Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Fri Sep 14 2018

Valid 12Z Tue Sep 18 2018 - 12Z Sat Sep 22 2018

Upper ridging centered across the Bering Sea is expected to
gradually flatten through the medium range, although models differ
on exactly how quickly this will occur, with implication for the
flow pattern across Alaska by mid to late next week. Models also
show a relatively small-scale but energetic area of Arctic
shortwave energy affecting portions of Alaska by the middle of
next week, but with fairly significant differences as to the exact
evolution of the feature. Latest trends among the deterministic
guidance has been to keep this energy a bit farther north, but
solutions have waffled between this idea and an alternative of
digging the wave farther south across Alaska, potentially all the
way to the Gulf. Finally, models show somewhat better consensus
with a larger scale upper trough expected to amplify and move from
eastern Asia into the Bering Sea by late next week. While
consensus is good on the existence of this feature, spread is
fairly high with respect to the details, largely the result of the
flattening (or lack thereof) of the upper ridge across the
Aleutians and into southern mainland Alaska. No definitive outlier
solutions were observed among the guidance, and thus a multi-model
blend approach to the forecast was used at the beginning of the
forecast period (Tue), with a trend toward heavier weighting of
ECENS/GEFS means from day 6 (Thu) onward. In general, this pattern
should favor near to above average temperatures across most of
Alaska, with relatively dry conditions through much of next week.
Precipitation chances should increase across the Aleutians and
toward western mainland Alaska by late next week as the
aforementioned system crosses the Bering Sea, but confidence in
the timing is relatively low.

Ryan


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