Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
640 PM EST Tue Nov 30 2021
Valid 12Z Sat Dec 04 2021 - 12Z Wed Dec 08 2021
...Well below normal temperatures over southwestern Alaska will
give way to snowy and windy conditions late this week and into
early next week...
...Guidance Evaluation/Preferences...
The Alaska region should become increasingly active through this
weekend and into early next week as amplified troughing sends a
deep cyclone across the northern Bering and into western Alaska by
next Monday. This system should weaken as it moves through the
interior with additional triple point low development possible
along the Gulf Coast next Tuesday-Wednesday. The guidance
continues to show fairly good agreement on the large scale with
mainly the typical timing and detail differences in various
systems. The greatest differences seem to surround the amplified
trough/deep surface low into the Bering and western Mainland this
weekend. Although guidance is reasonably in agreement in the upper
pattern, this translates to some more significant differences at
the surface among the deterministic solutions. Both the 12z ECMWF
and CMC suggest the surface low may lift farther northward towards
the North Slope region, while the GFS (and the ensemble means)
show the low moving more eastward into the Mainland.
The WPC forecast progs used a general model blend between the
deterministic models for days 4-5, gradually increasing weighting
of the ensemble means thereafter to help smooth out the detail
uncertainties which will need more time to resolve. This approach
maintains good continuity with yesterday's WPC forecasts as well.
...Weather/Hazard Highlights...
Alaska should initially start very chilly with much below normal
temperatures on Saturday. Daytime highs could average 20-30+
degrees below average across much of the Southwest and into
interior and eastern Alaska. By Sunday, temperatures should begin
to moderate as a low pressure system into the Bering Sea brings
milder air from the south, along with periods of snowy and windy
weather. Snow chances across western and southwestern Alaska
should increase on Saturday, with the greatest threat for snow
Sunday into Monday across the interior southwestern Alaska and
points farther north, particularly along favored terrain enhanced
regions. Guidance suggests right now moderate snowfall amounts of
generally around a foot (or less) is expected, though there is
potential some locations could see more. Snow should propagate
into parts of southeast Alaska too, though the heaviest amounts
should be confined to mountainous areas. This system should also
bring rain and wind to the Aleutians and into the Peninsula region
this weekend, with precipitation chances increasing again early
next week across the southern coast to Panhandle as the cold front
moves through the Gulf.
Santorelli
Hazards:
- Much below normal temperatures across portions of southwestern
Alaska, Fri, Dec 3.
- Much below normal temperatures across portions of southwestern
and interior Alaska, Fri-Sat, Dec 3-Dec 4.
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