Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
625 PM EST Mon Dec 21 2020
Valid 12Z Fri Dec 25 2020 - 12Z Tue Dec 29 2020
...Guidance and Uncertainty Assessment...
Overall, the global model ensemble means agree fairly well through
the medium range period. A large and intense cyclone is forecast
to move across the Aleutians into the Bering Sea during the
weekend. This system is well presented by the ensemble means with
good consistency. Nevertheless, the deterministic solutions
indicate more uncertainties. The 00Z ECMWF solution appears to be
most reasonable since it shows good continuity and is most
compatible with the 12Z GEFS/00Z EC mean. However, the 12Z ECMWF
seems to have difficulties handling the system as it deviates
further and further from the ensemble mean solutions with time.
For the early part of the period, deterministic solutions suggest
that a couple of relatively compact cyclones will likely brush up
the southern coasts on Christmas Day--one just off the coast of
the Alaska Panhandle, the other one across the Alaska Peninsula.
The WPC forecast charts for Alaska were constructed based on a
general blend of the 12Z GEFS and 00Z EC mean together with the
06Z and 12Z GFS, the 00Z ECMWF, and some 12Z ECMWF early in the
forecast period. More ensemble means were used later in the
period.
...Weather/Hazards Highlights...
The forecast period should begin with a couple of smaller scale
cyclones forecast to bring periods of enhanced precipitation and
stronger winds across/near the Alaska Peninsula and Alaska
Panhandle on Christmas Day. These cyclones should weaken
considerably on Saturday as the next large scale cyclone is
forecast to intensify and track toward the Aleutians, where gale
to storm force winds and periods of heavy precipitation appear
likely through the Christmas holiday weekend. The system should
slowly weaken early next week as it spreads moderate precipitation
across the Alaska Peninsula. Across mainland Alaska, milder than
average temperatures will prevail through the weekend before
gradually cooling down to near normal levels for both the northern
and southern portions of the state.
Kong
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can also be
found at:
https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html