Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
342 PM EDT Mon Jul 09 2018

Valid 12Z Fri Jul 13 2018 - 12Z Tue Jul 17 2018

Models/ensembles continue to show improved consensus surrounding
the merged upper low expected to be in place across the southern
Bering Sea at the start of day 4 (Fri). Ensemble members over the
past day have shown a trend toward a somewhat slower eastward
progression of this system across the Gulf of Alaska by Sun. The
GFS has not shown this trend, and is the fastest of the
deterministic guidance to bring the upper low into Southeast
Alaska by Sun-Mon, while the consensus holds the feature back over
the Gulf. In the wake of this feature, models show another
shortwave/upper low approaching the Aleutians early next week,
with variations among the guidance in terms of both timing and
strength of the feature. Farther north, models continue to suggest
that the North Slope and perhaps northern portions of the interior
will be subject to intrusion of Arctic shortwave energy this
weekend into early next week, with a couple potential waves. As is
typical of features originating at these very high latitudes,
model solutions show some significant variability in terms of both
timing and amplitude, with run-to-run inconsistencies as well.
Given the generally good agreement early in the medium range, the
WPC forecast for days 4-5 was based on a majority deterministic
blend including the 00Z ECMWF and 12Z GFS. The GFS was discarded
after that due to its fast solution with the system over the Gulf
and the described trend in the opposite direction. Thus, the
forecast from day 6 onward was based on a ECMWF/ECENS/GEFS blend,
with more weight placed toward the ECWMF/ECENS solutions relative
to the GEFS.

In terms of sensible weather impacts, this pattern will result in
a period of near to below average temperatures. The southern half
of mainland Alaska will see good chances for precipitation Fri
into Sun, with gusty winds near the coast, as the Bering Sea
frontal system crosses the region. By Sun into Mon, precipitation
chances may begin to increase across the North Slope as the Arctic
shortwave and associated surface cold front approach.

Ryan


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