Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
524 PM EST Tue Dec 21 2021
Valid 12Z Sat Dec 25 2021 - 12Z Wed Dec 29 2021
...Overview...
The extended range forecast over Alaska through the middle of next
week 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 are expected
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 12Z model guidance suite remains in excellent overall
agreement on the large and in charge surface/upper level high
centered over the North Pacific near 45N/155W through the entire
forecast period, with perhaps a slightly southward budge by early
next week. The models also strongly suggest a north-south
oriented ridge axis should exist across western mainland Alaska.
The main model differences reside across the Aleutians and the
Bering with the storm system tracking towards the northeast in the
general direction of northwestern Alaska. The strongest signal
for a shortwave will be on Sunday/early Monday across the northern
half of the state as it traverses the northern periphery of the
ridge, with the GFS/CMC indicating a stronger signal. A second
storm approaching the western Aleutians has a greater model
spread, with the 12Z ECMWF much stronger across the Bering by next
Tuesday night and loses ensemble support.
Taking these factors into account, a general deterministic 12Z
model blend should suffice as a starting point through the
upcoming weekend, followed by slightly more of the GFS/CMC than
the ECMWF and increased use of the ensemble means.
...Weather/Hazard Highlights...
A storm system and associated cold front originating from the
Bering and western Aleutians is forecast to move quickly across
interior sections of the mainland Sunday. Moisture advection
ahead of the front will support patchy areas of moderate to
locally heavy snow across the Seward Peninsula, the southern part
of the Brooks Range, and eastward
toward the Fairbanks area and the central Interior. Some of this
snow will likely be accompanied by strong winds, leading to
blowing snow
and localized blizzard conditions, particularly in mountain
passes. Another round of accumulating snow will be possible by
next Tuesday depending on the track of the next storm system
entering the Bering. In the temperature department, frigid
conditions are expected for eastern and northern portions of the
mainland this weekend, with a moderating trend commencing by late
Sunday and a return to above normal readings by the early to
middle part of next week.
Hamrick
Hazards:
- Heavy snow across portions of mainland Alaska, Sun, Dec 26.
- High winds across portions of mainland Alaska, Fri, Dec 24.
- Much below normal temperatures across portions of the Alaska
Panhandle, Fri-Tue, Dec 24-Dec 28.
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