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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2030Z Jan 15, 2019)
 
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Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
330 PM EST Tue Jan 15 2019

Valid 12Z Sat Jan 19 2019 - 12Z Wed Jan 23 2019

A multi-model signal shows the blocking pattern over Mainland
Alaska transitioning a broad mean trough settling over the
western/central Pacific and a building ridge over the eastern
Pacific extending into northwestern North America. There is a
general consensius pointing to one or more periods of enhanced
precipitation/winds from the Aleutians across the Alaska Peninsula
and southern coast to the Panhandle. The best performing guidance
over the past couple of forecast packages was a compromise of the
ECWMF and CMC.

In collaboration with the Alaskan forecast offices, choose to
utilize the ECMWF and CMC for this forecast package. These two
models continue to depict the ridge over northern Alaska pushing
northward as a low tracks from northwest Canada westward into
northern Alaska. The GFS maintains this feature further East and
does not reflect the recent pattern trend.

A strong system is expected to track northward into the Gulf of
Alaska during the weekend.  The full model/ensemble envelope has a
lot of east-west spread so there is still a risk of meaningful
adjustment in future forecasts. Upper troughing that overspreads
the western/central Pacific will favor evolution of multiple low
pressure centers most likely to track along or just south of the
Aleutians.

The best agreement continues for one wave near the western
Aleutians as of early Fri and then development of a stronger low
south of the central Aleutians during the weekend.  Thereafter
models and ensembles show a variety of ideas involving leading
triple point wave(s) to the east/northeast as well as for
additional western Pacific features that may interact with or
displace leading low pressure. 

Campbell/Rausch


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