Extended Forecast Discussion NWS Weather Prediction Center College Park MD 503 PM EDT Fri Jul 10 2020 Valid 12Z Mon Jul 13 2020 - 12Z Fri Jul 17 2020 ...Excessive Heat Across Much of the Southern US to Mid-Atlantic Next Week... ...Overview and Guidance/Predictability Assessment... With the jet stream and associated storm track lifting into northern tier and southern Canada for much of next week, the main headline will be the spreading and prolonged intense summertime heat toward the East Coast. Troughing initially over the Northeast will linger until about Tuesday before an area of low pressure west of James Bay surges a warm front through the region. Overall, the models were in fairly good agreement with the synoptic pattern. The main outlier was the 06Z GFS, which evolved the Northeast trough much slower and also had a faster evolution with shortwaves parading through southern Canada mid to late week. A blend of the 00Z ECMWF/GFS/CMC/UKMET was therefore utilized with increasing weights given to the ECENS/GEFS by day 5-7 as predictability and confidence dropped off due to the quasi-zonal flow. ...Weather Pattern/Hazard Highlights... Front over the East Coast will slowly lift northeastward on Tuesday, opening southwesterly flow that will bring in the very warm/hot temperatures toward the end of the week, especially over the Mid-Atlantic where mid to upper 90s are possible next Thursday. A weak cold front over the Great Lakes may skirt through the Northeast Thu-Fri and hold back temperatures to only a few degrees above normal. A more vigorous front on Monday will push through the Northern Plains and Upper Midwest with a chance of showers/thunderstorms and locally heavy rain. The unsettled weather will continue along to the south of the boundary (central Plains/Corn Belt/western Great Lakes) with generally dry conditions elsewhere over the CONUS except Florida. Temperatures near and above record highs are likely over the Southwest/Texas on Monday with widespread 100+ readings. As the upper ridge moves and expands eastward, above normal temperatures will be likely from the Rockies to the East Coast, centered along I-70 (~Denver to Baltimore). Widespread mid-90s to low 100s are likely with higher heat indices. Overnight temperatures may only fall into the mid 70s to near 80 in urban areas. Fracasso/Taylor 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 Hazards: - Heavy rain across portions of the Upper Mississippi Valley and the Northern Plains, Mon-Tue, Jul 13-Jul 14. - Flooding occurring or imminent across portions of the Northern Plains. - Excessive heat across portions of California and the Southwest, Mon, Jul 13. - Excessive heat across portions of the Southeast, the Lower Mississippi Valley, and the Southern Plains, Mon-Tue, Jul 13-Jul 14. - Excessive heat across portions of the Southeast, the Middle Mississippi Valley, the Lower Mississippi Valley, and the Tennessee Valley, Tue-Thu, Jul 14-Jul 16. - Excessive heat across portions of the Southern Appalachians, the Mid-Atlantic, and the Central Appalachians, Thu-Fri, Jul 16-Jul 17. 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