Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
717 PM EDT Mon Aug 30 2021
Valid 12Z Fri Sep 03 2021 - 12Z Tue Sep 07 2021
...Pattern Overview and Model Guidance...
Upper troughing over the Bering and southwestern areas will slip
into the Gulf this weekend via two separate entities. Any ridging
over eastern areas of the mainland will weaken into Canada after
Friday as the flow becomes southwesterly aloft. Farther upstream
over the East Siberian Sea, another upper low will slowly move
toward the Bering Strait but with most of its focus over
northeastern Russia. The models agreed overall on the evolution
but the 12Z GFS strayed farthest from the generally good ECMWF-led
agreement (with the Canadian mostly, and to a smaller degree the
UKMET) and it was not used. In fact, differences appeared as soon
as F24 south of the Aleutians which was unusual for such a short
lead time. Other areas over the domain exhibited expected spread
that increased with time, but the GFS remained just outside the
ensemble agreement that included its own GEFS mean. Utilized the
12Z ECMWF most for a deterministic weight with an increased
ensemble mean weighting (ECMWF + GEFS) by next week (Sun-Tue).
...Sensible Weather...
Exiting system later this week will take its heavy rain threat
into Canada with some lingering areas of at least modest rain near
the area of low pressure near Haida Gwaii Friday and also over the
eastern portion of the Kenai Peninsula. Subsequent system should
bring in another round of light to modest rains for the Panhandle
late Sat into Sun. For the rest of the state, troughiness will
support a rather unsettled period with widespread light showers
and snow at higher elevations as temperatures generally cool with
time. Front moving into northwestern areas will support more
organized rain/snow to the Seward Peninsula into the Brooks Range
but likely still light to modest amounts. Additional enhancement
is possible farther east as the front advances toward the Yukon.
Temperatures will start the period within 5-10 degrees of normal
(above normal over much of the Interior and below normal along
coastal areas) with a trend toward cooler than normal temperatures
from northwest to southeast next week. Temperatures in the 50s/60s
will generally fall to the 40s/50s as the cold front moves through.
Fracasso
Hazards:
- Heavy rain across the eastern portion of the Kenai Peninsula,
Thu-Fri, Sep 2-Sep 3.
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