Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
245 PM EST Wed Feb 06 2019

Valid 12Z Sun Feb 10 2019 - 12Z Thu Feb 14 2019

Today's guidance has held onto the established theme of the
general pattern, with east-central Pacific mean ridging aloft
extending into Mainland Alaska and northwestern Canada for a
decent portion of the period.  A series of systems most likely
tracking over the northwestern half of the Bering Sea will bring
periods of strong winds/high waves and locally significant
precipitation to areas from the Aleutians into the western
mainland/southern coastal areas.  Most models/means suggest that
the mean ridge axis may rebuild a little farther west--centered
more over the mainland versus including part of northwestern
Canada--toward the mid-late part of next week.

During the first half of the period there are two prominent
uncertainties.  One involves the specifics of shortwave energy
likely splitting immediately after early day 4 Sun, especially the
portion that descends over the northeastern Pacific in the form of
a closed low per operational guidance.  Through the 06Z cycle only
the 00Z ECMWF mean has started to resolve this feature among the
ensemble means, while other solutions range between a farther
southwest cluster of the 00Z ECMWF/GFS/CMC and 06Z FV3 GFS and the
slower/eastward 12Z GFS.  The other focus is the deep Bering storm
that may track over or near the far northwestern corner of the
mainland by around the middle of the period.  General consensus
has adjusted somewhat faster than yesterday's continuity but the
track spread seems to be narrowing with a most likely path close
to the Bering Strait and then continuing to the east-northeast. 
The ECMWF mean continues to be the most stable individual solution
for this storm while the 12Z GFS has favorably adjusted a bit
faster than 00-06Z runs that were slowest among operational
solutions.  Overall prefer to start with components of the 00Z
ECMWF/ECMWF mean/CMC and 12Z GFS/06Z FV3 GFS to yield an
intermediate solution for the northeastern Pacific feature and
best consensus/detail for the Bering storm. 

With the passage of the Bering system, operational runs are
hinting that shearing energy aloft may briefly suppress the mean
ridge over the mainland to a slightly greater extent than the
ECMWF/CMC ensemble means around Tue-Wed.  However in the wake of
this energy there is again prominent clustering among the 00Z
ECMWF/CMC and their means toward stronger rebuilding of the mean
ridge by day 8 Thu.  By days 7-8 Wed-Thu individual models and
ensembles diverge regarding the next area(s) of low pressure
reaching the western Pacific/Bering Sea, with a variety of
possibilities for whether features may focus near the core of the
mean trough aloft or along leading flow.  Thus far the ensemble
means have provided the most stable and agreeable solution with a
consolidated system.  While the 06Z GEFS mean was not favored for
its weaker downstream ridge, it does have the strongest ensemble
mean solution for the system entering the western Bering.  The
composite of late-period preferences led the forecast to
transition toward the ensemble means with the 00Z ECMWF mean
having highest weight and 06Z GEFS/00Z NAEFS means given lesser
influence.  Manual adjustments deepened the Bering system and its
leading wind field relative to the initial result of the blend.

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