Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
147 PM EDT Tue Jul 31 2018

Valid 12Z Sat Aug 04 2018 - 12Z Wed Aug 08 2018

Medium range period will be driven by a strong upper high south of
the central Aleutians that may start to flatten by Monday.  An
upper low is forecast to drift slowly southward through The Last
Frontier.  Outside the 12z GFS, the models/ensembles were in good
agreement on the pattern evolution.  The 500 hPa heights, wind
grids, and pressures were based on a blend of the 00z UKMET, 00z
Canadian, 06z GFS, and 00z ECMWF for Friday night into Saturday
night before using increasing amounts of the 00z ECMWF ensemble
mean and 00z NAEFS mean thereafter, eventually becoming 50% of the
blend.  The remainder of the grids were half deterministic and
half ensemble mean through the period to account for the usually
greater temperature and precipitation chance uncertainty.

Pattern will be rather wet for the panhandle near and east of a
persistent upper trough where onshore flow should continue through
the period, with an initial onslaught of heavy rain Friday and
Saturday as a deep layer cyclone parallels the coast
southeastward.  The next system will slip eastward through the
Bering into western Alaska with another push of precipitation
widespread but fairly light associated with a weak shortwave
passing under the base of the closed low.  Temperatures should be
seasonably mild through the period.

Roth

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