Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
434 PM EST Tue Dec 01 2020
Valid 12Z Sat Dec 05 2020 - 12Z Wed Dec 09 2020
...Significant Gulf of Alaska storms offer a weekend to early next
week heavy precipitation and high wind threat for southern to
southeast Alaska....
...Guidance and Uncertainty Assessment...
Forecast spread remains less then stellar, so system timing and
placement details remain more suspect than usual through medium
range time scales. Accordingly, the WPC Alaskan medium range
product suite was primarily derived from the mainly compatible 12
UTC GEFS/ECMWF ensemble means and the 19 UTC National Blend of
Models. The overall larger scale pattern evolution in guidance
offers better predictability, so manually adjusted offshore
surface low systems deeper as consistent with favorable support
aloft and deepening model system trends. This solution was
collaborated with local Alaskan offices and maintains good WPC
continuity.
...Weather/Hazards Highlights...
Expect an overall more benign weather pattern to settle into much
of the North Slope and the Interior heading this weekend.
Underneath, a lead Pacific system lifting up through the eastern
Gulf of Alaska Saturday offers less than ideal model forecast
spread, but does show potential to focus heavy precipitation and
high winds from a stormy Gulf into southern/southeast Alaska. A
subsequent and much deeper/larger low with amplified upper
trough/low support has a growing guidance threat signal for major
maritime disruption and heavy precipitation/high winds across the
Gulf and onshore back into southern and southeast Alaska later
weekend into early next week. Additional low energies upstream
with more uncertain development potential are then slated to work
from the Pacific toward the Aleutians and the Gulf early-mid next
week in continued unsettled flow.
Schichtel
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Sat-Mon, Dec 5-Dec 7.
- Heavy precipitation across portions of the Alaska Panhandle,
Fri-Mon, Dec 4-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