Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
520 PM EST Thu Dec 16 2021
Valid 12Z Mon Dec 20 2021 - 12Z Fri Dec 24 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 periphery of
the high. A slow moving polar low near 75 degrees north is also
expected to remain in place for much of next week. A strong cold
front is expected to cross most of the state early in the week and
bring a return to colder temperatures after above average readings
on Monday.
...Guidance Evaluation and Preferences...
The 12Z model guidance suite is in good overall agreement on
Monday across the Alaska domain. The upper high centered south of
the Alaska Peninsula has the greatest model agreement through the
extended forecast period, and the polar low north of the Arctic
Coast is also well represented by the guidance. Model differences
become apparent with shortwave energy crossing the Aleutians and
northern Gulf, and the UKMET in particular stands out from the
consensus by Monday night and into Tuesday with a much faster and
stronger trough over the northern Gulf of Alaska that is not
favored by the ensemble means. The 12Z GFS is also quite strong
with this same feature, but closer in timing with the weaker
CMC/ECMWF solutions. Model differences continue for the next
system to cross over southern Alaska/Gulf region by Thursday, and
the CMC differs more so with a considerably stronger ridge axis
extending north into the Interior, with the incoming trough quite
a bit slower. Taking these factors into account, the WPC forecast
is primarily derived from a CMC/GFS/ECMWF/ensemble mean blend
through Wednesday, and then ECMWF/some GFS/increased ensemble
means for next Thursday and Friday.
...Weather/Hazard Highlights...
Precipitation, mainly in the form of snow, is likely for western
and central parts of the mainland through early Tuesday, given the
increasing deep layer moist southwesterly flow into the state to
the west of the Pacific ridge. From the Brooks Range southward
into parts of western and central Alaska, snow may be heavy over
terrain favored by strong southwesterly winds on Monday. Strong
low level winds are expected, which along the coast may even lead
to areas of coastal flooding. Areas with a combination of snow
and strong winds could see blizzard conditions. Another round of
precipitation may affect the Aleutians and southwestern Alaska
around next Wednesday-Thursday as another Pacific storm system
approaches.
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.
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
Hazards:
- Heavy snow across portions of mainland Alaska, Sun, Dec 19.
- Heavy snow across portions of mainland Alaska, Sun-Mon, Dec
19-Dec 20.
- Heavy snow across portions of mainland Alaska, Mon, Dec 20.
- High winds across portions of mainland Alaska and the Aleutians,
Sun, Dec 19.
- High winds across portions of mainland Alaska, Sun-Mon, Dec
19-Dec 20.
- High winds across portions of mainland Alaska, Tue-Wed, Dec
21-Dec 22.
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