Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
459 PM EST Mon Dec 06 2021
Valid 12Z Fri Dec 10 2021 - 12Z Tue Dec 14 2021
...Another Major Storm for Alaska...
...Overview and Guidance Evaluation/Preferences and Weather/Hazard
Highlights...
Strong upper energies supporting a deep Bering Sea storm Thursday
are slated to transfer robustly downstream over Southwest Alaska
and the Alaskan Peninsula/Kodiak Island to re-develop a powerhouse
low near the Kenai Peninsula by Friday whose large circulation
will affect much of the state. Subsequent system track over the
eastern Gulf of Alaska next weekend into early next week will act
to spread the threat of high winds and Gulf waves along with heavy
coastal rains and terrain enhanced heavy snows from south-central
Alaska to the southeast Panhandle. Expect much below normal
temperatures will settle over the Aleutians through southwest and
southern portions of the state in the wake of system passage. All
these threats are detailed in the latest WPC Day 3-7 Hazards
Outlook product listed and linked below.
12 UTC GFS/ECMWF/UKMET/Canadian solutions seem well clustered
through days 4/5 (Fri/Sat), bolstering forecast confidence. The
GFS/ECMWF remain best clustered and in line with ensembles and WPC
continuity Days 6/Sun before forecast spread become more daunting
day 7/8. Prefer by then a composite of still reasonably compatible
GEFS/ECMWF ensemble means in a pattern with rapidly decreasing
predictability. There is a slowly growing guidance signal to
support additional Bering Sea storm genesis into these longer time
frames, but with an uncertain downstream track and re-development
toward Alaska. The 12 UTC GFS seems a distinct outlier more
directed to mainland Alaska compared to a better supported track
suppression to the Gulf of Alaska, albeit with varied 12 UTC
ECMWF/Canadian and ensemble member details.
Schichtel
Hazards:
- Heavy precipitation across portions of mainland Alaska, Thu, Dec
9.
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Fri, Dec 10.
- High winds across portions of mainland Alaska and the Aleutians,
Thu-Sat, Dec 9-Dec 11.
- Much below normal temperatures for parts of mainland Alaska and
the Aleutians, Sat-Mon, Dec 11-Dec 13.
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