Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
229 PM EST Fri Dec 28 2018

Valid 12Z Tue Jan 01 2019 - 12Z Sat Jan 05 2019

Models and ensembles continue to 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 by Thu-Fri. Ensembles show general agreement that the ridge
axis should become reestablished by next weekend. The result will
be broad southwesterly flow across the Gulf of Alaska with an
active storm track and numerous shortwaves/low pressure systems
throughout the extended forecast period.

Clustering of ensemble member and deterministic solutions
initially on day 4 (Tue) suggests that a relatively deep surface
low should be located near the Kenai Peninsula. The ECMWF and FV3
were the closest deterministic solutions to this consensus, and
thus were heavily weighted in the forecast on day 4. Clustering of
solutions begins to diminish from day 5 (Wed) onward, and
individual model solutions also become more variable from
run-to-run. A majority ensemble mean (ECENS/GEFS) based forecast
from Wed 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 late Thu and
yet another by late Sat.


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