Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
606 PM EST Mon Dec 27 2021
Valid 12Z Fri Dec 31 2021 - 12Z Tue Jan 04 2022
...Overview...
A deepening low pressure will track from the eastern Bering Sea
across the southern mainland into the Gulf of Alaska this weekend,
bringing widespread snow to southern mainland and the southeastern
areas. In its wake, a pronounced blocky pattern is forecast to
develop which should allow for much below normal temperatures to
dig southward across the southern, eastern, and southeastern
areas.
...Overview and Guidance Evaluation...
Today's 12Z model guidance suite showed fairly good agreement and
predictability throughout the period with the expected evolution
toward a more amplified pattern. At the start of the period
/12-31/, an area of low pressure over the eastern Bering shows
good agreement between the latest deterministic model guidance and
that low is forecast to track through southern Alaska into the
Gulf of Alaska. As it does so, the upper level pattern is forecast
to become more blocky. An eastern Gulf upper trough deepens and
the whole system slowly occludes through day 6. This scenario had
good agreement such that a near equal multi-model blend was
incorporated for days 4-6. Beyond that time frame, the signal for
a pronounced and highly amplified pattern is increasing with
impressive height anomalies. This setup favors strong/cold high
pressure over the eastern mainland or northwest Canada with some
of the deterministic guidance hinting at 1050+ mb high early next
week. The days 6-7 blend incorporated more of the ECENS and GEFS
means to account for the increasing model spread in that time
frame.
...Weather/Hazard Highlights...
A surface low will track through the Bering Sea, bringing
widespread light to moderate precipitation inland across southwest
to south-central Alaska while a deeper fetch of moisture will
support heavy snow for much of the Panhandle on Friday into
Saturday. Amounts of up to or exceeding a foot are possible,
though right along the coast, totals may be lighter as
precipitation mixes with rain. Behind this feature, a strong
Arctic airmass will pour southward bringing much below normal
temperatures to eastern sections of Interior Alaska, much of
southwestern and south-central Alaska and possibly into the
Panhandle for early next week.
Taylor
Hazards for Alaska for Dec 31 - Jan 4:
- Heavy snow across portions of the Alaska Panhandle and mainland
Alaska, Fri-Sat, Dec 31-Jan 1.
- High winds across portions of the Alaska Panhandle and mainland
Alaska, Sat-Sun, Jan 1-Jan 2.
- High winds across portions of the Aleutians, Thu, Dec 30.
- Much below normal temperatures across portions of the Alaska
Panhandle and mainland Alaska, Sun-Mon, Jan 2-Jan 3.
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