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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2021Z Dec 05, 2018)
 
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Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
321 PM EST Wed Dec 05 2018

Valid 12Z Sun Dec 09 2018 - 12Z Thu Dec 13 2018

...Guidance Assessment...

The 06Z GEFS/00Z ECMWF ensemble mean have converged to become in
better agreement in the medium range period. The operational
models still have run-to-run inconsistency, but agree with the
overall pattern. WPC based its blend on mostly the ensemble means,
but still used a small portion of both the 12Z GFS/00Z ECMWF.

...Pattern Overview and Weather Highlights/Hazards...

The beginning of the medium range period starts with an amplified
upper ridge extending across southeast Alaska into the Interior.
Models are in agreement that this feature will weaken through the
weekend as an amplified trough digs across the coastline of
southeast Alaska, British Columbia and the West Coast.
Additionally, the ECMWF/GFS show the northern stream trough energy
along with the mid-upper level trough entering the Bering Sea late
in the weekend and into early next week. The ensemble means
showing the northern stream trough energy digging across Alaska
into early Sunday while the closed upper low approaches the Bering
Sea. By Monday, the upper low sets up in the Bering Sea/western
Alaska and will stay put through midweek. The GEFS/ECMWF ensemble
means both show a deep surface low moving across the Aleutians and
into the Gulf of Alaska on Monday into Tuesday. The ensemble means
both show the closed low hugging the southeast coastline of Alaska
by Tuesday morning--with the 12Z GFS also being in proximity to
the means.  The 00Z ECMWF places the surface low farther south. By
Wednesday, another strong system will approach the western
portions of the Aleutians.

Southern and southeastern Alaska can expect a wet, active pattern
at the end of the weekend through most of next week as multiple
systems move across the Gulf of Alaska. Heavy precipitation could
be possible, especially with the deep storm moving through the
Gulf of Alaska on Tuesday. The northern tier of Alaska will stay
dry while moderate chances of precipitation will continue for the
Aleutians.

Reinhart


WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can be found at:

http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
http://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html