Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
209 PM EST Thu Dec 27 2018

Valid 12Z Mon Dec 31 2018 - 12Z Fri Jan 04 2019

Models and ensembles show broad agreement at the large scale
across Alaska during the extended period, but solutions become
much more chaotic and variable at smaller scales. An active and
progressive flow pattern across the North Pacific will gradually
erode broad upper-level ridging across western North America,
lowering heights somewhat across eastern/southeastern Alaska,
although at least some degree of ridge axis should remain in place
through the period. The result will be broad southwesterly flow
across the Gulf of Alaska with an active storm track and numerous
shortwaves/low pressure systems.

Clustering of ensemble member and deterministic solutions
initially on day 4 (Mon) suggests that a deep and relatively
compact surface low should be located in the eastern Bering Sea or
Bristol Bay. The ECMWF and FV3 were the closest deterministic
solutions to this consensus, and thus were heavily weighted in the
forecast on day 4. Any semblance of clustering of solutions
diminishes quickly from day 5 (Tue) onward, and individual model
solutions also become much more variable from run-to-run. A
majority ensemble mean (ECENS/GEFS) based forecast from Tue onward
supports the idea of a rapid succession of low pressure systems in
continued southwesterly mid/upper-level flow, with another low
pressure system entering the Gulf Mon night/Tue and another by
late Thu/early Fri.


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