Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1206 PM EDT Thu Oct 18 2018 Valid 12Z Sun Oct 21 2018 - 12Z Thu Oct 25 2018 ...Guidance/Predictability Assessment and Weather Highlights/Threats... Model and ensemble forecasts seem reasonably well clustered Sun into Tue, bolstering forecast confidence to above normal levels with preference of a composite guidance solution. The pattern is highly amplified at higher latitudes with a mean mid-upper level trough and surface low/storm solution into Alaska and the Northeast Pacific. Slow translations leads to an infringement of lead height falls into western Canada and the northwest U.S. along with an increasingly precipitation amount and chance of moderate precipitation days 5-7. Rapidly increasing forecast spread later Tue into next Wed/Thu in a transitioning pattern downstream lowers forecast confidence and suggests preference for an ensemble mean blend and continuity. In this later time frame recent GFS runs become much less amplified and more progressive with northern stream flow across Canada and the northern tier of the lower 48 than the ECMWF. I'd favor decently amplified flow inertia and lean at least as amplified as the ensemble means if not quite the ECMWF. At the same time, recent GFS runs also bring much more organized southern stream energy with origin from east Pacific tropical activity than other guidance to produce widespread heavy precipitation well inland over the southern Plains in stark contrast to alternate guidance that holds the bulk of precipitation more into the lower Mississippi Valley and in general closer to the coast and offshore into the Gulf of Mexico. The GFS seems way overdone considering latest NHC input and considering that any tropical system influnce would likely be more disrupted moving inland over the moutains of Mexico. WPC medium range QPF focuses a heavy rainfall threat over the western then central Gulf Coast states. Guidance is in better agreement to bring modest precipitation on the backside up northward through the southern and central rocky states with progression of a main southern stream trough from CA/NW Mexico. Schichtel WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml