Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
654 PM EST Sat Dec 18 2021
Valid 12Z Wed Dec 22 2021 - 12Z Sun Dec 26 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 western
periphery of the high. This ridge axis builds northward across
the Bering and western Alaska by Christmas weekend as a blocking
pattern tries to develop. Episodes of light to moderate snow are
expected across portions of the mainland.
...Guidance Evaluation and Preferences...
Similar to yesterday, models and ensembles are in excellent
agreement on the large high over the North Pacific centered near
45N/160W for much of the extended period, with perhaps a slight
southward drift by next weekend. The greatest model uncertainties
reside with shortwave impulses/surface lows tracking northeastward
on the western/northern periphery of the ridge axis, and whether
any of these impulses might be able to erode the northern ridge
axis over the northern half of Alaska. The CMC solution indicates
the best potential for this to happen on Thursday, while the
GFS/ECMWF indicate a relatively weak shortwave reaching northwest
Alaska by Saturday. Except for a stronger disturbance over far
northeast Alaska early in the forecast period, the UKMET is
reasonably close to the model consensus.
Taking these factors into account, the WPC forecast is primarily
derived from a UKMET/GFS/ECMWF/ensemble mean blend through Friday,
and then ECMWF/some GFS/increased ensemble means for next weekend.
...Weather/Hazard Highlights...
The coldest temperatures during this forecast period are expected
to be across the northeast quadrant of the state where light winds
and a strong surface inversion are expected to be in place.
Periods of mainly light snow are likely across much of the western
half of the state associated with warm air advection aloft from
the low pressure systems passing over the Bering Sea. Given the
strong ridge in place over the Gulf/North Pacific, no areas of
heavy precipitation are currently expected for coastal portions of
southern Alaska nor the southeast Panhandle region.
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
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