Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
304 PM EDT Thu Sep 20 2018

Valid 12Z Mon Sep 24 2018 - 12Z Fri Sep 28 2018

...Guidance and Predictability Assessment...
Models/ensembles continue to struggle with the handling of the
rather complicated/blocky flow from over the Pacific into western
North America next week. Given the inconsistent models and now to
a lesser extent ensemble means, decided in  collaboration with
Alaskan weather offices to rely on a composite of the latest
GEFS/NAEFS/ECMWF ensemble means that maintains reasonable WPC
continuity.

...Pattern Overview and Weather/Hazards Highlights...
It remains the case that the upper pattern will support nearly
stationary high pressure centered just southeast of the Gulf of
Alaska that will inhibit surface frontal progressions from making
clean sweeps eastward. Rather, wavy fronts will get hung up
parallel to the flow on the western periphery of the high
coincident with a persistent moisture conduit to fuel a prolonged
period of clouds/rain to the AKPen and Southern Alaska to into the
northern Panhandle. By midweek next week, reloading troughing
along the Dateline is forecast to deepen/consolidate a surface low
days 7/8 along and south of the stormy Aleutians. This development
is slightly slower than continuity, with recent ensemble means
underestimating later period flow amplitude. The effect is smaller
than yesterday though, so guidance may getting close to the truth.
Confidence is lower than average on specifics/timing of systems,
but near average on the overall larger scale flow pattern.

Schichtel


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