Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
224 PM EST Sat Dec 22 2018

Valid 12Z Wed Dec 26 2018 - 12Z Sun Dec 30 2018

...A Widespread Heavy Precipitation Threat for the Alaskan
Southern Tier...

...Guidance/Predictability Assessment and Preferences...

Ensemble means seem to offer a similar pattern evolution next
week, but deterministic guidance still differs significantly with
the amplitude and timing of embedded small-mid scale systems days
4-8. Accordingly decided to primarily derive the WPC medium range
Alaskan forecast product suite from a blend of reasonably
compatable GEFS/NAEFS/ECMWF ensemble means along with some input
from the National Blend of Models.


...Weather/Threats Highlights...

A main storm track mid-later next week includes a series of
organized low pressure systems and fronts that track along/south
of the Aleutians and the Alaska Peninsula into the Gulf of Alaska.
These lows present a maritime hazard in the form of gale to storm
force winds and a periodic heavy precipitation threat for the
Aleutians/AK peninsula/Southwest Alaska and southern/southeastern
Alaska. Individual system timing/strength remain quite variable in
guidance, but the overall storm track seems reasonable. The lows
are expected to increasingly effect the full southern tier of
Alaska as well as the Bering Sea/western Alaska and the Gulf of
Alaska with pattern amplification. Stormy conditions including
widespread heavy to excessive precipitation will channel into the
state between a supporting mean troughs aloft and a building mean
downstream upper ridge. The threat will be enhanced into coastal
communities and with heavy snows over favored southern tier
terrain. Otherwise, expect mainly cold and dry conditions over
much of the North Slope/Interior, but uncertain shortwave energy
aloft may support some limited 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