Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
147 PM EST Sat Dec 29 2018

Valid 12Z Wed Jan 02 2019 - 12Z Sun Jan 06 2019

Ensemble means continue to show some consensus on the general flow
pattern evolution in the vicinity of Alaska during the extended
period. An upper ridge axis initially across western Canada on day
4 (Tue) will be quickly eroded by a rapid succession of shortwave
energy from the North Pacific Wed-Thu, before becoming
reestablished by next weekend. This along with persistent negative
height anomalies across the Bering Sea will result in persistent
southwesterly flow for much of Alaska, with a preferred storm
track from the North Pacific into the Gulf of Alaska.

A look at the latest ensemble runs reveals perhaps a modest
increase in spread through much of the extended period (even on
day 4), driven to a large degree by variability among GEFS
members. Additionally, deterministic guidance continued to show
highly variable and inconsistent solutions from run-to-run.
Despite general larger scale agreement, model consensus as
pertains to the details of individual systems is quite poor. As a
result, ECENS and NAEFS ensemble means were the most heavily
weighted solutions in the forecast throughout the extended period.
The ECMWF, moderately well clustered with the ensemble means
through much of the period, comprised a minority component of the
forecast.


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