Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
539 PM EST Mon Nov 16 2020
Valid 12Z Fri Nov 20 2020 - 12Z Tue Nov 24 2020
...Deep late week lows to threaten Southwest/Southern Alaska...
...Guidance/Predictability Assessment...
The WPC Alaskan medium range product suite was primarily derived
from a composite blend of the reasonably compatible 12 UTC
GFS/ECMWF, the 12 UTC GEFS mean and the 19 UTC National Blend of
Models days 4-6 (Fri-Sun) in a pattern with average to above
average system predictability. Used a mass field solution close to
the 12 UTC GEFS mean days 7-8 amid quickly growing forecast
uncertainty, but manually adjusted offshore lows deeper consistent
with favorable upper support and model trends. The 00 UTC ECMWF
was an unusual outlier days 7/8, but the 12 UTC run has trended
toward the 12 UTC GEFS mean in a pattern with below normal
predictability.
...Weather/Threats Highlights...
There remains a strong guidance signal supporting amplified upper
trough/closed low developments into the Bering Sea and Aleutians
into late week, with additional reinforcements into early next
week. These will offer several significant threats for deep
offshore storms to focus enhanced winds/waves and precipitation
across the region. Downstream energy transfer later week through
early next week will also increasingly threaten southwest Alaska,
southern Alaska, then southeast Alaska as ample upper
trough/deepened storm energies work more in earnest into and
across the Gulf of Alaska.
Schichtel
Hazards:
- Heavy precipitation across portions of mainland Alaska and the
Aleutians, Fri, Nov 20.
- High winds across portions of mainland Alaska and the Aleutians,
Fri, Nov 20.
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