Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
230 PM EST Tue Feb 05 2019

Valid 12Z Sat Feb 09 2019 - 12Z Wed Feb 13 2019

Most guidance agrees that the large scale mean pattern will favor
ridging that extends from northeastern Pacific through Mainland
Alaska and northwestern Canada, downstream from an axis of
troughing/embedded upper lows from the far northwestern Pacific
across portions of the Bering Sea and Siberia.  This regime should
lead to a series of strong low pressure systems that track
over/near the northwest half of the Bering Sea while associated
frontal systems head into the western mainland but weaken as they
encounter the mean ridge aloft.  These features will bring
periodic enhancement of winds/precipitation across the Aleutians
and into the western mainland and southern coastal areas. 
Strongest wind potential will likely be with the system currently
forecast to track across the Bering and possibly the extreme
northwestern mainland during the first half of next week.

Within the consensus pattern there are some significant
differences of varying scale.  From the larger scale perspective
the most prominent differences involve the strength of the ridge
on a day-to-day basis.  During the first half of the period recent
guidance has been trending stronger, with the 00Z ECMWF mean
providing the best representation of the stronger trend versus
other means.  However the 00Z ECMWF may be overdone as it is so
strong with the northern part of the upper ridge that by Sun-Mon
it diverts northern Pacific shortwave energy much farther
southwest than consensus.  Remaining guidance suggests that this
energy will produce a short-lived Gulf of Alaska wave in this time
frame.  Later in the forecast the ECMWF mean has weakened its
upper ridge a bit over the course of recent runs but it has
support from the 00Z CMC mean for keeping the ridge stronger than
recent GFS/GEFS mean runs.  Going along with this idea of a
stronger ridge aloft closer to the ECMWF mean, would expect early
week Bering Sea low pressure to track farther northwest than the
GEFS mean in particular and to some extent GFS runs.  The 12Z GFS
low track has adjusted somewhat closer to preference than prior
6-hourly runs.  Note that by 12Z Tue the 00Z CMC/06Z FV3 GFS are
on the fast fringe of the ensemble envelope.  Overall recent runs
of the ECMWF mean have provided the most stable solution for the
track of this northwestern Bering system.

Meanwhile as of the start of the period early day 4 Sat, there is
very high uncertainty regarding a possible frontal wave that could
be in the vicinity of the Alaska Peninsula or well north or south
of the area.  Recent ECMWF runs have generally been on their own
in keeping the system well to the south but other solutions vary
greatly on northward timing and there is very little signal for
this feature from the individual ensemble members.  Thus for the
time being the preference is to stay closer to continuity and the
ensemble means.  By day 8 next Wed there is decent agreement in
principle on another system coming into the picture over the
western Pacific and extending its influence into the Aleutians. 
The ensemble means provide a reasonable starting point for
depicting this system in light of operational model spread.

Based on above preferences the forecast blend placed more weight
on the 00Z ECMWF mean than other solutions.  During the first half
of the period the blend included minor components of the 12Z
GFS/06Z GEFS mean/00Z ECMWF/00Z CMC.  By day 8 Wed the blend went
exclusively with ensemble means, 75 percent toward the ECMWF mean.

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