Scientific Forecaster Discussion
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Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
139 PM akdt Wednesday Apr 16 2014
Analysis and upper levels...
A broad upper level trough extends from Kamchatka to Southeast Alaska
this afternoon. An embedded closed low is over the southern
Bering and Aleutians...with another small low over the southern
Gulf of Alaska. At the surface...a broad area of weak low
pressure covers the the entire forecast area...with a couple of
low centers over the western and eastern Aleutians...the western
Gulf and near Southeast Alaska. The main jet remains well south of
Alaska and is pretty much disassociated from the features
affecting the forecast area. As a result very weak flow aloft is
all that is available for moving around systems. This means
current weather will consist of weak and poorly timed waves of
precipitation moving across the forecast area...separated by
periods of dry conditions with significant breaks in the overcast.
Guidance is in agreement over the western domain for the first
day or so as the Bering and Aleutian lows become absorbed into a
broad trough of low pressure over the eastern Bering and Alaska
Peninsula. This area of low pressure remains more or less over the
same area into Sat...and the forecast is handled fairly well with
the GFS. The story is different over the eastern domain as the
trajectory of the initial low near Southeast Alaska varies by model.
The ec and NAM bring the low into the Haines Skagway end of the
Panhandle on Thursday...while the GFS brings the low to Yakutat. This
more eastern trajectory of the ec-NAM may be attributed to a
slightly more eastward extension of the upper low during that
time. Since this system mainly affects the Juneau forecast area
where the ec and NAM solutions were preferred...we deferred and
utilized that solution for the eastern domain as well. This model
combination was also applied to the next North Pacific low. This
begins to affect the Gulf with wind Friday afternoon and becomes a
zonally oriented low across the southern Gulf on Sat.
Short term forecast...
Bering Sea/Aleutians...East to northeast flow will be followed by
north flow on Friday and northwest on Sat. Isolated to scattered
rain and snow showers can be expected through Sat.
Southwest Alaska...scattered rain and snow showers will persist
through Sat as cyclonic flow persists across the region.
Southcentral Alaska...inland areas will have mainly dry
conditions...except for mountain rain and snow showers...until
the second low moves inland Thursday night into Friday. The associated
trough will spread more widespread precipitation inland into Sat.
High pressure then will build over the area with drying. Coastal
areas will have plenty of shower activity until high pressure
builds Friday into Sat. The arrival of the second low will bring a
round of rain and small craft to gale force winds through the
Long term forecast...
In the west...high pressure will spread dry conditions across the
region into sun...but a North Pacific low will then spread wind
and rain later sun through middle week as it moves along the southern
side of the Aleutians. In the east...the low pressure near the
Gulf of Alaska remain in the same vicinity with wind and rain
mainly for coastal areas through Monday. Brief drying on Tuesday will be
followed by more shower activity as the Aleutian low arrives on
Ds Apr 14