Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
604 PM EDT Fri Aug 13 2021
Valid 12Z Tue Aug 17 2021 - 12Z Sat Aug 21 2021
...Overview...
It remains generally the case that a closed upper low will linger
in the Arctic Ocean 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 enhanced rainfall episodes.
...Guidance/Predictability Evaluation...
12 UTC GFS/ECMWF solutions now seem better clustered, fit well
with WPC continuity and overall sit near the middle of the full
envelope of model and ensemble solutions days 4-6 (Tue-Thu). Favor
bringing into the composite increasing amounts of compatible but
less detailed GEFS/NAEFS/ECMWF ensemble means into days 7/8 to
address growing forecast spread as predictability lowers from
above to near normal.
...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-Fri, Aug 17-Aug 20.
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