Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
529 PM EST Thu Dec 23 2021
Valid 12Z Mon Dec 27 2021 - 12Z Fri Dec 31 2021
...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.
Multiple shortwaves and low pressure systems from the Bering and
the Aleutians will likely bring a few rounds of snow for much of
the mainland.
...Overview and Guidance Evaluation...
The 12Z model guidance suite remains in excellent overall
agreement on the dominant upper ridge situated over the North
Pacific near 45N/155W through early next week, and then shifting
southward by mid-week and beyond as a more energetic storm track
from eastern Siberia begins eroding the ridge. The UKMET is
stronger with both the storm system tracking across the state
Sunday night and also with the system approaching from the Bering
on Wednesday, although the positions look reasonable. By Thursday
and Friday, the 12Z GFS is considerably stronger with the ridge
across the Aleutians and Gulf region and loses support from its
ensemble mean, whereas the CMC/ECMWF agree on a more suppressed
ridge with more shortwave energy tracking eastward across southern
Alaska and the Aleutians.
Taking these factors into account, a GFS/ECMWF/CMC blend was used
through mid-week, and increased use of the ensemble means while
retaining some of the CMC/ECMWF along with some previous WPC
continuity to close out the week.
...Weather/Hazard Highlights...
Multiple rounds of snow are likely across central and northern
portions of the mainland through the middle of the week, with the
greatest potential for this late Tuesday and into early Tuesday.
Some locations across the Interior may become warm enough for a
mix of rain/snow or even plain rain in the warm sector of the low.
Farther south across the Aleutians and extending eastward to the
Kenai Peninsula, more rain/snow showers will be possible for the
end of the week, although specifics are unclear on timing and
magnitude at this time. In terms of temperatures, the greatest
cold anomalies are expected across the southeast Panhandle region
early in the week, with an arctic air mass entrenched over the
Yukon and British Columbia yielding highs at least 15-20 degrees
below normal. Elsewhere across the state, widespread above
average temperatures are likely for the Interior and extending
north of the Brooks Range, with the potential for a few record
highs.
Hamrick
Hazards:
- Heavy snow across portions of mainland Alaska, Sun, Dec 26 and
Tue, Dec 28.
- Much below normal temperatures across portions of the Alaska
Panhandle, Sun-Tue, Dec 26-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