Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
654 PM EDT Sun May 23 2021
Valid 12Z Thu May 27 2021 - 12Z Mon May 31 2021
...Overview and model guidance...
The overall pattern across Alaska for the medium range will
feature a large scale upper level low that will slowly move over
or just south of the Aleutians the first half of the period,
getting blocked and meandering near the eastern Aleutians by next
weekend as upper level ridging amplifies over the mainland.
Troughing may try to briefly move through northern/northeast
Alaska late this week before shifting into northwest Canada by the
end of the period.
Guidance continues to show good agreement on the large scale
pattern, but increasing uncertainty in the details towards the end
of the period. The 12z ECMWF shifted its upper low position to
closer match the GFS so the blend for the first half of the period
favored a general model compromise. After day 5, the CMC seemed
too eager to bring a closed low across northern Alaska and into
the western Bering Sea where it then becomes the main upper low as
the Aleutians low weakens. The ECMWF also supports energy drifting
westward across Alaska, but weakens it late in the period keeping
emphasis on the southern low. The ensembles also support
maintaining a decent low across the Aleutians through the entire
period, so after day 5 the CMC was excluded from the blend. The
forecast for today favored a majority ensemble mean blend by day
8, with some inclusion of the GFS/ECMWF for added
detail/definition. Overall, this approach seems to fit well with
previous WPC continuity.
...Weather/Threats Highlights...
The low pressure center and associated frontal system into the
Aleutians should bring a period of unsettled weather to areas from
the Aleutians to the southern mainland Coast. Fronts and embedded
waves may provide some localized enhancement of precipitation and
winds at times, but nothing seems particularly heavy or hazardous
at this time. The best signal for highest totals during the
five-day period exists from the eastern Aleutians to the Kenai
Peninsula/Prince William Sound, with totals during that period of
an inch or more. For temperatures, the Panhandle and southern
coastal regions should remain at least modestly below normal
through the entire period. North Slope to northeast Alaska may be
much below normal to begin the period, but should moderate back
towards normal (or slightly below) by the weekend. Much of western
Alaska will remain near or above normal as upper level ridging
holds in place aloft over these areas.
Santorelli
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