Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Sun Aug 11 2019 Valid 12Z Wed Aug 14 2019 - 12Z Sun Aug 18 2019 ...Overview and Guidance/Predictability Assessment... Quasi-zonal flow over the northern half of the lower 48 will amplify later this week as a deeper trough digs into the West Coast and ridging strengthens over the south-central U.S. This seems likely to favor mean troughing downstream in the eastern U.S. Energy from the western trough may split by next weekend, with part moving eastward and part hanging back along the western U.S, though scenario details have lower predictability given ample recent run to run continuity issues. A composite blend incorporating the 18 UTC GFS/GEFS mean and 12 UTC ECMWF/ECMWF ensemble mean was mainly used as the starting point for the WPC medium range product suite, leaning heavily on ensembles due to the continued smaller-scale uncertainties in the flow. Overall, this blend provided good WPC product continuity. ...Weather Highlights/Threats... A wavy lead frontal system will shift southward through the eastern and central states, stalling out over the South/Southeast later week. Widespread showers and thunderstorms including a threat of local cell training/runoff issues are expected to move southward from the Mid-Atlantic to focus into the Southeast/Gulf Coast from midweek onward as deepened Gulf moisture streams into the vicinity of the front. Upstream, upper trough amplification over Northwest/northern Rockies mid-later this week and robust system/height fall ejections into the north-central U.S. next weekend should both provide dynamics and instabilities supportive of periods of locally enhanced rainfall and thunderstorms. Expect warmer than average pre-frontal temperatures for the Gulf Coast states/Southeast into mid-later week. There is a threat of excessive heat with widespread record high minimum temperatures. Additionally, the Southwest to Southern Plains should also experience hot temperatures through the period under the upper high/ridge. Tate/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