Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
528 PM EST Fri Dec 17 2021
Valid 12Z Tue Dec 21 2021 - 12Z Sat Dec 25 2021
...Overview...
The main theme going into next week will be a dominant upper
ridge/surface high pressure over the North Pacific with multiple
shortwaves/storm systems tracking around the northern and eastern
periphery of the high. A slow moving polar low near 75-80 degrees
north is also expected to slowly lift north across the Arctic
Ocean and the ridge axis builds northward across the Bering and
western Alaska by Christmas. A strong cold front is expected to
cross most of the state by Tuesday and bring a return to colder
temperatures after above average readings this weekend and Monday.
...Guidance Evaluation and Preferences...
The 12Z model guidance suite is in good overall agreement on
Tuesday across the Alaska domain, and there has been a trend for a
stronger shortwave/surface low over the northeastern Gulf and
southeast Panhandle region since yesterday, with the exception
here being a weaker CMC solution. The upper high centered south
of the Alaska Peninsula has the greatest model agreement through
the extended forecast period, and should remain nearly anchored in
place near 45N/160W. The polar low north of the Arctic Coast is
also well represented by the guidance. Model differences become
more noteworthy by Thursday with both timing and magnitude
differences with shortwave energy emerging from eastern Siberia.
Given the strong signal in the ensemble means for an elongated
north-south ridge axis across the Bering late in the forecast
period, and the potential for some blocking to develop, the
incursion of stormy weather from the western Bering and eastern
Siberia should hold off through the end of the week.
Taking these factors into account, the WPC forecast is primarily
derived from a UKMET/GFS/ECMWF/ensemble mean blend through
Wednesday night, and then ECMWF/some GFS/increased ensemble means
thereafter.
...Weather/Hazard Highlights...
Temperatures are expected to be pleasant for this time of year and
thus well above average across much of the mainland to begin the
week, with the potential for some daily record highs to be
established. Some inland locations that have been below freezing
for many weeks might get readings above 32 degrees briefly early
in the week before reality sets in after a strong cold front moves
through. Strong and gusty winds are also likely for portions of
the Arctic Coast through midweek. Latest model guidance suggests
that warmer weather may try to make a return to portions of the
Interior by the end of the week, and this would likely be
accompanied by warm air advection snow from the western mainland
to the Brooks Range, with the potential for several inches of
accumulation. Lingering rain/snow showers are likely across the
southeast Panhandle region on Tuesday as the low pressure system
departs the region.
Hamrick
Hazards:
- Heavy snow across portions of mainland Alaska, Mon, Dec 20.
- High winds across portions of mainland Alaska, Tue-Fri, Dec
21-Dec 24.
- High winds across portions of mainland Alaska, Tue-Wed, Dec
21-Dec 22.
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