Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
609 PM akst sun Feb 7 2016
Analysis and upper levels...
The large-scale upper level pattern over southern Alaska and
adjacent waters remains largely the same this afternoon. The
vertically stacked low over the Gulf is rapidly weakening as a new
low over the North Pacific races eastward on a subtropical jet.
The jet is working to return the flow to a more zonal
pattern...which will ensure a continuation of largely benign
weather for interior southern Alaska. The pattern looks to
continue mainly being dominated by weak features rotating around
the upper low centered south of the Aleutians...as any strong lows
remain coupled with the jet over the Pacific well south of Alaska.
The front moving across the Gulf to the Alaska Peninsula is
producing widespread gales but with only localized storm force
winds around Kodiak Island and the Pacific side of the Alaska
Peninsula. The front is weakening substantially as the vertically
stacked low weakens and the upper level jet support moves away to
the east. Middleton Island radar shows an area of stratiform
precipitation moving into the coast through southern Prince
William Sound...otherwise very little precipitation associated
with the front has been reported elsewhere. High cloudiness is
moving into inland southcentral...with winds now flowing offshore
across all of Cook Inlet in response to the approaching front.
Surface ridging is in place across southwest Alaska keeping skies
mainly clear in areas north of the Alaska Peninsula.
Over to the Aleutians...a strong low being enhanced by a 180 knots
jet is barreling across the North Pacific south of the western
Aleutians. The strong winds and precipitation associated with it
are just beginning to reach the western Aleutians this afternoon.
Very weak features are moving across the remainder of the
Bering...with localized areas of fog and low stratus along with
weak winds the primary weather stories.
The models remain in above average agreement this afternoon.
Nearly all of them support continued weakening of the front and
low moving towards the Alaska Peninsula. Some discrepancies
between the models appear looking towards Monday morning when a
new relatively weak low forms over the northeast Pacific south of
the Gulf...but moves into the Gulf by Monday evening. The ec is
the fastest of the models with the NAM being the slowest. Given
the expectation of relatively low impact from it...the GFS was
chosen as a Happy medium between the other models.
Out west...the ec has been handling the strong low moving towards
the western Aleutians best...and it was the model of choice
concerning the evolution of the low. Forecast confidence is high
given the broad model agreement through the next couple days.
Short term forecast southcentral Alaska (days 1 and 2)...
The vertically stacked low south of Kodiak Island will continue to
gradually fill as it tracks north tonight then crosses the Alaska
Peninsula and moves into Bristol Bay Monday. The associated
frontal system stretching across the western and north Gulf will
move over Kodiak Island...the eastern Kenai Peninsula and Prince
William tonight where it will become stalled through Monday. The
position of the front and track of the low are both favorable for
strong east to southeast gap winds through Turnagain Arm as well
as other similarly oriented terrain gaps. Gusty northeast winds
will continue across Kodiak Island this evening then a shift to
strengthening easterly winds late tonight through Monday morning
as the low passes by the south side of the island. Another weak
area of low pressure will lift into the central and eastern Gulf
Monday afternoon then track north towards Yakutat and Dry Bay
Monday night through Tuesday morning. The next stronger low moving
up from the south will cross 50n around 145w Tuesday afternoon
with the associated frontal system spreading into the southern
Short term forecast southwest Alaska (days 1 and 2)...
a decaying front will move over the Mainland tonight. Initially
tonight the only impact will be an increase in cloud cover along
with the chance for flurries along The Wood River Mountains or
some sprinkles to the east nearer the Aleutian Range. As the front
passes tomorrow...a little more rain is expected from Dillingham
north and west...mixed with snow at higher elevations...and rain
showers east of Dillingham. Winds will turn from the east and get
a little gusty but should be sub-strong wind range. A few showers
will linger on Monday night but a drying and clearing trend will
continue through Tuesday when winds will lighten and turn to the
north. Expect temperatures slightly above normal for this time of
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
mostly benign conditions for most of the Bering Sea with light
winds and isolated to scattered rain/snow showers. However...there
is a front approaching the western/central Aleutians associated
with a strong low pressure system in the northern Pacific. The
gale force front will just make it to the chain and slowly slide
west to east through mid-week. Expect cloudy conditions along the
chain with areas of rain and snow.
Long term forecast (days 3 through 7)...
the long term forecast remains predominantly dry across the
southern Mainland with storms systems continuing to bring active
weather across the southern Bering and Gulf of Alaska. Tuesday
night into Wednesday a low developing across the eastern Pacific
moves a front into the southern Gulf on its track toward the
Alaska Peninsula. Gusty gale winds and rain will spread east to
west across the Gulf with stronger winds possible if a deeper
surface low develops. Gusty winds along channeled coastal terrain
is expected to increase early Wednesday as this next system
tightens the pressure gradient along the northern Gulf. Models
are struggling with how to handle the low as it nears the Alaska
Peninsula Wednesday night as a second closed low in the North
Pacific picks up a faster easterly track on the south side of the
Aleutian chain. Due to this uncertainty in the Middle Range forecast
changes are likely to be made for winds and precipitation across
the western Gulf and the eastern Bering.
Marine...gale 119 120 130 131 132 138 139 150 155 172 174 176 177.
Synopsis and model discussion...jw
southwest Alaska/Bering Sea/Aleutians...mtl