Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
459 PM EST Sat Dec 03 2022
Valid 12Z Wed Dec 07 2022 - 12Z Sun Dec 11 2022
...Guidance/Predictability Assessment and Preferences...
The guidance shows general agreement concerning the general flow
pattern in and around AK -- a persistent upper low/trough over
eastern Asia, broad ridging across the north-central Pacific and
at times AK, and downstream troughing across the far northeast
Pacific and western North America. The area of better model
agreement remains near the AK Panhandle for a third day. The same
is not true in the Aleutians, where the guidance continues to
struggle with the depth aloft of a couple shortwaves/possible
upper lows and their related cyclone moving through/near the area,
possibly into the Bering Sea. The 12z UKMET was a slow outlier
today, and day-to-day changes in individual pieces of
deterministic guidance continues to be less than ideal. To deal
with the uncertainty, for the 500 hPa heights, pressures, fronts,
and winds, generally used a deterministic heavy blend of the 12z
GFS, 12z ECMWF, and 12z Canadian early on before including up to
60% of the 12z NAEFS mean/00z ECMWF ensemble means thereafter with
tweaks made (lower pressures and increase winds) so that systems
weren't so washed out. This idea maintained reasonable continuity
with Thursday's forecast. The QPF used the 19z NBM and, 12z GFS,
12z Canadian, and 12z ECMWF solutions. The remainder of the grids
were 19z NBM weighted, as usual.
...Weather/Hazards Highlights...
With the flow pattern expected, once the troughing shifts east
across AK, a drying trend should be seen across the interior and
North Slope while wet conditions are expected to be constrained to
the Aleutians, southern coast, and AK Panhandle (which should see
a bulk of the precipitation mid to late week). An interior and
North Slope cooling trend begins next Thursday night initially due
to an upper level trough, but continues afterward due to
convergence aloft between the departing upper trough and a
developing upper ridge across western mainland AK leading to
decreasing cloudiness with cold and dry surface high pressure
system enveloping the interior. Low temperatures are forecast to
fall as low as -30F across the normally colder eastern interior by
next Friday night.
Roth
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