Scientific Forecaster Discussion
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Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
403 PM akdt Sat Jul 22 2017
Analysis and upper levels...
A large area of high pressure is in control across the Bering Sea
and Mainland Alaska. Over the Bering Sea and Aleutians, this
pattern is continuing the widespread low clouds and fog that is
typical of summertime weather patterns. Over the Mainland,
offshore flow and high pressure add up to a day of sunshine and
warm summertime temperatures for nearly the entire area. Some
early-morning fog in the western Susitna Valley and parts of
southwest Alaska has diminished, though the much more widespread
and substantial area of fog over the Bering is beginning to push
onto the coast of the Yukon-Kuskokwim Delta. This is in response
to increased southwesterly winds that are starting to develop
ahead of a weather front that is taking shape over the far
northern Bering and eastern Russia. With time, this front will
drive straight into the northwest coast of Alaska.
Models are in very good agreement, and none of the models were
removed from consideration today. The NAM is preferred again east
of the Alaska Range due to the higher resolution depiction of
winds through the complex terrain.
panc...VFR conditions will persist throughout the period. A light
sea breeze will develop later this afternoon before diminishing by
Short term forecast southcentral Alaska (days 1 and 2)...
high pressure over southern Alaska will slide south over the next
couple of days. On Sunday a front associated with the polar jet
will approach the Alaska Range and move into the Susitna Valley.
This will bring rain and considerable cloud cover, mainly to the
northern portions of the area. Flow at the lower levels will
switch from offshore to onshore, and become fairly strong later in
the day. As the front moves south Sunday night and Monday, it
will weaken and begin to fall apart.
Short term forecast southwest Alaska...
High pressure over the southwest will break down overnight as a
front associated with an Arctic trough moves inland. Rain
associated with this front will enter the northern Kuskokwim Delta
Sunday morning and move to the interior Bristol Bay area Monday.
Visible satellite imagery shows a marine layer of low stratus and
fog just off the Kuskokwim coast this afternoon. As high pressure
breaks down overnight, strengthening onshore flow will pull this
marine layer inland. This will result in areas of fog along the
Kuskokwim Delta coast tonight. Further southeast, dense fog over
the northern and western Alaska Peninsula this morning has burned
off with daytime heating. However, expect this fog to redevelop
overnight as southwesterly flow resumes over Bristol Bay.
Short term forecast Bering Sea/Aleutians...
A ridge of high pressure aloft is building east over the Bering
Sea this afternoon. Under this ridge the area remains entrenched
in a marine layer of low stratus and fog. Over the next couple of
days the upper level ridge will break down and more progressive,
zonal flow will resume. As the ridge breaks down, a front
currently over the western Bering will progress through the
northern Bering and move to the West Coast by Sunday. With the
ridge holding over the southern Bering and Aleutians, the front
won't enter the southern Bering until Monday. As the front moves
through the northern Bering Sunday and the southern Bering Monday,
it will spread rain and small craft winds over the area. An even
warmer airmass advecting into the western and northern Bering
behind the front will allow the fog and low stratus to remain over
the Aleutians and the Bering for the next few days.
Long term forecast (days 3 through 7)...
The long term period will be very dynamic and progressive. Several
systems will move into the state from the Arctic and the Bering.
With this active pattern in place, expect the ridging over the
Aleutians to get shunted to the west and eventually south.
Sensible weather-wise, anticipate an uptick in precipitation for
the western and south central portions of the state Tuesday night
through Saturday. All the while, the western Aleutians will
be under the influence of the ridge keeping much of the western Bering
dry, however low clouds and fog will persist under the stable air
mass. The European model (ecmwf)...Canadian Gem and GFS models are in relatively
decent agreement with the shift towards a wet dynamic synoptic
pattern through the extended forecast period.