north of Attu and move
it near St Lawrence Island by Sunday evening.
There is another surface low weakening near the Bering Strait this
afternoon which is the low from which the front over the
Kuskokwim Delta emanates. The weak surface low persists near
Middleton Island as it has since early Friday. This low will
slowly move eastward over the next day and then finally dissipate
models are in much better agreement today in regards to the strong
low that will be moving into the Bering Sea tomorrow. Although
they are in better agreement with each other they are all showing
a significant change in low track than what any of them showed
yesterday. Instead of moving the low into the Chukchi Sea the
models are all stopping its northern progress near St Lawrence
Island Sunday afternoon and then keeping it stationary through
Monday before moving it southeastward and weakening it as it heads
toward Bristol Bay. The models are having some problems resolving
the track of the low during its weakening phase as it heads
southeast but they are all taking the general movement of it in
that direction and that is a large difference from yesterday.
Short term forecast...
the upper level disturbance over the Copper River has been slow to
move eastward and out of the area but it should by early this
evening which will end the snow that has been falling since
yesterday. There will likely be some low clouds and fog that linger
over the basin through tomorrow morning.
The low near Middleton Island continues to produce some bands of
rain and snow showers along the north Gulf Coast but these showers
will continues to weaken and cover less area through the night as
the low weakens and moves eastward. There are still some gusty gap
winds near Whittier and Seward due to this low. These winds should
also diminish during the evening as the low pulls away from the
area. The Cook Inlet and Susitna Valley areas should see some
large areas of clearing overnight. Clouds packed up along the
chugach and Talkeetna Mountains should dissipate as drier air
moves into the region. There is a chance for some low clouds and
fog to develop near the inlet late tonight if enough dry air does
not make it into southcentral.
the weakening front moving through the Kuskokwim Delta today will
move into the Kuskokwim valley and Bristol Bay area overnight.
Precipitation will diminish as this system moves eastward as well.
There is an abrupt wind shift with this front with south winds
ahead of it to northwest winds behind it. The strong low moving
into the Bering Sea will eventually bring another chance of
precipitation to the Kuskokwim Delta by Sunday night.
the low north of Attu will rapidly strengthen over the next day
as it moves rapidly toward St Lawrence Island. This will bring a
large area of gale force winds and some storm force winds to the
Bering Sea as it moves through the area. While precipitation will
be rain as it begins and then turns to snow showers after the cold
air wraps around the low from the northwest.
Long term forecast...
While the models are continuing to struggle with the track of a
developing low from the Gulf into the North Pacific through the
middle of next week...the general long term pattern remains
largely unchanged. A long wave trough extending from the West
Coast into the akpenn on Monday will dissipate and form a cutoff
low over the extreme southern Gulf by Wednesday. This will allow
for ridging to spread throughout much of the Mainland...keeping
conditions dry with near to below normal temperatures through the
middle of next week. There is also a possibility that this period
of quiet weather for the Mainland could continue through the work
Out west...there remains very good agreement in the timing of an
Aleutian low that will begin moving through the western Aleutians
on late Tuesday. This system will then spread into the central
Bering by late in the work week...keeping cloudy skies with a
chance of rain for the region through the work week.
Due to the fairly large uncertainty in the low track through the
Gulf and North Pacific from Tuesday into Thursday...the long term
forecast once again heavily used wpc guidance. This keeps the low
track mostly to the south of the aor...treating the further north
track towards the north Gulf Coast from previous runs of the GFS
as an outlier. The ec and GFS ensemble means have been relatively
consistent with this low track...leading to increased confidence
in quiet weather moving into the southern Mainland by middle week.
Marine...gale 178 181. Storm 185.