Extended Forecast Discussion NWS Weather Prediction Center College Park MD 145 AM EDT Mon Aug 10 2020 Valid 12Z Thu Aug 13 2020 - 12Z Mon Aug 17 2020 ...Overview and Guidance/Predictability Assessment... Models and ensembles agree 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 later period upper trough will begin to develop just off the West Coast, but with only modest rainfall potential into the Pacific Northwest. The WPC medium range product suite was derived from a blend of reasonably well clustered guidance from the 18 UTC GFS/GEFS, 12 UTC ECMWF/ECMWF ensemble mean, the 02 UTC National Blend of Models and WPC continuity. Blend weight emphasis on the models days 3/4 (Thu/Fri) was transitioned mostly to the ensemble means by day 6/7 (Sun/next Mon) consistent with growing forecast spread as predictability lowers from above average to near average. ...Weather/Hazard Highlights... A wavy lead front will focus daily thunderstorms with some heavy downpours across 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. The wavy trailing front back through the north-central U.S. will meanwhile also act to focus convective development as impulses and favorable upper jet support interact with lower level return flow and pooling moisture and instability. The draped front will increasingly lift northward through the period in prelude to cold frontal approach from the West. This will further trigger episodes of strong to severe thunderstorms with locally heavy downpours. 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 local flow details. 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