Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
310 PM EST Mon Nov 05 2018

Valid 12Z Fri Nov 09 2018 - 12Z Tue Nov 13 2018

The majority of today's guidance continues to show a strong signal
for significant amplification/sharpening during the period.  The
best consensus has strong shortwave/closed low energy over and
south of the extreme western Bering Sea as of early Fri digging
into a potentially negatively tilted trough with embedded closed
low southwest of Mainland Alaska while downstream eastern Pacific
ridging builds into western Canada and likely to some degree over
Mainland Alaska.  This pattern should bring a significant increase
of moisture/precipitation into the Gulf of Alaska and southern
coastal/Panhandle regions.  However there are still notable
minority solutions that are less pronounced with the pattern
evolution.  Even among the consensus solutions the model/ensemble
spread is significant for some embedded details.

As for potential surface systems associated with this evolution,
one is a North Pacific wave that may strengthen as it tracks into
the southeastern Bering or eastern Aleutians/Alaska Peninsula. 
There is a general indication of this system but still not great
clustering for track/depth.  Even with the uncertainty for this
feature, guidance spread has been much greater over recent days
for a leading east-central Pacific mid-latitude system.  Depending
on exactly how flow aloft evolves, solutions have ranged from
bringing it into or just west of the Gulf of Alaska or tracking it
south of the Panhandle.  Today the operational models are still
widely dispersed but the ensemble means are starting to show a
greater probability that this wave will track within the western
part of the full envelope from recent days and become incorporated
into the overall mean low that may settle near or south of the
Alaska Peninsula.  This scenario is certainly plausible given the
amplified nature of evolving pattern.

Elsewhere, there is decent clustering for initial low pressure
over the northern Bering Sea as of early day 4 Fri.  After that
time there is still some spread for exactly where it tracks before
low pressure emphasis transfers farther south.  Over recent days
the ensemble means had been somewhat ahead of the operational runs
in showing a fairly far northward track with this system.  Across
the Arctic, guidance shows differences in specifics but in general
the flow aloft looks fairly nondescript with one or more surface
highs separated by modest weaknesses/troughs.

Within the more likely cluster for the evolving large scale
pattern--involving latest GFS/ECMWF runs and their means--recent
multi-day trends alone would suggest a tilt toward the more
westward ECMWF/ECMWF mean.  However the continued existence of the
flatter/more progressive CMC scenario and a slight eastward
adjustment in the 12Z GFS make it difficult to go more than only a
fraction closer to the ECMWF/ECMWF mean.  The forecast blend
started with mostly 06Z GFS and 00Z ECMWF/UKMET for days 4-5
Fri-Sat followed by increasing 06Z GEFS/00Z ECMWF mean weight to
50-80 percent over the days 6-8 Sun-Tue period.  Minority input of
the 00Z ECMWF continued through day 8 and 06Z GFS through day 7.  

The most consistent signal for enhanced precipitation extends from
the Kenai Peninsula through the Panhandle, though the past day's
trends in the ECMWF/ECMWF mean would extend this area back to
parts of the Alaska Peninsula.  Some areas of strong winds will be
possible around low pressure systems.  There is lower confidence
in where/when strongest winds would occur due to ongoing spread
for depth/track of individual surface lows.

Rausch


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