Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
543 am akst Thursday Feb 11 2016
Analysis and upper levels...
A broad upper level trough spans from the Gulf to the southern and
eastern Bering and is centered 600 miles south of Kodiak Island.
A strong shortwave can be clearly seen on satellite pinwheeling
around the center...heading west-northwest across the southern
Gulf toward Kodiak Island. Across southcentral...an amplified
ridge is beginning to break down as the strong shortwave pushes
energy toward the northeast Gulf Coast. A steady shield of
moderate precipitation continues ahead of the surface and upper
level feature over the western Gulf as it moves west toward
Over the northern Mainland...a deepening upper level low is
drifting west...with a shortwave disturbance rotating south and
east toward the Yukon-Kuskokwim Delta Region. Out west...a very
broad and complex upper level low system centered about 750 miles
south-southwest of Attu is moving east-northeast in the general
direction of the central and eastern Aleutians.
An active weather pattern continues with nearly daily systems
moving north through the northeast Pacific around the upper level
low centered south of Kodiak. The low over the Gulf today will
move to near Bristol Bay and stall...while interacting with the
low over the northern Mainland and the approaching broad and
complex low moving across the North Pacific. This will help form
one very broad and complex upper level low pressure/trough over
the entire Bering region this weekend.
Meanwhile...the next disturbance to move north on the east side of
the trough will move into the southern Gulf this evening...then
inland over southcentral Alaska sometime later Friday or Friday
night...with the ec the fastest and the GFS and NAM the slowest in
The NAM and GFS were largely preferred for the morning forecast
Short term forecast southcentral Alaska (days 1 and 2)...
the wet and warm pattern continues as broad troughing remains out
west. Multiple lows will rotate through the trough towards the
southcentral from the south over the next couple days all bringing
more precipitation with them. Most of the precipitation will stay
on the Gulf side but some may spill over the coastal mountains as
upper level shortwaves move through. It will also remain warm
enough for many places to see rain as temperatures remain well
above seasonal averages around southcentral Alaska. For places
along the Knik Arm in the morning the rain poses a concern of
becoming freezing rain. Temperatures in the area are below
freezing and the warmer air is overrunning the colder airmass.
Short term forecast southwest Alaska (days 1 and 2...Thursday and
a fairly strong front is pushing up against the Gulf Coast
stretching down toward Kodiak this morning. It is associated with
another weakening low tracking northwest through the Gulf. This is
helping to push some precipitation up against the west side of the
Aleutian Range and keeping scattered showers going down through
the Alaska Peninsula. Given that this low track is slightly
further north...more of the moisture associated with it will make
it inland later today. A fairly Stout upper level low is
positioned over the northern half of the state. These two lows
will work in tandem to create a stretching axis over portions of
the southwest today. This should lead to a band of precipitation
forming just west of the Alaska Range. This band will works its
way slowly west into early Friday morning before falling apart.
This looks to be the best chance of accumulating snow that many
places have seen for several days. By middle-day Friday...this band will
fall apart near or east of Bethel. After this feature...except
just some scattered showers and patchy fog in weak flow to start
Short term forecast Bering Sea/Aleutians (days 1 and 2...Thursday and
relatively quiet weather continues. Much of the north and
eastern Bering will be under the influence of some gusty northeast
flow coming off the Mainland. One weak low spinning south of the
western Aleutians will continue to diminish as another "triple
point" low from the North Pacific takes shape south of Atka Friday.
This low will drift north and sync up with the northeast flow
further north. This will make for a fairly widespread area of
at least small craft level winds across the central Aleutians
heading into the weekend. This system will also bring up another
round of warmer air and rain. It won't be until you reach the far
western Aleutians or the Pribilof Islands that you would find any
snow mixing in.
Long term forecast (days 3 through 7)...
The midterm is highlighted by a complex area of low pressure
hovering along the central and eastern Aleutians with another area
of low pressure moving into the northern Gulf of Alaska. The
complex low near the Aleutians will be on a weakening trend as it
slowly drifts northward into Bristol Bay over the weekend as the
jet energy (steering currents) remains much further south in the
North Pacific. This will continue to bring rain showers (maybe
mixed with snow toward the western aleutians) as well as another
push of warmer air from the subtropics. The low and its associated
front in the northern Gulf will bring rain showers to the northern
Gulf Coast and some snow showers further inland to locations like
Valdez and Thompson Pass. Anchorage and the mat-su valleys look to
remain on the dry side as the front weakens as it approaches the
Gulf Coast and enough cross barrier flow should keep the low
levels too dry to support precipitation.
Heading into the extended period the forecast becomes much more
complicated as model solutions begin to diverge due to the
location and strength of the upper level jet. The GFS is by far
the strongest of all deterministic guidance as it places the jet
further north and allows this just energy to spin up a strong low
in the western Bering Sea behind the departing trough on Tuesday.
The European model (ecmwf) looks to keep this jet energy further south which causes
the low in the Bering to be a good bit weaker and faster as the
further south jet causes the synoptic pattern to be more progressive.
Regardless of the solution...a much more active pattern looks in
store for next week across much of Alaska. Temperatures look to
remain a good bit above normal through Wednesday but models hint
at cooler temperatures taking over by the end of next week.
public...Freezing Rain Advisory 101 111
marine...gale 119 130 138 139 351 352
heavy freezing spray 180 185
Synopsis and model discussion...cirrocumulus
southwest Alaska/Bering Sea/Aleutians...MO