Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
143 PM EST Tue Dec 18 2018

Valid 12Z Sat Dec 22 2018 - 12Z Wed Dec 26 2018

...Guidance/Predictability Assessment and Preference...

Models and ensembles offer a reasonably similar larger scale
pattern evolution over the next week, but differ significantly
with the amplitude and timing of embedded small-mid scale systems
days 4-8. Accordingly decided after coordination with Alaskan NWS
weather forecast offices to primarily derive the WPC medium range
Alaskan forecast from a blend of the compatable 06/12 UTC GEFS
means and 00 UTC NAEFS/ECMWF ensemble means along with healthy
input from the National Blend of Models. This solution maintains
max WPC continuity.

...Weather/Threats Highlights...

A main storm track over the next week will include a series of
organized low pressure systems and associated frontal systems that
track along/south of the Aleutians and the Alaska Peninsula
into/across the Gulf of Alaska. These lows present both a maritime
hazard and a periodic heavy precipitation threat throughout the
next week for the Aleutians/AKpen and southern/southeastern
Alaska. Individual system timing and strength is variable in
guidancem but the overall storm track offers good predictablity.
In this pattern, a lead system over the northern Gulf of Alaska
this weekend is quickly replaced upstream with another set of lows
from just to the south of the Aleutians to back into the Gulf this
weekend and especially into early-mid next week.

Overtop, guidance is more uncertain with depiction of the pattern
over the North Slope/Interior and Bering Sea days 4-8. However,
shortwave trough/closed low energy aloft tends to favor a weakness
aloft from northwest Alaska to the Bering Strait and northern
Bering Sea. This may support some light snows.   

Schichtel


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