Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
559 PM EDT Sun Jul 19 2020
Valid 12Z Thu Jul 23 2020 - 12Z Mon Jul 27 2020
The forecast for the latter portion of this week through next
weekend is for persistent negative mid-level height anomalies
across mainland Alaska associated with an arctic upper low and
trough situated north of the state. This trough and sfc frontal
systems lead to cooler than normal temperatures and a few showery
periods, currently centered on Thu and Sat.
The ECMWF Ensemble Mean 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 normals
over the AK panhandle.
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 this week. The
models show typical run to run differences
and model to model differences. Without unanimity and general
clustering of solutions, a blend of the 12z ECMWF/00z ECMWF/00z
ECMWF Ensemble Mean, 12z GFS, and 12z UKMET was used. The 12z
Canadian global was more progressive with the system and also for
heights to lower in the Gulf of AK/Kodiak/AK peninsula days 6-7,
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 6-8, more models produce a couple of waves of low
pressure south of the Aleutians and move the lows across the Gulf
of AK.
A blend of the 06-12z GFS and 00-12z ECMWF was used to mitigate
timing differences. Shower coverage and intensity should increase
next Sunday and Monday July 27
in the AK panhandle if these solutions are correct.
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