Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
406 PM EDT Tue Sep 11 2018

Valid 12Z Sat Sep 15 2018 - 12Z Wed Sep 19 2018

...Guidance/Uncertainty Assessment...

The strong upper ridge that has remained a fixture over Alaska
will finally break down by the end of the weekend. However, some
of the ridge still stays in tact over eastern Alaska. This will
lead to a series of shortwaves moving across the Bering Sea, the
Aleutians and western Alaska through most of the medium range
period. Height falls will track across the Aleutians and guidance
is still showing a more amplified solution.  As the low pressure
system moves into western Alaska by late in the weekend, the upper
ridge will shift over the eastern portions of the state--which
will eventually break down as a deep low near the Arctic pushes
southward over northern Alaska by early next week. By midweek, the
amplified pattern continues with lower height falls over eastern
Alaska and another ridge building in from the west over the
Aleutians.  The 12Z GFS/00Z ECMWF were in agreement over the
initial short wave impacting western Alaska over the weekend.
Beyond that, increased the usage of the 06Z GEFS/00Z ECENS due to
uncertainty in the details in the day 6-8 time range.


...Weather Highlights/Hazards...

In the beginning of the medium range, temperatures start out
fairly mild with highs in the mid 50s to low 60s for the Aleutians
and most of Alaska--with temperatures in the mid 40s in northern
Alaska. Arctic air will begin to spill in particularly in northern
Alaska by day 7/day 8 as that system from the Arctic moves across
this area. Low temperatures especially in the higher terrain will
get down into the low 20s/upper teens by day 8. Highest chances of
precipitation will be in the beginning of the forecast period
along the Aleutians and western Alaska with the first system
moving across the Bering Sea. By late weekend and into next week,
the entire state can expect an increase of precipitation. With
these precipitation chances, some higher elevation snow could also
be possible.


Reinhart



WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can be found at:

http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
http://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html