Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
234 PM EST Mon Dec 17 2018

Valid 12Z Fri Dec 21 2018 - 12Z Tue Dec 25 2018

Models and ensembles continue to advertise a semi-blocky pattern
during the medium range period (Fri - Tues) with the main feature
being an upper low slowly retrograding from western Alaska on
Friday, into northeastern Russia this weekend. Within this overall
flow, several highs and lows rotate through which at the surface
results in several low pressure systems moving eastward south of
the Aleutians and into the Gulf, with lots of uncertainty in the
details. The deterministic models continue to struggle with timing
and details of individual shortwaves, especially past day 5 with
run-to-run continuity rather poor. The ensembles are at least a
bit better, though naturally less defined with systems. The blend
for this cycle of the WPC Alaska progs favored a majority 06z
GFS/00z ECMWF blend days 4-5, with increasing weighting of the
ensembles means (06z GEFS/00z ECENS) beyond day 5. This blend
maintains good continuity with the yesterdays continuity as well.

Temperatures should slowly rise through the period across much of
the state (but especially eastern parts) as heights build and
surface temperatures creep upwards, but Western Alaska may stay
below to well below average underneath the upper trough into next
week. Precipitation looks to favor eastern Aleutians to the
Panhandle given the storm track, with modest amounts through much
of the period. Models focus most of the QPF into coastal British
Columbia to the far southern Peninsula near the triple point of
any given system.

Santorelli/Fracasso


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