Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
528 PM EST Wed Dec 22 2021
Valid 12Z Sun Dec 26 2021 - 12Z Thu Dec 30 2021
...Overview...
The extended range forecast over Alaska through the middle of next
week will continue to be dominated by a persistent and anomalously
strong upper level ridge and surface high pressure over the
northeast Pacific. Multiple shortwaves/storm systems are expected
to track around the western and northern periphery of the high,
and the high sinks some to the south by the end of the forecast
period. Rounds of light to moderate snow will be possible across
portions of the Interior with these systems weaken as they track
inland.
...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 as a more energetic storm track from eastern
Siberia erodes the ridge some. The biggest model differences
early on are apparent with the 12Z CMC, which is much faster than
the model consensus with the storm system tracking across the
central/northern mainland, and these differences continued
thereafter, so it was not part of the model blend for this
forecast cycle. Elsewhere, the GFS becomes stronger with a trough
entering the southwestern mainland by next Wednesday and continues
further as it tracks over the northern Gulf region, thus eroding
the ridge axis more.
Taking these factors into account, a GFS/ECMWF/UKMET blend was
used through Monday, and increased use of the ensemble means while
retaining some of the GFS/ECMWF along with some previous WPC
continuity.
...Weather/Hazard Highlights...
A storm system and associated cold front originating from the
Bering and western Aleutians is forecast to move quickly across
interior sections of the mainland Sunday and weaken by Monday.
Moisture advection ahead of the front will support patchy areas of
moderate to locally heavy snow across the Seward Peninsula, the
southern part of the Brooks Range, and eastward toward the
Fairbanks area and the central Interior. Some of this snow will
likely be accompanied by strong winds, leading to blowing snow and
localized blizzard conditions, particularly in mountain passes.
Another round of accumulating snow will be possible by next
Tuesday/Wednesday depending on the track of the next storm system
entering the Bering. In the temperature department, frigid
conditions are expected for eastern and northern portions of the
mainland this weekend, with the greatest anomalies expected for
inland portions of the southeast Panhandle region. There should
be a moderating trend commencing by Monday and a return to above
normal readings by the early to middle part of next week for
central and western areas.
Hamrick
Hazards:
- Heavy snow across portions of mainland Alaska, Sun, Dec 26.
- Heavy snow across portions of mainland Alaska, Tue, Dec 28.
- Much below normal temperatures across portions of the Alaska
Panhandle, Sat-Tue, Dec 25-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