Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
524 PM EST Sat Nov 20 2021
Valid 12Z Wed Nov 24 2021 - 12Z Sun Nov 28 2021
***Very cold over much of the Interior and heavy precipitation
likely for southeast portions of the state***
...Overview and Guidance Evaluation/Preferences...
The 12Z deterministic guidance and ensemble means are in good
agreement with a strong and cold upper low over the southern
mainland through the end of next week, with multiple shortwave
perturbations crossing south of the Aleutians and the Gulf region.
By Friday and into next weekend, models differences are more
apparent with the next storm system crossing south of the
Aleutians, with the CMC farther south compared to the ensemble
means. By the end of the forecast period, model differences are
pronounced over the northern Pacific with respect to a potentially
powerful low pressure system entering the Gulf, with the GFS
considerably stronger and faster and the ECMWF a bit slower and a
little weaker. The CMC is not favored given its depiction of a
ridge axis over the same general vicinity. The WPC forecast was
primarily based from a ECMWF/GFS/UKMET blend through Thursday, and
then GFS/ECMWF and increasing use of the ensemble means through
next weekend.
...Weather/Hazard Highlights...
One of the main things that will make weather headlines will be
the bitterly cold temperatures for this early in the season across
much of the mainland as Old Man Winter makes an early arrival,
with the greatest temperature anomalies of 10-20+ degrees below
normal for western and southern portions of the Interior with
subzero high temperatures likely for many areas, with mainly dry
conditions expected. The other thing will be heavy snow and high
winds for the coastal mountain ranges from the Kenai Peninsula to
the southeast Panhandle, and heavy rain for areas near sea level,
mainly for the second half of the work week. Periods of strong
winds are also likely for much of the Aleutians with a tight
pressure gradient in place owing to intense storm systems passing
to the south.
Hamrick
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