Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
312 PM EDT Mon Oct 29 2018

Valid 12Z Fri Nov 02 2018 - 12Z Tue Nov 06 2018

...Stormy Weather/Heavy Precipitation Threat for the Alaskan
Southern Tier/Maritimes...


...Guidance and Predictability Assessment...

It remains the case that 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 12 UTC GEFS mean,
00 UTC ECMWF ensemble mean and the 12 UTC NBM. Opted to include
measured inout from the 00 UTC ECMWF that of deterministic model
guidance to add a bit more smaller scale detail consistent with
predictability. The ECMWF seemed overall most in line with
ensemble clusterings and continuity. This was coordinated with
local Alaskan weather forecast offices. 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 the Arctic Ocean and undercutting
shortwave impule energy into northwest and northern Alaska may
support lingering modest snows into late week prior to height
rises over the region. Underneath, a main lead storm track will
steer a series of deepened low pressure systems from along/just
south of the Aleutians/AK peninsula to the far northern Gulf of
Alaska midweek late week into next week. 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 then southern
and southeastern Alaska in a region of most prolonged onshore
fetch and lift. Favored terrain will be most susseptable along
with coastal communities and maritime interests. Upstream closed
low/trough energy advance in the Sunday to next Tuesday timeframe
is meanwhile expected to bring a renewed storm development threat
eastward across the Bering Sea, with potential to approach/effect
western Alaska late period.

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