Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1143 AM EDT Sat Sep 28 2019 Valid 12Z Tue Oct 01 2019 - 12Z Sat Oct 05 2019 ...Heavy rainfall possible from the Southern/Central Plains to the lower Great Lakes by 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 ... ...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 progressive 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 is forecast to amplify as 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. A blend of the 00Z ECMWF/GFS/UKMET was used as a forecast starting point through much of the forecast period, with most emphasis among these three solutions placed on the ECMWF, which was consistently well-centered in the ensemble spread at least through days 5-6 (Thu-Fri). The 06Z GFS was much faster than the guidance consensus with the eastward progression of shortwave energy across the Northern Plains/Upper Midwest next Wed-Thu, and this solution was discarded. Model consensus was relatively good with the next amplifying trough expected to reach the West Coast Thu, with variation among solutions largely confined to the amplitude of the feature. As this feature moves inland from the northern Rockies to the Northern Plains Fri-Sat, the ECMWF was the most well-centered solution within the ensemble spread, and showed good agreement with the ECENS/NAEFS means. Spread increases by late in the forecast period (Sat) as another upper trough approaches the Pacific Northwest with model run-to-run variability also increasing. Thus, weighting of ensemble means was boosted substantially by day 6 (Fri) and especially day 7 (Sat). ...Weather Highlights/Threats... A wavy surface front will focus precipitation from the Southern/Central Plains to the lower Great Lakes by midweek. Flow around the western periphery of the strong ridge over the southeastern U.S. will draw tropical moisture northward where it will interact with the frontal boundary. The potential exists for a few inches of rain in a band from the Central Plains to the lower Great Lakes during the middle of the week, with flash flooding a possibility. Meanwhile, deep-layer easterly flow and an influx of deeper tropical moisture will promote an increase in showers and thunderstorms over Florida. 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 above normal with numerous daily records expected to be broken into late next week. Ryan/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