Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
639 PM EDT Fri Aug 20 2021
Valid 12Z Tue Aug 24 2021 - 12Z Sat Aug 28 2021
...An Active Weather Regime for Alaska..
...Guidance/Predictability Evaluation...
12 UTC GFS/ECMWF solutions seem reasonably well clustered days 3-7
across much of Alaska and adjoining waters, albeit with the ECMWF
more amplified with time into the Interior within an energetic and
unsettled Arctic stream. Underneath in an also active mid-upper
latitude stream from the Bering Sea and northern Pacific into the
Gulf of Alaska, a blend of the more amplified 12 UTC GFS/ECMWF
seems to better fit upstream flow ridge amplitude than the
somewhat more progressive solutions from the 12 UTC
Canadian/UKMET, GEFS/ECMWF ensemble means and WPC continuity.
Accordingly and considering overall forecast spread, the WPC
Alaskan medium range product suite was primarily derived from a
blend of the GFS/ECMWF, but also smaller inputs of the GEFS/ECMWF
ensemble means to address lingering uncertainties.
...Pattern Overview and Weather/Threats Highlights...
An amplified flow pattern next week should maintain wet and
unsettled conditions across much of Alaska.
Southerly fetch ahead of a series of energetic systems set to work
across the Gulf next week will direct significant moisture into
southern Alaska fueling moderate to heavy rainfall from parts of
the southern Coast to the Panhandle. Higher elevations will also
see measurable snowfall.
Meanwhile, potent shortwaves interacting with a persistent Arctic
frontal boundary will allow organized precipitation periodically
across northern and Interior Alaska. In particular, an organized
low pressure system reaching northwest Alaska Thursday will bring
increased chances for enhanced rainfall inland into later next
week. The pattern supports below normal maximum temperatures for
much of Alaska.
Schichtel
Hazards:
- Heavy rain across portions of the Alaska Panhandle and mainland
Alaska, Tue-Wed, Aug 24-Aug 25.
- Heavy rain across portions of mainland Alaska, Mon, Aug 23.
- High significant wave heights for coastal portions of mainland
Alaska, Thu, Aug 26.
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