Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
658 PM EDT Sun Oct 17 2021
Valid 12Z Thu Oct 21 2021 - 12Z Mon Oct 25 2021
...Stormy pattern continues into next weekend from the Aleutians
to Southern and Southeast Alaska...
... Guidance and Predictability Assessment...
Upper level low pressure should remain parked over the Gulf of
Alaska through the period as multiple shortwaves dropping through
the Aleutians and into the Gulf reinforce the upper pattern. The
guidance shows good agreement on the large scale pattern through
most of the period but continues to struggle with the details,
especially later in the period. Big uncertainties across the board
loom, especially regarding triple point low redevelopments in the
Gulf, shortwaves crossing south of the Aleutians, and another
system making its way into the Bering Sea by the end of the
period. WPC relied on a majority blend of the deterministic
guidance for the first half of the period, but quickly
transitioned to mostly ensemble means by the end to help smooth
out the smaller scale, harder to resolve details. Some preference
was given towards the ECMWF and the CMC over the GFS given better
consistency with the ensemble means. This approach maintained
reasonable continuity from yesterdays forecast, as well as with
downstream across the CONUS.
...Pattern Overview and Weather/Hazard Highlights...
The period starts Thursday with a deep surface low lifting
northward into the Gulf and slowly weakening. This should keep
unsettled wet weather in the forecast from the southern coast to
the Panhandle. Most places should see just scattered light to
moderate precipitation, though locally heavy precipitation is
likely in some spots, with snow in the higher elevations.
Meanwhile, another system should cross the Aleutians on Thursday
with widespread precipitation and gusty winds likely to accompany.
As the system slides east, a couple of triple point developments
should act to reinforce mean low pressure across the Gulf through
next weekend. This should maintain generally soggy conditions from
southeast Alaska to the Panhandle, with conditions finally
starting to improve by early next week as the cold front pushes
into western North America.
Temperatures from the Aleutians to the Panhandle should be mostly
below normal through the period as surface low pressure and upper
level troughing becomes established over the region. Into the
interior and northern Alaska, periods of upper level ridging
should keep daytime highs as much as 10 to 20 degrees above normal
into next weekend.
Santorelli
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