Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
330 PM EDT Thu Aug 30 2018

Valid 12Z Mon Sep 03 2018 - 12Z Fri Sep 07 2018

The upper flow over much of the Northern Hemisphere will likely
either remain or become quite amplified next week in part due to
the extratropical transition of Typhoon Jebi through Japan. The
deterministic models diverge in details but at least clustered in
principle toward a highly amplified or cutoff pattern as a lead
upper low drifts along 45-50N south of the Gulf and another drops
southward across the eastern Aleutians. The ensembles were quite
varied in their track of Jebi and thus the axes of the downstream
ridge/trough couplet west/east of the Dateline, respectively,
which results in a broad ensemble mean trough. Given the
likelihood of a strongly meridional pattern, opted to rely more on
the nearest deterministic model which was the 00Z ECMWF. 12Z GFS
was also close later in the period after the lead upper low drifts
far enough south out of the area. 00Z Canadian was somewhat near
the ECMWF as well which shows a slow progression of the two
systems near/south of the Aleutians. This would result in ridging
poking up into western Alaska but this may be tempered by northern
stream energy attempting to squash the ridge (seen as a couple
fronts through the North Slope). With so many moving parts, opted
to allow at least some relaxation of the ridge but surface high
pressure will mostly dominate the interior and southwest mainland
next week.


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