Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
119 PM EDT Sun Oct 28 2018

Valid 12Z Thu Nov 01 2018 - 12Z Mon Nov 05 2018

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


...Guidance and Predictability Assessment...

Recent deterministic model runs continue to exhibit greater than
normal run to run variance through medium range time scales. In
contrast, recent GEFS and ECMWF ensemble means have been showing
much better run to run continuity. Accordingly, The WPC Alaskan
medium range product suite was primarily derived from a composite
blend of the 06 UTC GEFS mean, 00 UTC ECMWF ensemble mean and the
12 UTC NBM. Large scale flow evolution seems consistent, but
forecast confidence for embedded system details remain much more
problematic given model and individual ensemble members forecast
spread.

...Weather/Hazards Highlights...

Upper level troughing over northeast Russia/Arctic Ocean and
undercutting shortwave impules moving through the Bering Sea and
into northwest and northern Alaska will support swaths of snow
into later week prior to uncertain height rises over the region.

Underneath, a main storm track will steer a series of deepened low
pressure systems from along/south of the Aleutians/AK peninsula to
the northern Gulf of Alaska midweek into next weekend. Lead
moisture inflow will periodically be reinforced with low and
associated frontal system approaches to fuel theats of heavy
precipitation from the Aleutians to the Alaskan
peninsula/Southwest Alaska to especially southern and southeastern
Alaska in a region of most prolonged onshore fetch/lift. Favored
terrain will be most susseptable along with coastal communities
and maritime interests.

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