Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
314 PM EDT Thu Oct 04 2018

Valid 12Z Mon Oct 08 2018 - 12Z Fri Oct 12 2018

The stagnant trough/ridge upper pattern is forecast to remain
locked in place through the end of next week but it appears it may
start to relax by next Friday. The upstream ridge over Japan is
forecast to weaken which would allow for zonal flow west of the
Dateline late in the period as the Bering upper low slowly fills.
The models/ensembles remain mostly in agreement on the overall
stuck pattern but disagree on the timing of the embedded systems,
including the future ex-Kong-rey (currently a tropical storm
recurving between South Korea and Japan).

With the good agreement between the GEFS and ECMWF ensembles
(though much less detailed), opted again to use that agreement as
a basis which aligned best with the 00Z ECMWF and Canadian. The
12Z GFS was different enough from the ensembles and ECMWF/Canadian
(and its earlier 00Z/06Z runs) that is was removed from the blend
after Monday but it could not totally be discounted. This was
close to continuity but modified the frontal timing as there was
better consensus with the extratropical transition of Kong-rey
(quicker). There remains lingering uncertainty around Sun/Mon in
northeastern Alaska with a lost upper low that may or may not
float around the AK/Canada border before slipping southeastward.
The ECMWF/Canadian have been more persistent in keeping this over
Alaska while the GFS has not. Ensembles seem to support the
ECMWF/Canadian idea.

This will be a fairly wet pattern for the eastern Aleutians into
southwestern Alaska as the mid-level flow becomes southerly.
Precipitable water values may rise to +2 to +3 sigma next week and
the GEFS M-Climate relative QPF was about the 98th-99th percentile
by next Tue-Thu (with some "MAX" values that were not there 24 hrs
ago). Temperatures will generally be above average due to the
strong ridging except for the Panhandle with the flow mostly out
of western Canada.

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