Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
241 PM EST Mon Dec 31 2018

Valid 12Z Fri Jan 04 2019 - 12Z Tue Jan 08 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 (in a somewhat weaker form) by the weekend. This
along with persistent negative height anomalies across the Bering
Sea will result in persistent southwesterly flow for much of
southern and southeastern Alaska, with a preferred storm track
from the North Pacific into the Gulf of Alaska. Farther north,
guidance continues to suggest the potential for an upper high to
cut off somewhere near the Bering Strait, which would open
portions of the interior and the North Slope up to drier and
potentially cooler northerly flow.

Deterministic solutions continue to vary from run-to-run. Thus, a
very similar approach was taken to the forecast as the past few
days. 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, which has performed generally poorly with the flow across
the North Pacific recently. A 50/50 deterministic/ensemble blend
was used on day 4 (Fri), 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