Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
231 PM EST Thu Feb 07 2019

Valid 12Z Mon Feb 11 2019 - 12Z Fri Feb 15 2019

Latest guidance continues to suggest that the longer-term mean
ridge initially extending from the northeastern Pacific into
Mainland Alaska/northwestern Canada will likely rebuild somewhat
westward by later in the week toward an axis over the western half
of the mainland.  As this evolution occurs the pattern favoring
northeastward-moving lows over the northwestern Bering Sea,
progressive frontal passages farther south/east, and periodic Gulf
waves should transition toward one that keeps low pressure
confined more over the western half of the Bering while high
pressure strengthens over the mainland and northwestern Canada. 
For individual features embedded within the mean flow, operational
guidance in the 00-06Z cycle has generally come into better
agreement compared to previous days and allowed for greater
inclusion of individual models in the forecast to improve detail
depiction (to the extent of maintaining about half weight relative
to means by day 8 Fri).  However ongoing adjustments suggest there
is a risk that the final destination has not yet been reached.

For about the first half of the week the dominant system of note
will be a strong storm tracking across the northwestern Bering Sea
and then close to the Bering Strait and northeastward into the
Arctic.  This storm will likely bring strong winds/high waves and
focused precipitation from the Bering Sea/Aleutians into the
western mainland.  After the majority cluster trended faster
yesterday, it has reverted back to timing more similar to two days
ago.  Aside from timing adjustments the ECMWF mean has remained
the most stable individual solution for overall track while the
GEFS mean has had the least probable weaker/southeast solution. 
GFS runs have occasionally been a little to the southeast of
consensus as well in the Tue-Wed time frame but latest runs
compare more favorably.

Over the Gulf of Alaska on Mon guidance has been very diverse and
erratic with energy that may form a closed low and surface system.
 00-06Z guidance jumped to a northern solution which had been
advertised by yesterday's 06-12Z GFS runs but the 12Z GFS went to
the south of prior ECMWF/ECMWF mean runs that had served as a
reasonable compromise.  Preferred a majority blend (with only
minority input from the 12Z GFS) to provide enhanced detail but
with below average confidence.

Immediately behind the strong Bering storm, operational guidance
has held onto the idea of another shortwave crossing the
mainland/Gulf around Wed.  Among the means the GEFS mean has been
reflecting this feature while the ECMWF/CMC means have been slow
to catch onto it.  There is a reasonable signal in the guidance of
a corresponding short-lived northern Gulf surface wave.

By days 7-8 Thu-Fri guidance agrees on the general theme of low
pressure over the western Bering but not on the number of lows. 
Overall the GFS/CMC and their means suggest two progressive lows
in contrast to the 00Z ECMWF/ECMWF mean that have a single slower
moving low.  Prior ECMWF means showed more evidence of the second
low though.  A multi-model/ensemble mean blend ultimately led to
two waves timed about a day apart--perhaps a little close together
but more representative of established progression than the slow
scenario.  Farther eastward the GEFS mean has trended noticeably
stronger with the upper ridge that builds into the mainland,
providing better agreement with other solutions than was the case
yesterday. 

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