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Alaska Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1952Z Sep 17, 2018)
 
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Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
352 PM EDT Mon Sep 17 2018

Valid 12Z Fri Sep 21 2018 - 12Z Tue Sep 25 2018

Model/ensemble consensus has been relatively good that the flow
pattern across the North Pacific will become more amplified over
the next week, although some significant differences remain with
respect to the details of specific features. Models still have not
resolved exactly what will happen Fri-Sat with an area of Arctic
shortwave energy initially across the Interior. Given the quickly
amplifying flow, continue to prefer a solution more like the ECMWF
which digs the energy southward across the Gulf and along the
western coast of Canada. Thus, begin the forecast for the extended
period with a majority ECMWF solution during days 4-5. Otherwise,
heights should begin to gradually rise across Alaska by the
weekend as a North Pacific upper ridge axis expands across the
state. The strength of the ridge remains somewhat up for debate
among the guidance, with the 12Z run of the ECMWF really backing
off the upper ridge by early next week with much more progressive
flow taking hold - a solution which seems an outlier compared to
previous ECMWF runs as well as the majority of other
model/ensemble guidance. Assuming the idea of a more amplified
flow pattern by the weekend holds, expect a deepening upper trough
across the Bering Sea with the likelihood for a relatively deep
surface cyclone. Model solutions range widely in the
timing/position of any potential cyclone, however. Thus, trended
the forecast to majority ensemble mean (ECENS/NAEFS) weighting by
later in the extended.

Ryan


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