Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
519 PM EST Sun Nov 21 2021
Valid 12Z Thu Nov 25 2021 - 12Z Mon Nov 29 2021
***Arctic cold over much of the Interior and rain/snow likely for
southeast portions of the state***
...Overview and Guidance Evaluation/Preferences...
The weather pattern will be featured with a broad and nearly
stationary upper low situated over the southern mainland of
Alaska, with multiple shortwaves and surface lows pivoting around
the southern periphery of this low across the North Pacific and
the Gulf of Alaska.
Some timing differences are apparent as early as Thursday with
shortwave energy rotating around the main upper level gyre over
southern Alaska, with the CMC a bit more progressive and the GFS
slightly slower, and good overall agreement on the location of the
main upper low. By Saturday, the models struggle with shortwave
and frontal timing over the northern Pacific and Gulf region, with
the CMC appearing to deviate the most from the ensemble means, and
the GFS slower than usual with its progression. There is still a
signal for a strong storm over the southern Gulf by next Monday,
although much uncertainty remains with placement and timing. One
of the more confident aspects of the forecast is that the upper
low/trough over mainland Alaska will be stubborn to move with the
downstream ridge remaining in place across western Canada. The
WPC forecast was primarily based from a ECMWF/GFS/UKMET blend
through Friday, and then GFS/ECMWF and increasing use of the
ensemble means through next weekend and into Monday.
...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 15-25 degrees below
normal for western and southern portions of the Interior with
widespread subzero high temperatures likely. With the exception
for some isolated snow showers, mainly dry conditions are expected
across most of the Interior and North Slope. The other thing of
note 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 the
central and western 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