Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
622 PM EDT Thu Aug 5 2021
Valid 12Z Mon Aug 9 2021 - 12Z Fri Aug 13 2021
***Heavy rainfall expected for portions of southern Alaska next
week***
...Overview and Guidance/Predictability Evaluation...
A broad upper level trough is expected to be in place across much
of the state and extending across much of the Bering Sea and the
Aleutians. An upper level ridge axis situated over British
Columbia will tend to limit the eastward progress of the trough,
resulting in rather unsettled weather across much of the southern
third of the state, particularly from the Kenai Peninsula to the
southeast Panhandle region. Meanwhile, a closed low over the
Arctic will likely send a cold front southward across the North
Slope and Brooks Range.
On the synoptic scale, the deterministic guidance is in relatively
good agreement, but the 12Z UKMET begins to deviate across the
Gulf with a more progressive solution with a shortwave emanating
from the main upper trough axis. The 12Z CMC has come into better
agreement regarding the placement of the arctic low and is similar
in latitudinal placement with the ECMWF, while displaced from the
more northern GFS solution. By the end of the forecast period,
the CMC becomes a bit more amplified with the trough over the
northern Gulf, but still within the realm of possibility. The WPC
fronts/pressures forecast was primarily derived from a 12Z
GFS/ECMWF/CMC blend, along with some previous WPC continuity,
through Wednesday, and then more of the EC and GEFS means for the
end of next week.
...Weather/Threats Highlights...
The upper level troughing over the state will tend to keep
temperatures below early August averages across most of the state
next week. These anomalies will likely be even greater for the
Brooks Range and points northward with the arctic front moving
through in response to the closed low north of the Arctic Coast.
In terms of precipitation, multiple rounds of moderate to heavy
rain are expected from the Alaska Peninsula to the southeast
panhandle region, with some locations potentially getting 2 to 4
inches of rainfall across topographically favored areas. This may
lead to some instances of flooding and enhanced run-off. There
may even be some snow showers for the northern third of the state,
especially for the Brooks Range.
Hamrick
Hazards:
- Heavy rain across portions of the Alaska Panhandle and
south-central mainland Alaska, Sun-Thu, Aug 8-Aug 12.
- Heavy rain across portions of the Alaska Panhandle, Mon-Wed, Aug
9-Aug 11.
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