Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
336 PM EDT Wed Sep 19 2018

Valid 12Z Sun Sep 23 2018 - 12Z Thu Sep 27 2018

The models/ensembles continue to struggle with how to handle the
rather complicated/blocky flow over the Pacific into western North
America next week. This affects timing more than amplitude of the
systems embedded in the increasingly meridional flow but some
areas have trended quicker (roughly east of 160W) while areas west
of there have trended slower. Given the inconsistent models and
rather large shifts in the ensemble means (especially the normally
steadfast ECMWF ensemble mean) opted to rely on a blended solution
near the 12Z GFS/06Z parallel GFS with its ensemble mean and the
00Z ECMWF/ECMWF ensemble mean which have forged a reasonable
starting point despite their timing differences.

The upper pattern will support a stationary high pressure south of
the Gulf that will prevent any surface frontal boundary from
making a clean sweep eastward. Rather, the boundary will get hung
up parallel to the flow allowing a prolonged period of clouds/rain
to the AKPen and Southcentral areas into the northern Panhandle.
By midweek next week, reloading troughing along the Dateline is
still forecast to deepen a surface low though this still remains
at day 8 (i.e., one day slower than yesterday). Confidence is
lower than average on specifics/timing but near to above average
on the overall pattern (trough/ridge).

Fracasso


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