Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1207 AM EST Tue Jan 14 2020 Valid 12Z Fri Jan 17 2020 - 12Z Tue Jan 21 2020 ...Significant Fri-Weekend Winter Storm Threat from the Upper Midwest to the Northeast... ...Guidance/Predictability Assessment... The WPC medium range product suite valid Friday-Sunday was mainly derived from a composite blend of very well clustered model and ensemble guidance and the 00 UTC National Blend of Models. This maintained great WPC continuity in a stormy pattern with above normal forecast predictabilty. Increased blend weighting to more compatable and consistent ensemble means in a more benign pattern Mon/Tue amid growing forecast spread/uncertainty. ...Weather/Hazard Highlights... The track of an amplified upper trough/height falls and frontal system will spread a moderate swath of terrain enhanced snow across the Great Basin and Rockies Fri. Upstream Pacific systems will bring periods of rain/mountain snow to the Northwest, with a trend for precipitation to shift northwestward and offshore Sun-next Tue as heights rise. The aforementioned upper trough will continue to the east/northeast into the weekend, becoming negatively tilted by the time it reaches the Northeast. With associated deepening low pressure slated to track from the High Plains through the Midwest and then New England and the Canadian Maritimes, the guidance signal is strengthening for the threat of significant snowfall from the Upper Midwest into the Northeast with other wintry precip types also possible to the south of the all-snow area. Some locations should see wintry precip before a changeover to rain. Meanwhile locations in the Mid-Mississippi Valley and Lower Ohio Valley will have to monitor effects from rainfall given the heavy rain experienced over the past week. Other areas from the south-central Plains northeastward could see some runoff issues with locally moderate-heavy warm sector rainfall. Lake effect snow will linger behind the system in the flow of reinforcing cold air. 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