Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
126 PM EDT Sun Aug 19 2018

Valid 12Z Thu Aug 23 2018 - 12Z Mon Aug 27 2018

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

Guidance offers near average agreement on the synoptic flow
pattern evolution affecting Alaska over the next week, and
embedded weather features offer more forecast spread Friday
onward. A well clustered GFS/ECMWF and their ensembles composite
blend works day 4/Thursday. A blend of latest GEFS/ECMWF ensembles
was then used to derive the WPC medium range product suite after
that amid growing uncertainty. The Canadian and NAEFS ensembles
show less later period flow amplification that would offer a
bigger change to WPC continuity.

In this pattern, a potent cyclone and focus for high
winds/waves/rainfall will track over the Bering Sea to make
landfall into western/southwest Alaska then interior Friday/next
weekend. Lead energy transfers supports triple point low
developments downstream to the northern Gulf of Alaska with
inflow/precipitation to effect southern then southeastern Alaska.
Forecast spread/uncertainty increases into next weekend for system
details and in particular with potentially deepened lows to
amplify then lift over the northern Pacific to threaten the
Aleutians.

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