Extended Forecast Discussion NWS Weather Prediction Center College Park MD 312 PM 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... An upper trough sliding from the Rockies to the Northeast Days 3-5 will develop a significant low in the lee of the Rockies, which tracks across the Plains/Midwest Friday/Saturday and into New England by Sunday. Models continue to show very good agreement with both timing and intensity of this storm system, so a general deterministic model blend worked well for days 3-5, leaning mostly on the 00z ECMWF and 06z GFS. This results in above normal confidence in this system, and maintains great WPC continuity. By days 6-7, forecast spread increases with upper troughing approaching the West Coast. The GFS/GEFS are more amplified and a bit faster than the ECMWF/ECENS. Given this spread, the forecast blend trended more towards the ensemble means, with smaller contributions from the GFS and ECMWF. ...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 interior Northeast with a combination snow/sleet/freezing rain also possible to the south of the all-snow area. Some locations within this zone 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. Santorelli/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 Hazards: - Heavy precipitation across portions of the Plains, the Mississippi Valley, the Southern/Central Appalachians, the Tennessee Valley, the Great Lakes, the Mid-Atlantic, the Northeast, the Southeast, and the Ohio Valley, Fri-Sun, Jan 17-Jan 19. - Heavy rain across portions of the Central Plains, the Lower Mississippi Valley, and the Southern Plains, Fri, Jan 17. - Heavy snow across portions of the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Fri-Sat, Jan 17-Jan 18. - Heavy snow across portions of the Great Lakes, the Mid-Atlantic, the Northeast, and the Central Appalachians, Sat-Sun, Jan 18-Jan 19. - Flooding possible across portions of the Southeast, the Middle Mississippi Valley, the Great Lakes, the Ohio Valley, and the Upper Mississippi Valley. - Flooding occurring or imminent across portions of the Lower Mississippi Valley, the Northern Plains, the Tennessee Valley, the Middle Mississippi Valley, the Great Lakes, and the Ohio Valley. - Flooding likely across portions of the Middle Mississippi Valley, the Great Lakes, and the Ohio Valley. - Much below normal temperatures across portions of the Northern Plains and the Northern Rockies, Fri-Sat, Jan 17-Jan 18. - Much below normal temperatures across portions of the Central Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Northern Plains, Sun-Tue, Jan 19-Jan 21. - High significant wave heights for coastal portions of California and the Pacific Northwest, Sat-Sun, Jan 18-Jan 19. - Much below normal temperatures across portions of the Alaska Panhandle and mainland Alaska, Fri-Sun, Jan 17-Jan 19. - Much below normal temperatures across portions of the Alaska Panhandle, Fri-Sat, Jan 17-Jan 18. 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