Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
229 PM EDT Tue Jun 19 2018

Valid 12Z Sat Jun 23 2018 - 12Z Wed Jun 27 2018

Expect some persistence of mean troughing over the extreme western
mainland and eastern Bering Sea, with continued uncertainty over
the position and depth of an embedded upper low.  There is
somewhat better agreement for a system tracking across the
northeastern Pacific, with arrival of upper support helping to
erode the downstream ridge initially extending from western Canada
into parts of central Alaska.  At the same time anticipate mean
troughing over the Arctic with an average of most similar guidance
tending to place the northwestern mainland near the southeast
periphery of the mean trough.  Over recent days guidance has been
having considerable difficulty in resolving forecast details
across the western-central Pacific and the Aleutians, as upper low
energy over Asia in the short range emerges over the northwestern
Pacific and leading flow evolves toward a progressive/low
amplitude pattern.

The WPC forecast was initially based on a majority of the
deterministic ECMWF and GFS, along with some of the CMC for Day 4
(Saturday).  Given increasing model spread across the Aleutians
and over the Arctic, more of the EC and GEFS mean was incorporated
for the second half of the forecast period.

Hamrick


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