Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Sat Sep 28 2019 Valid 12Z Tue Oct 01 2019 - 12Z Sat Oct 05 2019 ...Heavy rainfall potential from the central Plains to the lower Great Lakes in the middle of next week... ...Anomalous warmth to persist over the central to eastern U.S., while very chilly conditions moderate somewhat in the northern and northwestern states ... ...Pattern Overview and Guidance/Uncertainty Assessment... Model guidance this evening continues to indicate a deep upper low over the northwestern U.S. will eject eastward toward the Great Lakes during the medium-range period. This will lead to a more zonal pattern across the northern tier states by the end of next week as a strong upper ridge gradually weakens over the Southeast. Meanwhile, another upper trough moving toward British Columbia will likely amplify when it reaches the Pacific Northwest late next week. A wavy front is forecast to gradually move across the central and eastern U.S. next week, with a swath of heavy precipitation possible from the central Plains to the lower Great Lakes in the middle of the week. Ensemble consensus remains quite good through the medium-range period. The 18Z GFS shows the formation of an anomalous low across the Northeast toward the end of next week. This low was not supported by other deterministic solutions nor the ensemble means. Nevertheless, ensemble solutions suggest the formation of a frontal wave somewhere in the vicinity of northern Mid-Atlantic to the Northeast late next week. This is reflected on the Day 7 prognostic chart. The WPC grid package is comprised of a consensus of the 12Z ECWMF, and the 18Z GFS through day 5, with a higher percentage given to the 12Z EC mean. Increasing weight was given to the 12Z EC mean beyond day 5, mixing in with some 18Z GEFS and 12Z NAEFS. ...Weather Highlights/Threats... A wavy trailing front will become the focus for precipitation across the central Plains to the lower Great Lakes by midweek as the upper-level flow becomes more zonal. Flow around the western periphery of the strong ridge over the southeastern U.S. will draw tropical moisture from the eastern Pacific Ocean northward and then interact with the frontal boundary. Potential exists for a few inches of rain along a band across the central Plains to the lower Great Lakes during the middle of the week, with the possibility of flash flooding. Deep-layer easterly flow, associated will the decaying Tropical Storm Karen, will promote an increase in showers and thunderstorms over Florida. Please monitor NHC forecasts for the latest information regarding Karen. Very chilly conditions over the western U.S. into Northern Plains are expected to moderate somewhat by early next week. On the other hand, many locations from the Gulf Coast to New England will be averaging 10-20F warmer with numerous daily records expected be broken. Kong 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