Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
242 PM EDT Mon Jul 30 2018

Valid 12Z Fri Aug 03 2018 - 12Z Tue Aug 07 2018

Medium range period will be driven by a strong upper high south of
the central Aleutians that may start to flatten by next Tuesday.
Troughing will linger over the northern 1/3 of Alaska as a lead
upper low digs into the Gulf Fri/Sat and then slowly southeastward
toward Haida Gwaii. The models/ensembles were in good agreement
overall on the pattern evolution with the most agreement around
the upper high and less agreement on how the pattern north of 60N
unfolds as the previous runs have not been that consistent. In
addition, the recent GFS runs were displaced a bit farther south
in the far southeast Gulf compared to most of the ensembles and
the 00Z ECMWF and Canadian (at least early) along with continuity.
Much of the forecast was based on that consensus with a trend
toward the ECMWF ensemble mean (plurality of the forecast) and the
00Z ECMWF along with the 06Z GEFS mean. Question by next week is
how the ridging relaxes across the Bering as the ensembles showed
no consensus on that (thus a preference for the middle ground
ECMWF ensemble mean).

Pattern will be rather wet for the panhandle as the upper low
slowly sinks southeastward and the surface occlusion/front push
into British Columbia. Again, how much precipitation falls will
depend on how far south the system digs -- ECMWF was wetter than
the GFS. Next system will slip eastward through the Bering into
western Alaska with another push of precipitation (widespread but
fairly light despite a defined moisture tap from the central
Pacific. Increasingly zonal flow should limit higher amounts.
Temperatures will cool behind the lead and weakening secondary
boundary with only a weak warm-up ahead of the Bering system next
Sun/Mon.


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