Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
201 PM EDT Mon Aug 20 2018

Valid 12Z Fri Aug 24 2018 - 12Z Tue Aug 28 2018

...Guidance/Predictabilty Assessment and Weather Threats...

Models and ensembles overall offer near average agreement with the
larger scale flow pattern evolution affecting Alaska into next
week, but embedded weather features offer ample forecast spread. A
blend of reasonably clustered 12 UTC GFS and latest GEFS/ECMWF
ensembles seems reasonable Friday into Satuday. A blend of latest
GEFS/ECMWF ensembles was used to derive the WPC medium range
product suite later weekend to next week amid growing uncertainty.
The Canadian and Canadian/NAEFS ensembles show less flow
amplification with time that offers a bigger change to WPC
continuity. Flow amplification makes sense downstream from Soulik
and the entrainment to the west-central Pacific middle to higher
latitudes of the extratropical low associated with Cimaron.

In this pattern, a potent cyclone and focus for high
winds/waves/rainfall will track over the Bering Sea to make
landfall into western Alaska and interior Friday into the weekend.
Lead energy transfers supports triple point low developments
downstream to the northern Gulf of Alaska with inflow and
precipitation to effect southern/southeast Alaska. Forecast spread
is especially problematic for system impacts with potentially
deepened lows to amplify and lift from the northern Pacific to
threaten the Aleutians/Bering Sea then western Alaska, yet the
overall flow will be stormy this 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