Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
424 PM EDT Sat Jul 18 2020
Valid 12Z Wed Jul 22 2020 - 12Z Sun Jul 26 2020
The forecast for the latter portion of next week is for persistent
mid-level height anomalies across mainland Alaska associated with
an arctic upper low and trough situated north of the state, with
positive height anomalies over the Aleutians turning negative
with time. The 12z GEFS shows a west drift of the trough axis with
time, which next weekend opens up the possibility of heights
rising and temperatures moderating back towards 30 year normal
over the AK panhandle/southeast AK.
The primary storm system in the medium range is expected to form
over the western Bering Sea and is expected to drift slowly
towards the east in the mid to latter portions of next week. The
00z ECMWF was offset from the majority cluster and the new 12z run
has come into better agreement with both the 12z GFS and its own
00z ECMWF Ensemble Mean.
With increased clustering among solutions, a blend of the 12z
ECMWF/00z ECMWF Ensemble Mean, 12z GEFS Mean, and 12z GFS was
used.
The CMC was more progressive with the system and also for heights
to lower in the Gulf of AK/Kodiak/AK peninsula days 7-8, so the
Canadian was not included in the blend given the majority of
solutions are high amplitude and slow.
The ECMWF/UKMET/Canadian cluster better with the 00z ECMWF
Ensemble Mean with low pressure in the Arctic Ocean, so the 12z
GFS was given less weight there.
Finally, on days 7-8, the GFS produces a triple point low south of
the Aleutians and moves the low towards the Gulf of AK Day 8.
Given the GFS was stronger than other solutions, the GFS was given
less weight, with the use of the 12z GEFS Mean to mitigate
uncertainties, along with the 00z ECMWF Mean and operational 12z
ECMWF.
Petersen
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards 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