Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
120 PM EST Sun Dec 23 2018

Valid 12Z Thu Dec 27 2018 - 12Z Mon Dec 31 2018

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

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

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


...Weather/Threats Highlights...

A series of organized low pressure systems and fronts will track
along/south of the Aleutians and the Alaska Peninsula to the
northern Gulf of Alaska into later this week. These lows present a
maritime hazard in the form of high winds/wave and 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 threat will be enhanced into
coastal communities and with heavy snows over favored southern
tier terrain. Expect mainly cold and dry conditions overtop in
this pattern for most of the North Slope/Interior, but uncertain
shortwave energy aloft may support limited light snows. There is
also an increasingly strong guidance signal to then develop a
large closed low/trough aloft that would support development of
potentially quite deep low and stormy conditions into the
Aleutians/Bering Sea Friday-Saturday with lead effects/threats
also spreading to the AKpen/Southwest Alaska and southern Alaska
days 7/8.

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