Extended Forecast Discussion NWS Weather Prediction Center College Park MD 248 PM EDT Sun Aug 09 2020 Valid 12Z Wed Aug 12 2020 - 12Z Sun Aug 16 2020 ...Overview and Guidance/Predictability Assessment... Guidance continues to agree reasonably well that two main closed upper lows will track gradually eastward over Canada as trough energies along with temperature moderating and convection focusing fronts work across the northern half of the U.S.. To the south, upper ridging will prevail over much of the nation's southern tier, with some record triple-digit maximum temperatures possible from the Desert Southwest to the southern High Plains. Elsewhere, models agree that a weak upper trough will linger just off the West Coast. The WPC medium range product suite was derived from a composite of best clustered guidance from the 00 UTC ECMWF, CMC, 06 UTC GFS, together with the 06Z GEFS, 00Z EC ensemble means and the 00 UTC NAEFS in a pattern with normal to above normal predictability. Uncertainty increases toward the end of next week particularly over the northern Plains. More of the ensemble means were used for Days 6 and 7 to handle the uncertainty. ...Weather/Hazard Highlights... A wavy front will focus thunderstorms with some heavy downpours possible across the Ohio Valley on Wednesday before shifting farther east into the Mid-Atlantic and the Carolinas for the rest of the week. Expect these scattered thunderstorms to be most active everyday during the late afternoon to evening hours. Over the northern Plains, the trailing portion of the wavy front is forecast to return as a warm front as a low pressure wave begins to form. This will help trigger episodes of thunderstorms, possibly strong, across the northern Plains into the upper Midwest Thursday and Friday. Meanwhile, the Southeast/Florida will continue to experience diurnal convection of varying intensity. Within the broad area of shower and thunderstorm potential there will be some areas of heavy rainfall contingent on less predictable flow details. Elsewhere, the weak upper trough just off the West Coast is not expected to bring any precipitation inland. Kong/Schichtel 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