Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
320 PM EDT Sat Nov 03 2018

Valid 12Z Wed Nov 07 2018 - 12Z Sun Nov 11 2018

Given the spread and run-run changes seen among the guidance
yesterday, it is not surprising that today's consensus offers
significant adjustments for some aspects of the forecast while
major spread persists for other aspects.  There is still good
enough clustering among latest operational models to recommend a
compromise among the 00Z GFS/FV3 GFS/ECMWF/CMC for the early part
of the forecast Wed-Thu.  Then by the latter half of the period,
the models and ensemble means loosely form two separate
clusters--leading to a preference that trends toward incorporating
20 percent total ensemble mean input (06Z GEFS/00Z ECMWF mean) for
day 6 Fri and 60 percent for days 7-8 Sat-Sun.

Over the Bering Sea recent guidance has trended strongly toward
the idea that leading energy flowing into the region should
ultimately wrap up a fairly strong storm system mid-late week. 
This is in contrast to earlier solutions that were all over the
place for what the leading energy would produce in the way of a
surface reflection while showing more of a signal toward a
northwestern/northern Bering storm toward Fri-Sat.  While there is
decent agreement upon this mid-late week storm there is still a
fair amount of latitude spread for track, with the 06Z GFS
straying to the southern side of the spread by day 6 Fri while the
00Z CMC mean is extremely far north.  The 00Z GFS/FV3
GFS/ECMWF/CMC provided the best combination of detail and track in
light of the ECMWF mean still being a bit farther north than
operational runs.  Trailing energy which guidance had used to
develop the previously forecast northern Bering system now appears
more likely to flow around the southwestern periphery of the
leading system's overall circulation.  There may well be a defined
wave associated with this energy for some period of time but there
is currently too much spread to depict very strongly in the
forecast.

During the latter half of the period the operational models and
ensemble means sort themselves into two primary clusters with
respect to the amplitude/sharpness of the trough-ridge pattern
dominating much of the forecast domain from near 170W to western
Canada.  Specifically the models show a deeper/sharper upper
pattern that ultimately supports the progression of a deepening
southern mid-latitude wave and moisture which ultimately reach the
Gulf of Alaska next weekend.  The broader and less amplified
ridge-trough configuration in the means would result in less
mid-latitude interaction.  The 06Z GEFS mean has a hint of the
operational scenario though.  The sharpening trend aloft versus
yesterday is quite apparent in the means by day 8 Sun so it seems
reasonable to use a model/mean compromise as the best single
starting point.

Regarding somewhat less contentious parts of the forecast...
Trends over the past couple days have favored the northern half of
the spread for the system tracking into the Gulf of Alaska.  The
06Z/12Z GFS runs have gone counter to this trend with a track
somewhat south of the 00Z GFS and other operational models as well
as the means.  The 00Z ECMWF is a bit on the northwestern side of
the guidance envelope but certainly worth including as part of the
forecast given the trends.  Meanwhile short range northern
Bering/eastern Siberia low pressure has trended faster/farther
northward compared to yesterday's dominant guidance cluster as it
tracks into the Arctic.

The combination of mid-late week system and possible late period
system(s)/leading moist flow yields a signal for highest 5-day
precipitation totals extending from near the Kenai Peninsula and
Alaska Panhandle.  Locations near the Aleutians may see a period
of strong winds depending on the exact track of the system
forecast to track across the Bering Sea during the latter half of
the week.

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