Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1254 AM EDT Sun Jul 26 2020 Valid 12Z Wed Jul 29 2020 - 12Z Sun Aug 02 2020 ...Overview... Summer heat and a subtropical high pressure area slowly retrogrades into the Four Corners region during the medium range period, with upper ridging also building across much of the Rockies and Southern Plains. Meanwhile, an upper low in eastern Canada should help to maintain troughing across the Northeast as a frontal boundary settles from the Mid-Atlantic to the Central Plains. Out West, troughing becomes established mid to late week along or just off the West Coast which will drive a series of fronts into the Northwestern states. ...Weather/Hazard Highlights... A stationary frontal boundary draped from the Mid-Atlantic region back into the Central Plains will become the focus for numerous showers and thunderstorms, and locally heavy rainfall, through much of the period. Models continue to indicate the potential for more organized moderate to heavy rainfall possible from the middle Mississippi Valley into the Tennessee/lower Ohio Valleys Wednesday into Friday as weak upper level energy rounds the top of the Southern tier ridge. Additional moderate to heavy rainfall is also possible along the Carolina coasts through Friday near a weak area of low pressure along the front. Temperatures from the Central Plains to Tennessee Valley should be about 5 to 10 degrees below normal with abundant cloud cover and moisture. Elsewhere, daytime highs should hover near normal. Across the extreme south, combined heat and humidity should result in triple digit heat indices for many, especially across portions of the Southwest, Gulf Coast, and the Southeast/Florida. ...Guidance/Predictability Assessment... The guidance continues to show relatively good agreement on the overall large scale pattern, with expected variances in the smaller scale and less predictable features, especially later in the period. The weak spot for model agreement is across the Western U.S. mainly regarding timing of shortwave energy as it enters the Northwest coast mid-period. WPC used a blend of the GFS/ECMWF deterministic solutions through day 5, leaning more heavily on the ensemble means days 6-7. Some moderate percentage of the ECMWF was maintained through the entire period just to maintain some level of definition to the forecast. This approach also maintains good WPC continuity. Santorelli 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