Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Thu Nov 08 2018 Valid 12Z Sun Nov 11 2018 - 12Z Thu Nov 15 2018 ...Great Lakes/OH Valley/Appalachians to interior Northeast Early Season Snow Threat... ...Guidance/Uncertainty Assessment... GFS/ECMWF and GEFS/ECMWF ensemble solutions are well clustered into early next week, but become increasing varied with smaller scale system details into next mid-late week when a composite blend of ensemble means is preferred. This solution maintains good WPC continuity. ...Weather Highlights/Threats... A storm track to the northeast Pacific/Gulf of Alaska maintains an amplified ridge axis aloft along/offshore western North America into early next week. Downstream clipper low track and favorable dynamics will squeeze out a swath of snow in cooled air of the Great Lakes/Northeast. Meanwhile, potent weekend shortwave digging through the Intermountain West/Rockies will favor a lead snow burst over the south-central Rockies Sunday to spill into the Plains as aided by cold post-frontal upslope flow. The upper trough will amplify over the central U.S. early next week with increasing northern and southern stream phasing to the lee of the amplified but gradually inland shifting upstream ridge. Lead wave/frontal genesis and deep moisture return will fuel heavy rain/convection expansion northward across the east-central then eastern U.S. Moisture feeding back into a sharpening baroclinic zone meanwhile presents an organized snow threat through the Appalachians/Ohio Valley, with ample lake effect enhancement lee of the Great Lakes. There is continued uncertainty with respect to the lead coastal/inland low track and western extent of the main precipition shield/cold air with recent ECMWF runs offering a more inland track than more coastal tracks from recent GFS runs. A larger percentage of GEFS and ECMWF ensemble members favor the coastal solution but the minority subset of more inland solutions cannot be rules out considering the amplitude and westward position of the main mid-upper level trough. Ensemble means offer a decent compromise at this point. Overall, there is a threat for heavy Great Lakes/OH Valley/Appalachians to interior Northeast early season snows. Well upstream, Pacific trough energy and height falls start to work into the Northwest early-mid next week as the lead/amplified ridge aloft gradually/finally shifts inland. This supports an increased chance for precipitation including modest elevation snows. 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