Extended Forecast Discussion NWS Weather Prediction Center College Park MD 137 AM EST Wed Jan 15 2020 Valid 12Z Sat Jan 18 2020 - 12Z Wed Jan 22 2020 ...Significant Weekend Winter Storm Threat from the Upper Midwest to the Northeast... ...Guidance/Predictability Assessment... A dynamic upper trough tracking from the Plains to the Northeast will spawn a significant weekend low from the Midwest to New England. Models and ensembles show solid agreement with the storm and a composite blend coupled with the National Blend of Models seems to offer a very reasonable forecast in a pattern with above normal predictability/continuity. By early-mid next week, forecast spread increases in a generally more benign weather pattern over the nation. Given this spread, the WPC forecast blend trended to the more compatable and consistent GEFS/NAEFS/ECMWF ensemble means. This maintains good continuity. ...Weather/Hazard Highlights... The guidance signal remains strong for a significant weekend snowfall from the Upper Midwest/Great Lakes to the Northeast, with a combination snow/sleet/freezing rain also possible to the south of the all-snow area. A progressive swath of frontal/warm sector rains/convection are likely into Saturday from the lower MS Valley northeastward to the East, where dammed cold air retreats northward ahead of the low in a potentially messy transition. Lake effect snow will linger behind the low in the reinforcing cold air flow. Upstream, the inland approach of northeast Pacific upper troughing should be shielded by a warming/stabilizing upper ridge building over the West. This may mainly limit periods of precipitation to the Pacific Northwest. Downstream, uncertain trough energies will dig to the lee of the upper ridge into the cooled east-central states. Moisture will be limited in the wake of the lead storm, but expect lingering lake effect snows and some potential to induce western Atlantic frontal waves given sufficient upper trough amplification. Schichtel Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are 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