Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Sun Sep 16 2018 Valid 12Z Wed Sep 19 2018 - 12Z Sun Sep 23 2018 ...Guidance/Predictability Assessment and Weather Highlights/Hazards... The Weather Prediction Center is now issuing advisories on current Tropical Depression Florence that remains an ongoing catastropic inland heavy rainfall and flash flooding/flooding threat. By Wednesday morning as per coordination with the Ocean Prediction Center, the latest WPC 15 UTC advisory depicts Florence as an emerging extratropical gale off eastern New England and the Canadian Maritimes, with a subsequent later week track over the northern Atlantic as a maritime hazard. Mid-level heights should gradually build across the eastern U.S. in response to a progressive shortwave digging through the north-central U.S. Thursday. This is expected to enhance a threat of heavy rainfall to spread across the north-central U.S. Widespread activity would be fueled by an increasingly deep return flow of moisture from the Gulf of Mexico into the focusinging baroclinic zone and lead low. This pattern should then drive a developing surface cyclone across Quebec by Friday. This and a developing pattern with a series of U.S. northern tier progressive shortwaves favors the driving of a lead and ample cooling/drying front down across much of the west-central to eastern U.S. into next weekend. Strong post-frontal high pressure spilling from Canada will reinforce cold air that supports some northern Rockies snows. Back across the eastern Pacific, a broad ridge extending up into the Gulf of Alaska will help maintain lower heights along the West Coast for much of the period. An initial shortwave is forecast to slide into the Pacific Northwest late Thursday before eventual absorption into the active Canadian northern stream. On its heels should be a more impressive axis of height falls which focuses a longwave trough over the far eastern Pacific next weekend. The 00 UTC ECMWF and Canadian models show substantially more shortwave energy digging over Alaska then northeast Paciifc than the 06 UTC GFS and 06 UTC GEFS. 00 UTC NAEFS/ECMWF ensemble means support a solution trending WPC continuity toward the more amplified/offshore idea into next weekend. Finally, across the Desert Southwest, an area of disturbed weather lifting out of the subtropical Pacific should enhance low/mid-level moisture and rainfall potential across the region. The National Hurricane Center currently suggests an 80 percent chance for tropical cyclogenesis during the next 5 days. 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