Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
529 PM EST Sun Dec 26 2021
Valid 12Z Thu Dec 30 2021 - 12Z Mon Jan 3 2022
...Overview...
The block pattern with the large upper ridge and surface high over
the northeast Pacific through the middle of the week is expected
to gradually weaken and settle southward by Friday. A well
defined low pressure system from the Bering and the Aleutians will
likely bring widespread snow for much of the mainland to close out
the week. By next weekend, the ridge is expected to build back
northward across the Aleutians/Bering with perhaps another blocky
pattern developing.
...Overview and Guidance Evaluation...
The 12Z model guidance suite has a good overall depiction of the
large scale pattern through the extended range period as things
become more amplified. The guidance is consistent in breaking
down the North Pacific ridge by the end of the week with a potent
storm system tracking eastward from the Bering. Both the 6Z/12Z
runs of the GFS have been faster with the disturbance entering the
Gulf by Saturday, and the CMC a bit slower and weaker. By Sunday,
the upper ridge over the Bering kicks into high gear along with a
deepening trough over the eastern Gulf. The 12Z ECMWF even
suggests an anomalous closed upper high over the central Bering by
next Monday, and this would basically be a westward displaced
-EPO. This could easily result in a renewed blocky pattern across
the Alaska domain.
Taking these factors into account, a multi-deterministic blend was
used through early Saturday as a starting point in the forecast
process, and slightly greater use of the ensemble means while
retaining primarily some of the 12Z ECMWF along with some previous
WPC continuity for Sunday and into Monday.
...Weather/Hazard Highlights...
Widespread light to moderate snow appears likely across a majority
of the southern half of the state for the end of the week, and
maybe warm enough for rain for the immediate coastal areas along
the eastern Aleutians to the Kenai Peninsula, as an organized low
approaches from the Bering. The surface low is expected to
intensify over northern Gulf by Saturday morning, and thus some
areas of heavy precipitation will likely develop over the
southeast Panhandle region. A drier trend should ensue for most
of the state by Sunday and beyond.
In terms of temperatures, much of the southern portion of the
Interior will get to enjoy more above average temperatures for the
end of the week with less of an inversion in place and highs
running 10-20 degrees above normal for many areas. Unlike last
week, the Arctic Coast and the North Slope will miss out on the
milder temperatures as readings will likely stay below zero from
the Brooks Range and points northward. With the exception of the
Aleutians, bitterly cold temperatures are likely to make a return
to much of the state to begin 2022.
Hamrick
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