Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
600 PM EST Sun Dec 19 2021
Valid 12Z Thu Dec 23 2021 - 12Z Mon Dec 27 2021
...Overview...
The extended range over Alaska (Thursday-Monday) will be dominated
by a blocky and anomalously strong upper level ridge and surface
high pressure over the northeast Pacific. Multiple
shortwaves/storm systems will try to track around the western and
northern periphery of the high, but nothing strong enough to break
it down significantly through the period. Episodes of light to
moderate snow are expected across portions of the mainland.
...Overview and Guidance Evaluation...
The latest models and ensembles continue to show excellent
agreement on the large scale blocky pattern holding strong through
at least next weekend. The main model uncertainties arise from
various shortwaves attempting to round the top of the ridge into
northern Alaska. There are indications a shortwave may try to
erode the northern part of the ridge some late in the period but
plenty of differences with regards to timing and strength. Todays
WPC forecast used a blend of the deterministic guidance for days
4-5, increasing the ensemble means by the last half of the
forecast period to help mitigate these smaller scale differences
which may still take several days to resolve fully.
...Weather/Hazard Highlights...
With strong ridging in place over the Gulf/North Pacific, no areas
of heavy precipitation are currently expected over the southern
coast and Panhandle region. Some light to moderate snow is
possible across mainly western portions of Alaska associated with
systems attempting to push inland from the Bering Sea. Areas of
light to moderate precipitation are also likely across western
portions of the Aleutians ahead of a couple of cold front
attempting to cross the island chain. Below normal temperatures
across the eastern portion (especially the Northeast) of Alaska
should moderate somewhat through the weekend except across parts
of the Panhandle which could be 20 to 30+ degrees below normal.
Santorelli
Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards outlook 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