Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
314 PM EST Sun Dec 30 2018

Valid 12Z Thu Jan 03 2019 - 12Z Mon Jan 07 2019

Ensemble means continue to show consensus on the general flow
pattern evolution in the vicinity of Alaska during the extended
period. An upper ridge axis initially across western Canada during
the short range will be quickly eroded by a rapid succession of
shortwave energy from the North Pacific, 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.

Deterministic solutions continue to vary from run-to-run. Thus, a
very similar approach was taken to the forecast as yesterday. The
ECMWF continued to be reasonably well clustered with the ensemble
consensus (represented by the ECENS and NAEFS) through much of the
period. The ECENS and NAEFS were favored over the GEFS as the GEFS
has continued to be the most variable and has performed generally
poorly with the flow across the North Pacific recently. A 50/50
deterministic/ensemble blend was used on day 4 (Thu), with a
gradual shift to heavier ensemble mean weighting through the
duration of the forecast period.


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