Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1208 PM EDT Sun Oct 20 2019 Valid 12Z Wed Oct 23 2019 - 12Z Sun Oct 27 2019 ...Guidance/Uncertainty Assessment and Weather Highlights/Threats... An energetic pattern supports several significant lower 48 weather systems this week. A lead upper trough will lift through the Northeast midweek as a main deepened surface low works into Canada. Lingering rains/runoff issues over the Northeast may be enhanced by interaction of a developing frontal wave from the Mid-Atlantic, which will likely merge with the extratropical remnants of Tropical Storm Nestor from off the East Coast. Guidance also agrees that the flow pattern will meanwhile reamplify well upstream as upper impulses/jet energies dig progressively inland over the rapidly cooling West to support some heavier snows into the north and central Rockies Wed/Thu. Height falls should then act to carve out an amplified central U.S. upper trough later this week. Pattern evolution uncertainty grows quickly thereafter, resulting in low forecast confidence for the eastern half of the country. Latest guidance continues to indicate two possible scenarios by this weekend: (1) A more amplified upper trough draws in tropical moisture from the Gulf and results in a low pressure system that spreads heavy rainfall well inland, as indicated by the ECMWF and CMC solutions; or (2) less flow separation between the northern and southern streams will keep a cold front moving steadily across the eastern U.S., as indicated by the GFS. All of the ensemble means (GEFS, EC mean, CMC mean) so far are more in line with the second scenario, however. The WPC morning grids were derived from a blend of yesterday's 12Z ECMWF, 00Z EC mean, the 06Z GFS and 06Z GEFS together with WPC continuity for Days 6 and 7. But for Days 3 to 5, the 00Z ECMWF was used in instead of yesterday's 12Z ECMWF. Kong/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