Extended Forecast Discussion NWS Weather Prediction Center College Park MD 305 AM 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 and merging of a developing frontal wave from the Mid-Atlantic with the extratropical remnants of Tropical Storm Nestor. This scenario has high predictability. 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 n-central Rockies Wed/Thu. Height falls should then act to carve out an amplified central U.S. upper trough later week. Pattern evolution uncertainty grows quickly however, lower forecast confidence. Latest guidance trends are mixed, but there is an overall signal showing southern stream separation to some degree later week into next weekend as the main trough shifts over the central states with a possibility of closed low formation that would drastically up the ante with respect to subsequent rainfall potential and runoff threat from the South northeastward into the Eastern Seaboard with deep return of Gulf of Mexico and Atlantic mositure. WPC progs have trended to show such potential. This is with consideration of the amplitude of upstream upper ridging and as the next main kicker upper trough does not bring unsettled weather/locally enhanced precipitation through the Northwest until next weekend, so wavelength spacing with the downstream system seems sufficient to allow for at least some southern stream separation. 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