Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
636 PM EST Wed Dec 01 2021
Valid 12Z Sun Dec 05 2021 - 12Z Thu Dec 09 2021
...Large storm system to bring heavy snow and gusty winds to parts
of western Alaska Sunday-Monday...
...Overview and Guidance Evaluation/Preferences...
Parts of the Alaska region should become increasingly active
through this weekend and into early next week as amplified
troughing brings a deep cyclone across the Bering Sea and into
western Alaska by next Monday. The system should weaken as it
tracks through the Mainland though additional triple point
development along the Gulf Coast should send a cold front towards
the Panhandle region mid week. Meanwhile, an additional shortwave
tracking towards the Aleutians next Wednesday into Thursday may
send another deep low pressure system into the southern/western
Bering Sea.
In general, the guidance shows relatively good agreement through
the first couple days of the period on the overall synoptic
pattern, with the exception of the 12z CMC which was noticeably
slower/southwest of the better consensus for the Bering
Sea/western Alaskan low. By day 6/Tuesday, more of the typical
timing and detail differences begins to arise, especially
surrounding the next low towards the Aleutians and possibly into
the Bering Sea. The GFS/CMC and ensemble means support this low
lifting into the Bering Sea, while the 12z ECMWF keeps the low
well south of the Aleutians.
The WPC forecast progs used a deterministic model blend (minus the
12z CMC) for days 4-5, gradually increasing weighting of the
ensemble means thereafter to help smooth out the smaller scale
uncertainties which will need more time to resolve. This approach
maintains good continuity with yesterday's WPC forecasts as well.
...Weather/Hazard Highlights...
The Bering Sea cyclone will usher in a much more active weather
pattern across Alaska consisting of windy and snow conditions.
Much of western Alaska will experience snow Sunday into Monday,
with the greatest threat across parts of the Seward Peninsula and
southwestern Alaska. Current guidance suggests some locations
could see upwards of a foot of snow, along with a period of gusty
winds as the low moves inland on Monday. Increasingly wet weather
will also move into parts of the Southern Coast and southeast
Alaska Monday into Tuesday again with a threat for locally heavy
snows, especially across the favorable terrain. The cold front
propagating through the Gulf should bring increased rain chances
to the Panhandle mid week next week with rain again threatening
the Aleutians as well with the next low pressure system into the
region.
After a period of much below normal temperatures, conditions
should finally begin to moderate from west to east by the start of
the extended period on Sunday as the Bering Sea low brings milder
air in from the south. By next Monday, much of interior and
northern Alaska should see temperatures near or above normal, with
the greatest anomalies likely across parts of western Alaska and
the North Slope region.
Santorelli
Hazards:
- Heavy snow across portions of southwestern Alaska, Mon, Dec 6.
- High winds across portions of Seward Peninsula in Alaska, Sun,
Dec 5.
- Much below normal temperatures across portions of central and
eastern Alaska, Sat, 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