Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
343 PM EDT Wed Jun 20 2018

Valid 12Z Sun Jun 24 2018 - 12Z Thu Jun 28 2018

Uncertainty remains high, especially across the Aleutians and the
Bering Sea, through Day 8 next Thursday as multiple disturbances
both from the south and the north could potentially converge over
the vicinity.  Ensemble means from major global models basically
depict two scenarios regarding the interaction of a couple of
upper-level vortices near the Bering Sea.  Scenario 1: The GEFS
shows that a new vortex tracking northeastward from the Pacific
will merge with and then expand the old occluded vortex over the
Bering Sea.  Scenario 2: The EC mean and Canadian ensemble mean
indicate the old occluded vortex will dissipate over the Bering
Sea before the new vortex from the Pacific moves along the
Aleutians.  The 12Z ECMWF even shows a third scenario in which a
polar vortex from Arctic Ocean gets involved later in the period. 
In any event, expect highly changeable weather to persist across
the Aleutians and Bering Sea into western Alaska through the
middle of next week.  Meanwhile, more stable weather can be
expected for the rest of Alaska with occasional showers inland
while damp and rainy weather will persist down the Alaska
Panhandle.

The WPC Alaska forecast grids are based on a blend of the 00Z EC
mean and the 06Z GEFS mean mixing in with the deterministic 00Z
ECMWF, the 06Z and the 12Z GFS.

Kong


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
www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html