Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
651 PM EDT Fri Sep 04 2020
Valid 12Z Tue Sep 08 2020 - 12Z Sat Sep 12 2020
...Stormy conditions should gradually subside by the middle of
next week; extratropical Haishen may reach the western Aleutians
by next weekend...
Windy and rainy conditions associated with an occluded cyclone
should still be the main story early next week especially for
western Alaska. Conditions will slowly improve by the middle of
next week as the cyclone weakens into a trough along the Brooks
Range. Considerable clouds and scattered areas of rain will
linger over mainland Alaska into the latter part of next week with
cool afternoons and milder than normal nights. The best chance of
heavy rain will be on the southern periphery of the state, from
the Alaska Peninsula on Labor Day, shifting east toward the
northern Panhandle by Tuesday into Wednesday.
Toward the end of next week, there was a significant shift in the
forecasts led by the 00Z EC mean from the Aleutians westward. The
GEFS and Canadian means have not responded to this change yet but
the 12Z GFS and 12Z ECMWF agree fairly well to abandon the idea of
having a cyclone approaching the central Aleutians from the
southwest by next weekend. The reason for this pattern shift
appears to be due to more energy is given to the extratropical
amplification of Super Typhoon Haishen currently south of Japan
which will then absorb the low that is forecast to drift into the
western Aleutians by the middle of next week. This pattern shift
does not appear to impact the forecast all that much for mainland
Alaska, however.
The WPC Day 4-8 Alaskan prognostic charts were based on a blend of
the 00Z EC mean, 12Z ECMWF, 12Z GFS and the 12Z GEFS with more
emphasis toward an even blend of the 12Z GFS and ECMWF for Days 7
and 8.
Kong
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
Hazards:
- Heavy rain across portions of mainland Alaska, Mon, Sep 7.
- Heavy rain across portions of the Alaska Panhandle and mainland
Alaska, Tue-Wed, Sep 8-Sep 9.
- High winds across portions of mainland Alaska, Mon-Tue, Sep
7-Sep 8.
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