Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
219 PM EST Tue Jan 29 2019

Valid 12Z Sat Feb 02 2019 - 12Z Wed Feb 06 2019

Today's guidance is fairly agreeable in showing a mean pattern
that features a ridge over the east-central Pacific into Mainland
Alaska and an area of troughing with one or more closed lows
across the northwestern Pacific and Bering Sea.  The mean ridge
will be somewhat porous, allowing periodic passage of energy
contained within Bering Sea/North Pacific flow.  This pattern will
tend to keep the strongest low pressure systems over the Bering
Sea while leading frontal systems weaken in their approach to the
mainland.  Associated triple point waves may track across the
Alaska Peninsula and Gulf of Alaska.

The dominant system of note to start the period on day 4 Sat will
be strong low pressure over the Bering Sea.  The 00Z GFS had been
on the southeast side of the ensemble envelope--bringing the
system into the southwestern part of the mainland--but succeeding
runs have trended to the 00Z ECMWF/CMC/UKMET that show a track
into the northern Bering Sea/eastern Siberia.  On the other hand,
over the course of the weekend there is a fair degree of spread in
amplitude for initial troughing over northwestern Canada and
eastern Alaska.  The ECMWF and flatter GFS have been persistent
with their respective ideas while other solutions lie between the
two extremes.  The overall guidance average, including the 06Z FV3
GFS that evolves more like the 00Z ECMWF, points toward a scenario
perhaps half to two-thirds toward the amplified side of the
spread.  A days 4-5 blend that starts with the 00Z ECMWF/12Z
GFS/00Z UKMET/00Z CMC (in order of more to less weight) represents
consensus for the Bering Sea system and leans in the desired
direction for the northwestern Canada/eastern Alaska trough.

Confidence is lower in trailing North Pacific/Bering Sea low
pressure and frontal system(s) by the first half of next week,
favoring increased weight of ensemble mean guidance (06Z GEFS/00Z
ECMWF mean) to capture the most agreeable aspects of the mean
pattern including a tendency toward Gulf of Alaska low pressure. 
There is better than average model/mean clustering for a strong
system forecast to track into the western Aleutians by day 8 Wed
so prefer to hold onto about half total weight of operational
model input (12Z GFS/00Z ECMWF) through the end of the forecast to
yield a slightly stronger system than forecast by the ensemble
means.  Slower trend over the past day suggests a blend that tilts
a bit more toward the ECMWF/ECMWF mean relative to the GFS/GEFS
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