Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
653 PM EST Tue Nov 16 2021
Valid 12Z Sat Nov 20 2021 - 12Z Wed Nov 24 2021
...Much below normal temperatures likely across Alaska through the
medium range period...
...Overview and Guidance Evaluation/Preferences...
In general, the global guidance is fairly clustered for at least
days 4 and 5 of the extended forecast; which has been the case the
past few days. In coordination with the local forecast offices,
there was notable shift in the upper level flow pattern in the
global guidance from yesterday's guidance due to the complex
nature of each individual shortwave interaction. Previously, a
shortwave trough was depicted as digging southwest from the
Mainland into the Bering Sea spurring rapid cyclogenesis
downstream over the Gulf of Alaska; whereas now this feature looks
to become blocked by a system approaching the Aleutian Chain
resulting in a not so amplified low over the Gulf. Hopefully the
next couple of runs of guidance will lock on to a direction. In
the meantime, continued continuity by being heavy handed with the
12Z ECWMF/CMC/GFS through day 5 and increasing the weights of the
12Z GEFS/NAEFS/ECWMF ensemble mean through the end of the period.
The use of the means will help mute some of the noise in the later
period, however there is lower confidence on the specifics.
...Weather/Hazard Highlights...
Much of Alaska will continue to have colder than seasonal average
temperatures, especially across the central and southern regions
thanks to surface high pressure becomes established across the
state. Some locations across the western and southern part of the
state will have daily readings as much as 20-30+ degrees below
normal. The temperatures are expected to stay cooler than average,
although they may moderate as the synoptic flow becomes less
amplified. The North Slope will likely remain near, or briefly
above seasonal normal through the extended period.
Precipitation is expected to remain focused over the Aleutians,
along the southern coastal areas and over the Southeast. A
majority of the Interior will remain dry in this pattern. As the
surface low moves through the Gulf there will be periods of
moderate to heavy precipitation over the the Panhandle region.
This pattern also favors flow funneling through the mountain
ranges of southern Alaska; which may lead to strong outflow winds
across Southwest Alaska. Wet and unsettled conditioned will return
as another system tracks into the Aleutians late in the period,
spreading from the Aleutians to locations along the southern coast
and enhancing over the Panhandle by next weekend.
Campbell
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
- Heavy precipitation across portions of the Alaska Panhandle,
Sun-Mon, Nov 21-Nov 22.
- Much below normal temperatures across portions of mainland
Alaska, Fri-Mon, Nov 19-Nov 22.
- Much below normal temperatures across portions of mainland
Alaska, Fri, Nov 19.
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