Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
632 PM EDT Mon Aug 17 2020
Valid 12Z Fri Aug 21 2020 - 12Z Tue Aug 25 2020
...Guidance Evaluation and Preferences...
Models/ensembles continued to relatively good consensus from
recent days through the first part of the extended period (days
4-5), but showed more degradation compared to recent days later in
the forecast period. A blend of the 12Z GFS/ECMWF was used during
days 4-5 (Thu-Fri), with more weight on the ECMWF relative to the
GFS. In the large scale sense, the solutions were not
fundamentally different though the ECMWF favored closely with the
ECENS/GEFS means, especially by days 6-8. While deterministic
solutions showed greater differences, a blend of ensemble means
likely represents the best consensus approach here by later in the
forecast period, so higher weights of the ECENS and GEFS was
incorporated. Thus, starting on day 6 (Sat) and continuing through
day 8 (Mon), a gradual shift toward heavier use of ECENS/GEFS
ensemble means was shown.
...Weather Highlights/Threats...
For the forecast period, one low pressure system is forecast to
cross the southern areas of the Gulf of Alaska through later this
week, bringing widespread precipitation across the Panhandle. Then
some periods of upper ridging across the Bering Sea and western
Alaska will lead to drier periods, while wetter conditions prevail
over the Panhandle and Southeast Alaska. From the mid to late
forecast periods, another strong low pressure system to cross the
Bering Sea, moving onshore over western Alaska into the early
portions of the new week. Temperature wise, readings will favor
above normal initially then begin to trend toward normal late in
the period.
Ryan/Taylor
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