Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
700 PM EDT Sat May 22 2021
Valid 12Z Wed May 26 2021 - 12Z Sun May 30 2021
...Overview and model guidance...
The overall weather pattern will generally feature a large scale
upper low that will slowly move from the southern Bering Sea to
the eastern Aleutians region during the medium range period.
Multiple shortwave perturbations and surface lows are expected to
pivot around this main upper low and produce episodes of rainfall
for southern Alaska. Meanwhile, an upper level ridge axis should
extend from southeast to northwest across mainland Alaska, and an
Arctic trough should pass over northeast Alaska and northwest
Canada.
In terms of model choices, the WPC medium range forecast started
with a blend of the 12Z ECMWF/GFS/UKMET for the Wednesday-Thursday
time period. Similar to yesterday, the CMC differed more from the
ensemble means along with greater timing differences, so it was
not favored for this forecast cycle. Beyond that time, the
forecast trended to include more of both the ECENS and GEFS mean
to account for timing differences with individual shortwaves and
amplitude. Some previous WPC continuity was also included.
...Weather/Threats Highlights...
The initial low pressure center and associated frontal system over
the Bering Sea and central Aleutians, as well as one or more
trailing systems that may merge into the overall mean low, should
bring periods of unsettled weather to areas from the Aleutians
through at least the Alaska Peninsula, and then portions of the
mainland southern coast. Fronts and embedded waves may provide
localized enhancement of precipitation and winds at times. The
best signal for highest totals during the five-day period exists
from the eastern Aleutians to the Kenai Peninsula, with some areas
likely to receive an inch or more of rainfall. In terms of
temperatures, the Panhandle and portions of the southern mainland
as well as parts of the North Slope will tend to see slightly
below normal high temperatures during the period. Other locations
will likely experience near to above normal highs with the upper
ridge in place.
Hamrick
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