Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
515 PM EST Wed Dec 02 2020
Valid 12Z Sun Dec 06 2020 - 12Z Thu Dec 10 2020
...Major Gulf of Alaska Storm offers a heavy precipitation and
high wind threat for southern to southeast Alaska this weekend and
early next week....
...Guidance and Uncertainty Assessment...
Guidance variance has decreased overall, bolstering forecast
confidence in the formation of a major Gulf of Alaska storm this
weekend into early next week. The 12 UTC GFS and ECMWF are well
clustered models that reasonably continue to trend increasingly
deep with the main storm considering favorable upper support to
provide a seemingly good forecast starting point Sun/Mon into Tue.
Forecast spread increases enough through next midweek to favor a
blend of still reasonably compatible 12 UTC GEFS/ECMWF ensemble
means. The WPC Alaskan medium range product suite was accordingly
derived along with the 19 UTC National Blend of Models. This
solution maintains good WPC continuity.
...Weather/Hazards Highlights...
A deep and large storm with amplified upper trough/low support has
a growing guidance threat signal for major multi-day maritime
disruption and heavy precipitation/high winds across the Gulf of
Alaska and onshore into southern and southeast Alaska this weekend
and early next week. Farther inland to the north, a generally
benign weather pattern is expected for much of the North Slope and
the Interior except for more modest early next week spillover
moisture/snows into the Interior as the aforementioned deep low
shifts northward over the Gulf toward southern Alaska. Additional
low energies upstream with less certain development potential to
monitor are subsequently slated from the northern Pacific toward
the Aleutians and vicinity next midweek.
Schichtel
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Sat-Mon, Dec 5-Dec 7.
- High winds across portions of the Alaska Panhandle and mainland
Alaska, Sat-Sun, Dec 5-Dec 6.
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards 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