Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
642 PM EDT Thu Aug 12 2021
Valid 12Z Mon Aug 16 2021 - 12Z Fri Aug 20 2021
...Pattern Overview...
A closed upper low will linger in the Arctic/Beaufort through much
of next week with systems moving eastward underneath its
circulation across northern areas. Additional troughing will
reload near the Aleutians into the Gulf to the north of building
upper ridging in the mid-latitudes. This keeps a quasi-zonal flow
across much of the mainland into the Panhandle with several
systems and rainfall episodes.
...Guidance/Predictability Evaluation...
The 12 UTC ECMWF/GEFS/NAEFS ensemble means remained in reasonable
agreement overall with some expected timing/amplitude differences
next week over the Bering and near the Aleutians as a couple less
certain systems enter the region. Overall, a blended guidance
solution was preferred with the means along with the 12Z ECMWF
which paired best with the ensembles and WPC continuity.
...Weather/Threats Highlights...
Over northwestern areas, deep upper low in the Arctic will allow a
northern stream system out of Russia to push eastward
underneath/around its circulation. This will bring in an expanding
area of precipitation to the northwestern corner of the state and
across the Brooks Range early next week as the boundary slowly
sinks southward and then eastward just ahead of the upper trough
and with approach of a compact Bering Sea low.
Lead systems this weekend containing the remnant moisture of
ex-Tropical Storms Lupit and Mirinae, will tend to lift
northeastward toward the central/eastern Aleutians and
AKPen/Northern Gulf of Alaska into early next week, bringing in
some enhanced rainfall to the region. Long fetch moisture pulled
northeastward may also favor heavy precipitation downstream
through midweek into southern/southeast Alaska as additionally
enhanced by terrain.
Temperatures will generally be below normal across most of the
state, focused on northern areas under the trough. Some slow
moderation is possible later next week but the continued troughing
will likely result in only small changes to the pattern.
Schichtel
Hazards:
- Heavy rain across portions of mainland Alaska, Mon, Aug 16.
- Heavy rain across portions of the Alaska Panhandle and mainland
Alaska, Tue-Wed, Aug 17-Aug 18.
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