Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
702 PM EDT Tue Aug 10 2021
Valid 12Z Sat Aug 14 2021 - 12Z Wed Aug 18 2021
...Heavy rain southeastern Alaska Saturday...
...Overview...
Upper pattern remains rather stagnant as features move through the
flow, maintaining troughing over the Bering Sea in between
upstream and downstream ridging. This will keep an active pattern
over the high latitudes into next week with both the northern and
southern stream affecting the 49th state. System exiting through
the Panhandle Saturday will bring its significant heavy
precipitation threat out of the area with a drier few days to
follow. The Aleutians and northwestern areas will see a couple
systems move through or near the areas with abundant clouds and
numerous showers.
...Guidance/Predictability Evaluation...
The ensembles remained in good agreement overall with some
expected timing/amplitude differences next week over the Bering
and near the Aleutians as a couple more systems enter the picture.
Overall, a blended solution was preferred. This included the 12Z
ECMWF which paired best with the ensembles, followed by the 12Z
GFS and part of the Canadian. The UKMET was again farthest from
the consensus. The systems south of the Aleutians, containing the
remnant moisture of ex-Tropical Storms Lupit and Mirinae, will
tend to lift northeastward toward the central/eastern Aleutians
and AKPen next week, bringing in some rainfall to the region.
Timing differed in the guidance but was within the expected spread
for this time range. Again, a middle ground solution showed little
change from the forecast 24 hrs ago.
...Weather/Threats Highlights...
Some locally heavy rainfall will be possible early Saturday over
the Panhandle as the front clears through the area, followed by
some showers and then clearing. To the north, deep upper low in
the Arctic will allow another 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 next week as the
boundary slowly sinks southward and then eastward just ahead of
the upper trough.
Temperatures will generally be below normal across most of the
state, focused on northern areas. Some slow moderation is possible
next week but the continued troughing will likely result in only
small changes to the pattern, perhaps nearing or above normal
temperature across the Aleutians by next Wednesday.
Fracasso
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
Hazards:
- Heavy rain across portions of the Alaska Panhandle and mainland
Alaska, Fri, Aug 13.
- Heavy rain across portions of mainland Alaska, Sun-Mon, Aug
15-Aug 16.
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