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