Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Sat Sep 15 2018 Valid 12Z Tue Sep 18 2018 - 12Z Sat Sep 22 2018 ...Pattern Overview and Weather Highlights/Hazards... The medium range forecast period begins Tuesday with a trough centered near the West Coast, an upper level ridge over the south-central U.S., and a mid-upper level trough over the Appalachians. This trough forces the post-tropical remnants of Florence to eject along with a lead swath of heavy rainfall across the northeastern states to then deepen offshore into the Canadian Maritimes and northern Atlantic. The south-central U.S. upper ridge shifts to the southeast states later week as flow from the Rockies to the Northeast flattens as a series of impulses progress eastward over the U.S. northern tier in the wake of Florence. This forces a wavy cold front down through the mid-latitudes that upstream combines with Gulf of Mexico return inflow and dynamic upper support to focus development of an increasingly widespread north-central U.S. heavy rainfall pattern into mid-late week and ample post-frontal cooling. Underneath, there is also indication some influx of eastern Pacific and Gulf of Mexico sourced tropical moisture may work across Mexico to fuel increased rainfall potential infringing into the Southwest U.S. late week. ...Guidance/Predictability Assessment... Beyond Florence, there is decent large scale pattern agreement in the preferred ensemble means, with the greatest differences noted in individual runs/models with the evolving mid-upper level trough near the West Coast and the timing/amplitude of shortwaves ejecting over the U.S. northern tier. Schichtel WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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