Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
508 PM EST Fri Dec 24 2021
Valid 12Z Tue Dec 28 2021 - 12Z Sat Jan 1 2022
...Overview...
The block pattern with the large upper ridge and surface high over
the northeast Pacific early in the week is expected to gradually
weaken and settle southward by the middle to end of the week.
This will result in the transition from an amplified to a more
quasi-zonal flow pattern by the end of the forecast period. 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, with perhaps a third system over the Gulf by Friday or
Saturday.
...Overview and Guidance Evaluation...
Models and ensembles are in excellent synoptic scale agreement
through Wednesday across the Alaska domain. The 12Z GFS is
slightly stronger with the shortwave trough entering the northern
Gulf Wednesday night, but is similar to the CMC and ECMWF
regarding timing. The main difference is the much faster UKMET,
which is not favored given its lack of ensemble support.
There is reasonable agreement with the next organized storm
emerging from the Bering late in the week, and also across the
Arctic with a broad upper low in place. The ECMWF is stronger
with a trailing disturbance on New Year's Day across the Aleutians.
Taking these factors into account, a GFS/ECMWF/CMC blend was used
through mid-week, and slightly greater use of the ensemble means
while retaining some of the CMC/ECMWF/GFS along with some previous
WPC continuity to close out the week.
...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 20+ degrees above normal
for many areas. Unlike last week, the Arctic Coast and the North
Slope may miss out on the milder temperatures as readings will
likely stay closer to climatological averages with the storm track
staying farther south. Below average temperatures remain likely
for much of the southeast Panhandle region through the middle of
the week with an arctic air mass entrenched over western Canada.
Hamrick
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle,
Wed, Dec 29.
- Heavy snow across portions of mainland Alaska, Tue, Dec 28.
- Much below normal temperatures across portions of the Alaska
Panhandle, Mon-Tue, Dec 27-Dec 28.
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