Extended Forecast Discussion NWS Weather Prediction Center College Park MD 244 PM 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 good enough agreement to warrant a total deterministic model blend for days 3 and 4 to handle this system. Beyond this, the weather across the CONUS should be fairly quiet through day 7 as high pressure builds across much of the nation and various weak shortwaves with low predictability cross through the West. A short wave dropping down behind the initial Northeastern U.S. trough may induce a western Atlantic frontal wave by day 6-7, but there are differences in the details of this and how close this may come to the East coast and what, if any, sensible weather effects this brings. For day 5 and beyond, prefer an increasing ensemble mean blend which smooths out the detail differences in the deterministics. ...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. Strong surface Canadian high pressure dives into the Central U.S. bringing much below normal (greater than -20F anomalies) to portions of the northern High Plains into the Midwest this weekend. High pressure moderates as it pushes east early next week, with below normal anomalies not as strong and a return to more winter like conditions for much of the East Coast. 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, with the exception of some lake effect snows lingering into early next week. 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 Central/Northern Plains, the Middle/Upper Mississippi Valley, the Great Lakes, the Ohio Valley, the Southern/Central Appalachians, the Mid-Atlantic, and the Northeast, Sat-Sun, Jan 18-Jan 19. - Heavy snow across portions of the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Sat, Jan 18. - Heavy snow across portions of the Northeast and the Great Lakes, Sat-Sun, Jan 18-Jan 19. - Flooding possible across portions of the Upper/Middle Mississippi Valley, the Great Lakes, the Ohio Valley, and the Tennessee Valley. - Flooding occurring or imminent across portions of the Lower/Middle Mississippi Valley, the Northern Plains, the Tennessee Valley, the Southeast, the Great Lakes, and the Ohio Valley. - Flooding likely across portions of the Middle Mississippi Valley and the Ohio Valley. - Much below normal temperatures across portions of the Northern Plains and the Northern Rockies, Sat-Sun, Jan 18-Jan 19. - Much below normal temperatures across portions of the Northern/Central Plains and the Upper/Middle Mississippi Valley, Sun-Tue, Jan 19-Jan 21. - High significant wave heights for coastal portions of the Pacific Northwest, Sat-Sun, Jan 18-Jan 19. 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