Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 545 PM EDT Sat Oct 10 2020 Valid 12Z Wed Oct 14 2020 - 12Z Sun Oct 18 2020 ...Overview and Guidance/Predictability Assessment... A favored blend of compatible guidance of the 12 UTC GFS/ECMWF and 12 UTC GEFS/ECMWF ensemble means was mainly used to provide a starting point for the WPC Alaskan medium range product suite. Most weighting in the blend was applied to the ECMWF Wed/Thu and then increasingly the ECMWF ensemble mean amid growing forecast spread and uncertainty. Emphasis on the ECMWF then ECMWF ensemble mean shifted the blend into the more amplified side of the full envelope of solutions for Alaskan mainland to Gulf of Alaska upper troughing. This collaborative solution still seems prudent given high upper ridge amplitude upstream in most guidance. This maintains reasonable WPC continuity and takes into account the less likely scenario of the 12 UTC Canadian that offers an even more amplified/closed outlier solution. Canadian run to run variance is less than stellar. ...Weather/Threats Highlights.. Strong upper ridge amplification is expected up through the Bering Sea to into the Arctic Ocean early next week. This should allow Arctic flow energy to carve out an amplifying downstream upper trough down over an increasingly unsettled and cooled/locally snowy North Slope and Interior through mid-later next week before the moderating main upper ridge is slated to shift eastward and inland. Forecast spread has improved over the past few runs, but guidance remains a bit varied with the details of the upper trough with better details to emerge into shorter range time scales. This Arctic energy may also amplify sufficiently to overcome early-mid week southern stream troughing/systems over the Gulf of Alaska and support phasing and coastal low/system deepening. Coastal areas of southern and southeast Alaska will remain unsettled/showery in this transitional pattern and some heavier precipitation and seas are increasingly possible. Meanwhile, forecast spread is relatively low and the guidance signal is growing in support of having the Aleutians turn more stormy heading into next weekend as amplified upper trough energies offer potential to work deepening systems into the region in the wake of the eastward shift of the main lead upper ridge. Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can also be found at: https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html