Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
316 PM EDT Sun May 20 2018

Valid 12Z Thu May 24 2018 - 12Z Mon May 28 2018

An upper low is forecast to slowly but surely move eastward along
53N Thu-Mon, sending a couple fronts eastward into the Panhandle
and western Alaska where upper ridging is forecast to make a
resurgence. The models/ensembles generally have a similar idea
through the medium range, but differ in the evolution of the
Arctic flow north of about 75N and also over the north central
Pacific. With a noticeable difference between the GEFS mean and
the ECMWF ensemble mean and a lack of continuity/agreement between
the GFS/ECMWF deterministic runs with each other or their ensemble
means, opted to use a best consensus for the first few days when
agreement was acceptable before shifting toward maintaining system
progression in a reasonable manner. This resulted in using the 12Z
GFS/00Z ECMWF at first before utilizing the 06Z GFS and then the
00Z GFS as well which was closer to continuity than the 00Z ECMWF.

Still kept the idea of having the lead then secondary front push
into the Gulf and weaken/dissipate late in the week into the
weekend before a system from the north Pacific moves eastward
south of the Aleutians next Sat-Mon. Trend seems to favor ridging
building back to the northwest from NW Canada which should keep
the systems from making much indent eastward. Upstream flow over
northeastern Russia will be in a state of flux, likely resulting
in the differing solutions seen in recent runs. General southwest
to southerly flow will keep southeastern Alaska/Panhandle fairly
wet but not excessively so due to the split flow south of 50N
(upper low off the California/Oregon coast). Temperatures will be
close to average.


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
www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html