Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
521 PM EST Sat Dec 25 2021
Valid 12Z Wed Dec 29 2021 - 12Z Sun Jan 2 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. Two well
defined low pressure systems from the Bering and the Aleutians
will likely bring a few rounds of snow for much of the mainland.
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...
Models and ensembles are in reasonably good synoptic scale
agreement through most of the forecast period across the Alaska
domain. The main exception to this is the 12Z CMC that is likely
too flat with the shortwave trough crossing southern Alaska as
early as Wednesday, and also considerably slower with the next and
larger storm system crossing the Aleutians by Thursday. The UKMET
has trended closer in line with the model consensus compared to
yesterday's much faster solution. By Friday night and into the
weekend, the GFS becomes more amplified with the trough over the
Gulf and this solution evolves into a big closed low, whereas the
ensemble means would suggest this trough/upper low to be farther
north and not quite as strong.
Taking these factors into account, a GFS/ECMWF/UKMET blend was
used through early Friday 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 New Year's weekend.
...Weather/Hazard Highlights...
Periods of light to moderate snow, and heavy snow for mountainous
areas, appears likely across a majority of the state for the
Tuesday/Wednesday time period, and maybe warm enough for rain
across the lower elevations of southwestern Alaska with strong
warm air advection in place in the warm sector of the low. A
second round of organized precip is also on the horizon for the
end of the week as another low approaches from the Bering.
Depending on what eventually develops over the northern Gulf by
next Friday, some areas of heavy precipitation may develop over
southern Alaska and the southeast Panhandle region.
In terms of temperatures, much of the Interior will get to enjoy
more above average temperatures for much of next 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 should miss out on the milder temperatures as readings will
likely stay closer to climatological averages or slightly below
with the storm track staying farther south. Below average
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