Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
524 PM EST Tue Dec 22 2020
Valid 12Z Sat Dec 26 2020 - 12Z Wed Dec 30 2020
...Guidance and Uncertainty Assessment...
For the forecast period, global deterministic and ensemble
guidance shows relatively good agreement and consistency from the
previous cycle. A intense and large cyclone is expected to track
across the Aleutians into the Bering Sea this weekend. This system
shows very good agreement in the 12Z guidance
(ECMWF/GFS/CMC/UKMET) with respect to its depth and location. As
that system weakens and occludes, several additional shortwaves
will track in the fast flow underneath it where the deterministic
models show timing and strength differences to various waves of
low pressure. By this point, the WPC blend used an increasing
amount of the ECENS/GEFS to dampen out the uncertainty and to keep
some component of continuity in the day 6-8 period.
...Weather/Hazards Highlights...
The aforementioned large scale cyclone is forecast to intensify
and track toward the Aleutians, where gale to storm force winds
and periods of heavy precipitation may be possible 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.
Taylor
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