Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
659 PM EST Wed Dec 07 2022

Valid 12Z Sun Dec 11 2022 - 12Z Thu Dec 15 2022

...Overview...

The latest runs of the deterministic models show a small
improvement with a few features at different time periods, however
the overall pattern has a large degree of forecast spread that
remains to be resolved. The general consensus depicts a low
pressure of moderate amplitude lift into the western Gulf and
slowly tracks north and east. This feature will usher in a steady
plume of deep moisture that will result in moderate precipitation
that may be heavy at times from the Alaska Peninsula Sunday,
across the Kenai Peninsula and surrounding area Monday and from
the Valdez area and points east on Tuesday. Stronger gap winds may
also arise as the low hangs out in the eastern Gulf. Generally
light to moderate precipitation along with strong winds will
spread over portions of the western/southwestern Alaska as
shortwave energies pass from eastern Siberia across the Bering
Sea. Although there continues to be variance with the ridge axis
location, this feature has the most confidence through the
extended forecast. With it progged to settle in over the eastern
part of the state and into western Canada, colder air will reside
over portion of the Southeast and eastern Mainland later in the
period.

...Guidance/Predictability Assessment and Preferences...

Initial smaller-medium scale systems involve a wave/frontal system
over the Bering Sea/Aleutians, low pressure that may track along
the northwest coast of the Bering Sea, and low pressure off the
southeastern coast/Panhandle. Finally, low-predictability
shortwave details will have a say in the details of low pressure
initially over or near the Gulf of Alaska. The latest runs of the
guidance continue to show a large degree of spread in amplitude,
location and progression with several features but most notable is
the system that should reach south of the Aleutians by early
Saturday. For early next week the guidance has offered a general
signal for one or more significant surface lows within an area
from the northwestern Pacific into the Aleutians and western
Bering Sea. The GFS depicted a notable slowing with the North
Pacific low and the GEFS mean slowed a bit as well while the CMC
trended a little more progressive similar to previous runs of the
GFS.

The WPC preferred blend began with a general consensus of the
ECWMF/CMC/UKMET/GFS. Beyond Day 4 the UKMET was omitted. The
ensemble means were introduced during Day 5 and steadily increased
to about 50% by the end of the extended period. The previous
forecasts utilized near 70% weighting of the means by Day 7/8 so
this is a small improvement. 

...Weather/Hazards Highlights...

Well below normal temperatures will be in place over portions of
southern/eastern Alaska as surface high pressure settles over
portions of the mainland into western Canada early on. In
contrast, a majority of the northwest half of the state is
expected to maintain above normal temperatures, or moderate toward
normal through the end of the forecast period. This gradient of
surface pressure will likely lead to the presence of locally
strong gap winds over the Gulf of Alaska/northeastern Pacific
Ocean this weekend onward along the southern coast and Panhandle.
The models continue to struggle coming to a consensus with the
North Pacific low pressure that may affect the Aleutians and
potentially parts of the western/southern mainland during the
weekend into early next week, but there has been slight
improvement. The latest trends continue to have areal averages of
1 to 2+ inches as it skirts eastward with isolated higher
maximums. Once the precipitation moves inland or into areas of
higher terrain it will likely transition over to all snow. Snow
accumulations may end up be several inches daily with near/above 1
foot in the mountains. Finally, another system may affect some
areas over the Aleutians and Bering Sea early next week with
enhanced precipitation and wind but again the specifics are very
uncertain at this time.

Campbell


Hazards:
- Heavy precipitation across portions of mainland Alaska, Sun, Dec
11.
- Heavy precipitation across portions of mainland Alaska and the
Aleutians, Sat, Dec 10.
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Mon, Dec 12.
- High winds across portions of mainland Alaska, Sun, Dec 11.


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