Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
430 PM akst Friday Feb 12 2016
Analysis and upper levels...
there is an upper level low and its associated surface low over
the northern Gulf moving towards the northwest. There is another
upper wave over the Alaska Peninsula with a weak surface
reflection over Kodiak Island. There is a large upper low centered
south of the Aleutians with an elongated east-west oriented front
along 50 degrees north latitude. A surface low is forming along
the eastern portion of this front well south of the Alaska
Peninsula. High pressure is centered over the northern Bering
the numerical models are in decent agreement. The one feature they
seem to be struggling with is the low developing along the front
south of the Alaska Peninsula. As this low works its way towards
Kodiak Island on Saturday the models are a bit split on where the
surface low GOES. The European model (ecmwf) is furthest east with this low with
the center forecast to pass east of Kodiak Island Saturday night.
The other models are more clustered...putting the low over Kodiak
or even to the west of it...although timing is a little different.
Forecast confidence is thus a bit below normal with this feature
but near to above normal otherwise.
Short term forecast southcentral Alaska (days 1 and 2)...
a trough lifting northward from the Gulf will bring showers to
inland portions of southcentral Alaska late tonight into early
Saturday morning as downslope flow temporarily weakens. The main
forecast challenge will be determining precipitation type as
surface temperatures hover near freezing and a warm layer persists
aloft as noted on the Anchorage afternoon sounding. Currently
expecting a mix of rain and snow from Anchorage towards the
Matanuska Valley and all snow moving into the Susitna Valley. A
few patches of light freezing rain will also be possible into
Saturday morning in locations where temperatures are slower to
climb above freezing. Overall...any precipitation that falls
should remain light and help to limit any major impacts...with no
accumulation expected. Showers will then come to an end during the
morning as the trough exits to the north. Precipitation will
remain largely focused along the Gulf Coast for the rest of the
weekend as onshore flow continues and another front approaches the
area Saturday night. Another weak upper wave will bring a renewed
chance for a few showers across inland locations on Sunday.
Short term forecast southwest Alaska (days 1 and 2)...
the Kuskokwim Delta has a weak disturbance moving through that
will produce scattered snow showers this evening. While the
Aleutian Range will have moisture spilling-over from the low
pressure system that is tracking to the northern Gulf tonight.
By Saturday the next North Pacific low will track just south of
Kodiak Island before tracking into the Shelikof Strait region by
Saturday evening. This will produce gusty easterly winds along
the Aleutian Range accompanied by moisture advecting into the
Bristol Bay interior before spilling over into the Kuskokwim
Delta. The temperatures will be in the middle 30s in the Bristol
Bay region except for upper 30s along the Aleutian Range. While
the high temperatures through the Kuskokwim Delta Region will be
in the middle 20s heading into the weekend.
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
broad easterly flow over the Bering will keep weather throughout
much of the area quiet through Saturday. A front associated with a
North Pacific low approaching the akpen will then clip the
eastern Aleutians/akpen Saturday...bringing some gale force winds
through Shelikof Strait and along the Pacific side of the akpen.
Long term forecast (days 3 through 7)...
Starting Monday the persistent pattern of a broad trough over the
Bering with ridging over the western North American coast will
begin to break down as a cold upper level trough begins to dive
into the Bering. This will allow for a shift to northwesterly flow
aloft...bringing cold air back to the Mainland/Bering Sea as a
series of cold lows move into the area. The first will come from
the Kamchatka into the Bering Sea...and the other from the
Beaufort Sea into the northern interior. The first system looks
to impact the Bering Sea with gale force winds and snow/rain on
Mon-Tue...while weak high pressure over the Mainland should bring
sunny skies and cooler temperatures.
The models then begin to diverge on this system by the middle of
the week...introducing uncertainty in how it will impact the
southern Mainland. The 12 and 18z GFS runs in particular are strong
outliers by causing most of the energy to dive well south of the
aor and deepen...bringing little in the way of precipitation to
the area and instead an outflow event for the Gulf Coast.
Meanwhile the rest of the models and current wpc guidance keep a
low and associated front in the Gulf...bringing rain/snow to the
Gulf Coast and mostly downsloping to southcentral. As a result it
appears that most of the precipitation next week should occur over
the Bering and Gulf Coast...with little in the way of chances in
ending the snow drought for the lower elevations of southcentral.
Synopsis and model discussion...bl
southwest Alaska/Bering Sea/Aleutians...period