Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
713 PM EDT Mon Oct 18 2021
Valid 12Z Fri Oct 22 2021 - 12Z Tue Oct 26 2021
...Pattern overview and Guidance and Predictability Assessment...
A low pressure system in Bristol Bay to start the period on Friday
should begin to weaken as it crosses the Alaska Peninsula and
redevelops its triple point well to the southeast. This new low
should lift north and east towards the Gulf with low pressure
maintaining over the region into early next week as multiple upper
level shortwaves into the mean upper trough act to reinforce the
pattern. The notable outlier with the main low on Friday is the
12z UKMET which is much faster than the better guidance consensus.
After Friday though, the 12z CMC is stronger with triple point
redevelopments into/south of the Gulf. The GFS and ECMWF are more
consistent with both each other and the ensemble means so the WPC
blend for the first half of the period was based on these two
deterministic solutions.
Another low should cross well south of the Aleutians this weekend
with another system dropping into the Bering Sea by early next
week. With both, there are some timing and strength differences
between the various models so an ensemble mean solution is
preferred for now as the details continue to worked out. This
approach helps to maintain reasonable continuity from yesterdays
forecast, as well farther downstream across the CONUS.
...Pattern Overview and Weather/Hazard Highlights...
Two deep low pressure systems, one south of the Panhandle and the
other in Bristol Bay, on Friday will continue to bring moderate to
locally heavy precipitation (rain near the coast, snow in the
higher elevations) to parts of the Alaska Peninsula, southern
Coast, and Panhandle region Friday into Saturday. The backside of
the low may also continue some gusty winds for parts of the
Aleutians and AKPen on Friday as the low weakens and slides
southeastward. A couple of triple point developments should act to
reinforce mean low pressure across the Gulf through next weekend
maintaining 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, upper level ridging should keep
daytime highs as much as 10 to 20 degrees above normal into next
weekend with some moderation of temperatures by early next week as
the ridge begins to break down.
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
Hazards:
- High winds across portions of the Aleutians, Thu, Oct 21.
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