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Alaska Extended Forecast Discussion
 
(Latest Discussion - Issued 0007Z Dec 07, 2022)
 
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Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
706 PM EST Tue Dec 06 2022

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

...Overview...

The ensemble means have been fairly persistent with portraying a
series of upper-level features of moderate progression and
amplitude through the extended period. Individual deterministic
model solutions have varied significantly the past few days and
both the ensemble means and their parent models have had a lot of
run-to-run variability and/or trending for embedded features. This
is particularly the case for one or more systems that could affect
areas from the Aleutians through the western/southern mainland,
but also applies to specifics within a general signal for
increased storminess over and possibly east/north of the
northwestern Pacific by early next week. 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.  12Z model trends have been toward slower overall
progress of strongest low pressure relative to the means. The WPC
preferred blend began with a general consensus of the
ECWMF/CMC/UKMET/GFS. Beyond Day 4 the inclusion of the ensemble
mean increased (while dropping the UKMET and reducing the
weighting of the ECWMF, GFS and CMC); reaching approximately
30-50% by Day 5/6 and 50-70% means by Day 7/8. This approach
maintains the conservative approach while maintaining WPC forecast
continuity.

...Weather/Hazards Highlights...

The most confident part of the forecast appears to be with the
establishment of well below normal temperatures over
southern/eastern areas as surface high pressure settles over
portions of the mainland into western Canada. 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.
Guidance is still resolving important details for North Pacific
low pressure that may affect the Aleutians and potentially parts
of the western/southern mainland during the weekend into early
next week. Model trends have been increasing the potential for
some areas to see meaningful precipitation and some brisk to
strong winds, especially along the southern portion of the state.
Some moisture could eventually reach as far east as the Panhandle.
  Most of the solutions indicate daily amounts of 1 to 2+ inches
as it skirts eastward, however a couple are hinting the 3 to 7+
may impact portions of the Kenai Peninsula, Kodiak Island and the
southern Coast. There are also question marks about the eastward
influence of a system that may track well west of the northwestern
mainland, with some potential (though for now in the minority) for
a brief period of increased precipitation and wind.  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/Rausch


Hazards:
- Heavy precipitation across portions of 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