Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1150 AM EDT Sun Sep 08 2019 Valid 12Z Wed Sep 11 2019 - 12Z Sun Sep 15 2019 ...Potential for record heat to continue for the lower Mississippi Valley and Southeast... ...Overview and Guidance Evaluation/Preferences... An upper-level ridge is forecast to remain rather entrenched from the lower Mississippi Valley to the Southeast through much of the medium range. Meanwhile, initially splitting upper flow from the eastern North Pacific into western North America will consolidate as a stream of relatively vigorous upper shortwaves traverse the CONUS northern tier. Farther south, an easterly wave is forecast to approach Florida and the coastal southeastern U.S. by the upcoming weekend, traversing the southern periphery of the expansive upper ridge. For the start of the medium range period, a blend of the 00Z ECMWF/CMC and 06Z GFS was used, which represented consensus well with the synoptic features across the Northern Plains. For Day 5 onward, model differences became more significant, particularly with the evolution of troughing over the Pacific Northwest and northern Rockies. The 06Z GFS was considerably faster with the shortwave energy coming out on Day 6 and 7 (Sat-Sun) while the ECMWF/CMC were slower and a bit more amplified. This matched better with the ensemble means and consensus, so less weight was given to the GFS late in the forecast period, with more weight toward the ECENS/NAEFS ensemble means. The 00Z ECMWF/CMC offered some utility for day 6-7, so some of it was incorporated into the blend as well. ...Weather Highlights/Threats... Heavy rain will be possible across much of the Northern Plains and Upper Midwest Wed-Thu in association with a deepening surface low pressure system crossing the region. Models suggest the potential for at least a couple inches of rainfall across a relatively wide area. The easterly wave approaching Florida and the Southeast U.S. by late in the week is expected to increase shower and thunderstorm activity, with locally heavy rains possible. Increasing rain, potentially moderate to heavy, will also be possible across the mountain ranges of the Pacific Northwest by late week as upper troughing progresses into the region. Hot conditions are expected to persist across portions of the south central and southeastern U.S. through much of the upcoming week. 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. Several record high temperatures are possible each day, especially from the lower Mississippi Valley to the Southeast where highs may soar well into the 90s, perhaps approaching 100 deg at a couple locations. Ryan/Taylor 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