Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
751 PM EDT Wed Apr 20 2022
Valid 12Z Sun Apr 24 2022 - 12Z Thu Apr 28 2022
...Guidance/Predictability Assessment...
The extended range period over Alaska features a weakening surface
low over the Gulf while a couple of systems move into the Bering
Sea and near the Aleutians. With the Gulf low, the latest models
continue to show some timing/placement differences, but a general
model blend seems to serve as a good starting point. Later in the
period, there is question on how quickly the low exits into
western Canada, but there is some general consensus that low
pressure in some form should meander in the Gulf as another system
approaches upstream. Meanwhile, a deep surface low just south of
Kamchatka on Sunday/Day 4 will drift very slowly eastward towards
the western Bering, but may eventually weaken early next week as
another system to its south moves in. By day 6, some larger
problems begin to arise in the evolution of a shortwave rounding
the base of broader troughing in the Bering Sea and what
eventually becomes a surface low south of the Alaska Peninsula by
day 8. The GFS is a little weaker and faster than the ECMWF and
brings a surface low along the Aleutians around day 7, while the
12z ECMWF is much sharper with the wave and spins up a surface low
which moves well south of the Aleutians. The 12z CMC track is also
south of the Aleutians but significantly faster than the ECMWF and
GFS and was not included in the blend for the second half of the
period. The ensemble means support something a little slower
anyways, with a (albeit weaker) placement in between the GFS and
ECMWF. Interestingly, by day 8/Wednesday, the low position is
pretty reasonably clustered between the GFS, ECMWF, CMC so its
more a case of models taking a different evolution, but with a
similar end result. The WPC forecast for the second half of the
period leans more on the ensemble means to help mitigate these
differences. Some of the deterministic GFS and ECMWF were
maintained through day 8 through just for a little added system
definition.
...Overview Weather/Hazard Highlights...
Low pressure in the Gulf will continue some light to locally
moderate precipitation across the southern Coast and Panhandle
regions, which should wane with time as the low weakens and pushes
into western Canada. Mainly light precipitation will progress
across the Aleutians associated with a couple of cold fronts
through the period and broad troughing shifting east through the
Bering. Most of the Mainland should remain dry, save for some
scattered activity moving into the western half of the state ahead
of the Bering Sea trough. Temperatures across the Mainland should
be mostly above normal and trending warmer through the period.
Southern regions, from the Aleutians to the Panhandle, should
remain near or below average owing to increased clouds and
precipitation.
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