Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
233 PM EST Fri Nov 16 2018

Valid 12Z Tue Nov 20 2018 - 12Z Sat Nov 24 2018

The overall synoptic pattern across Alaska for the Day 4 (Tuesday)
to Day 8 (Saturday) time period features initial troughing in the
Gulf being reinforced by a second shortwave moving across the
Bering Sea and into southern Alaska. A couple of shortwaves track
across the Aleutians late in the period as upper level ridging
begins to build into the Gulf on day 8. The overall storm track
features a series of surface lows/fronts tracking mainly across
the Aleutians and into the Gulf south of the mainland.

There is fairly good agreement in the beginning of the period
between the operational models (namely the 06z GFS/00z ECMWF/00z
CMC) along with the ensemble means in the overall synoptic
pattern. By day 6 however, differences in both timing and details
of individual systems/closed lows begin to arise in the
operational models resulting in varying strength/placements of
surface lows crossing the Aleutians into the Gulf. Despite minor
timing differences, there's fairly good agreement between the
latest runs of the GEFS and ECENS ensemble means. The blend for
this cycle of the WPC Alaska 500mb and pressure/fronts progs uses
a mostly operational GFS/ECMWF blend on day 4 and into day 5,
transitioning to a mostly ensemble mean blend (between the
GEFS/ECENS) through day 8. From day 6 onward, used a slight bias
towards the GEFS mean (which is just a hair faster with troughing
in the northeast Pacific and upstream) to fit better with
continuity over the CONUS region downstream. And even through day
8, did opt to maintain very small percentages of the operational
GFS/ECMWF in the blend to keep a little bit of detail in the
forecast and avoid the washed out flow provided by the ensemble
means (presumably a result of large differences in individual
members). This overall blend fits fairly well with yesterdays
continuity over Alaska as well. 

Regarding sensible weather impacts...showery activity may linger
along the Panhandle region through the week as systems track into
the Gulf. The rest of the state will be in a general drying and
cooling pattern as upper ridging slides through across the
Aleutians and the Panhandle and broad troughing sticks over the
mainland. Above normal temperatures on Day 4 across the majority
of the state should transition to near or below normal by the end
of the week and weekend.

Santorelli

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