Extended Forecast Discussion NWS Weather Prediction Center College Park MD 110 AM EDT Fri Jul 09 2021 Valid 12Z Mon Jul 12 2021 - 12Z Fri Jul 16 2021 ...Excessive Southwestern Heat Persists into Next Week... ...Pattern Overview with Weather Highlights/Hazards... The ongoing heat wave under upper ridging will continue for the Great Basin to CA and the Southwest into early next week with temperatures 10-20F above normal through Tuesday. Several daily high temperature records are likely through Tuesday in these areas. The model consensus is leading to gradually lowering heights with a developing modest northwest US trough, with the highest heights drifting south into southern CA/AZ. With high along over the southeast, another area with above normal temperatures will be the mid Atlantic to the lower Great Lakes/NY. This includes the Washington, DC to Baltimore, Philadelphia, and New York City corridor. The forecast indicates potential for showers/thunderstorms over the Southwest/Southern Rockies with pockets of enhanced 700 mb relative humidity in place to support diurnal activity with instability peaking each afternoon/evening. Locally heavy rainfall may occur along a slow moving front in the Midwest to the lower MS Valley on Sunday as fueled by return/pooling Gulf Moisture and instability. A break develops with the front decaying afterward. The next frontal wave brings heavy rainfall potential into Iowa and Missouri Wed and Thu 15 July, possibly developing into the adjacent Midwest and Ohio Valley by the end of next week. ...Guidance/Predictability Evaluation... The WPC medium range product suite was primarily derived from a blend of guidance from the 18 UTC GFS/GEFS, 12 UTC operational ECMWF/Canadian global. The guidance is in better than average agreement in the anticyclone over the southwest and southeast. The primary differences are the timing/amplitude of the 700-500 mb trough over the Northwest coming into the mean upper Midwest and then Great Lakes trough. An equally weighted solution among the 12z ECMWF/12z Canadian/18z GFS/18z GEFS Mean was used to mitigate the differences. Petersen Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook 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