Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
633 PM EST Mon Dec 20 2021
Valid 12Z Fri Dec 24 2021 - 12Z Tue Dec 28 2021
...Overview...
The extended range over Alaska (Friday-Tuesday) will continue to
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. Periods of light snow
will be possible across portions of Western Alaska as these
systems weaken as they track inland.
...Overview and Guidance Evaluation...
The latest models and ensembles continue to show strong consensus
on the large scale blocky pattern holding strong into early next
week. The main model uncertainties arise from various shortwaves
attempting to round the top of the ridge into northern Alaska.
There are indications a couple of shortwaves may try to erode the
northern part of the ridge some this weekend and again early next
week but plenty of differences with regards to timing and
strength. Todays WPC forecast used a blend of the 12z GFS and
ECMWF with increasing GEFS/ECENS ensemble means through the
forecast period to help mitigate the smaller scale differences
which may still take several days to resolve fully. The 12z CMC
and UKMET both seemed too eager to erode the northern parts of the
ridge with a system that drops into northern AK, so those
solutions were not included in the blend for today. The resulting
final blend solution offers a forecast similar to yesterdays
continuity.
...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 fronts moving
across the island chain. A strong pressure gradient setting up
along the southern Coast/northern Panhandle region due to a deep
surface high in the Pacific and deep surface low off the Northwest
U.S. coast may result in the potential for stronger winds near the
coast, particularly early in the period. Above normal temperatures
initially across western parts of the state should creep farther
east through the weekend, with daytime highs as much as 20 degrees
above normal for western and North Slope areas. Parts of the
Panhandle in contrast could be 20 to 30+ degrees below normal
through much of the period.
Santorelli
Hazards:
- High winds across portions of mainland Alaska, Thu-Fri, Dec
23-Dec 24.
- Much below normal temperatures across portions of the Alaska
Panhandle, Mon, Dec 27.
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