Extended Forecast Discussion NWS Weather Prediction Center College Park MD 120 AM EDT Sat Sep 07 2019 Valid 12Z Tue Sep 10 2019 - 12Z Sat Sep 14 2019 ...Record heat to continue for the Lower Mississippi Valley/Gulf Coast next week... ...Overview and Guidance Evaluation/Preferences... The medium range period begins on Wed with an upper trough in the west and a rather strong ridge (for September) in place across the Southeast. An upper ridge initially in place across west central Canada will result in split flow across western North America, but this ridge should break down by Wed-Thu, eventually allowing stronger westerlies from the higher latitudes to dig southward into the northwestern U.S. Shortwave energy crossing central Canada Tue-Wed is forecast to move a wave of low pressure and associated frontal system across the Upper Midwest and Great Lakes, reaching the Northeast Wed night. The more significant upper trough initially across the West is forecast to move east across the Rockies by Thu and into the Central/Northern Plains Thu night/Fri. Model consensus shows relatively vigorous cyclogenesis occurring across the Northern Plains Wed night/Thu morning ahead of the shortwave crossing the Upper Midwest and moving into central Canada by Thu night/Fri as the surface cold front continues to sweep eastward into next weekend. Finally, as upper flow consolidates by mid to late next week as described above, models show some consensus that another shortwave should dig toward the Pacific Northwest by next Fri, with an associated surface frontal system pressing inland, reaching the Great Basin/Rockies by Sat. A blend of the 12Z ECMWF/18Z GFS served as a forecast starting point during days 3-4 (Tue-Wed), although with more weight toward the ECMWF relative to the GFS due to a low track from the Upper Midwest into the Great Lakes more aligned with the overall model/ensemble consensus. Starting on day 5 (Thu) and continuing through day 7 (Sat), weight of ECENS/GEFS ensemble means was gradually increased, although the deterministic ECMWF maintained some utility at least into day 6 with a solution relatively in line with the ensemble consensus. Model spread with respect to both timing and structure of the shortwave reaching the Northwest late next week was relatively high, with even some timing differences noted between the ECENS/GEFS means which were slower/faster, respectively. Given these, differences, a blend primarily of the ensemble means was thought to represent a reasonable compromise approach by the end of the forecast period. ...Weather Highlights/Threats... Moderate to locally heavy rains will accompany the leading low pressure system across the Upper Midwest/Great Lakes Tue-Wed. The second low pressure system developing across the north central U.S. Wed-Fri may result in a threat for somewhat more widespread heavy rains. Models show a signal for an area of strongly forced rainfall to the north of the surface low track across portions of the northern High Plains, with at least a couple inches of rain possible. Farther south, additional areas of showers and thunderstorms will be possible across much of the central U.S. along/ahead of the cold front, with the potential for at least localized heavy rainfall. Persistent hot temperatures across portions of the south central and southeastern U.S. will be the other significant story in the medium range. High temperatures are forecast to be 5 to 15 deg F above average across a large area from the Ohio Valley to the lower Mississippi Valley and the Southeast through most of next week. Several record high temperatures are possible, especially from the lower Mississippi Valley to the Southeast Ryan 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