Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
340 PM EDT Thu Jul 26 2018

Valid 12Z Mon Jul 30 2018 - 12Z Fri Aug 03 2018

Amplified pattern across the Pacific will feature an upper low
initially in the Bering Sea next Monday that will slowly but
steadily lift northeastward then drop southeastward through the
week. The ensembles were in good agreement on the evolution
through about next Wednesday before the ensemble systems split E-W
with the trough axis in the Gulf next Thu/Fri. The ECMWF ensemble
mean lied in between the farther east Canadian ensemble mean and
farther west GEFS means (00Z/06Z) and was a closer fit to
continuity and a good middle ground for now. The upstream flow
will be complicated by the west hook movement of tropical storm
Jongdari and a big block to its north so am not too confident of
the downstream flow enough to favor a farther east or west axis,
based on where the ridging will push northward into the Bering
Sea. To the north, flow atop the ridge is still uncertain as a
shortwave may slip east-southeastward (UKMET/ECMWF/Canadian) or
linger along 170W (GFS), which will affect the extent of some QPF.

The 00Z ECMWF paired best with the ensemble means through the
period but the 12Z/06Z GFS were close enough that a 50/30 blend of
those models with a 20% blend of the ensembles formed a good
starting point. Trended toward more ensemble weighting toward next
Wed/Thu as uncertainty increases. This will bring a plume of
moisture into SW Alaska early in the week that will push eastward
in time. This will also push northward through western Alaska as
the dying occlusion gives way to the new sfc low around the Kenai
next Thursday.

Fracasso


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