Extended Forecast Discussion NWS Weather Prediction Center College Park MD 331 PM EDT Fri Jul 19 2019 Valid 12Z Mon Jul 22 2019 - 12Z Fri Jul 26 2019 ...Excessive Heat Episode Winds Down Over The Mid-Atlantic... ...Overview and Weather Highlights/Threats... A hot and humid airmass across the eastern half of the CONUS from the weekend will continue to be suppressed south to the Gulf Coast under a developing upper trough and associated cold front Monday through Tuesday. The cold front will continue to be a focus for widespread convective thunderstorms as it pushes south through the southern Plains, Tennessee Valley, and Mid-Atlantic Monday night and to the Gulf Coast Tuesday. The front looks to slow or stall as waves of weak low pressure progress along the front over the southern Mid-Atlantic Monday night into Wednesday. Moisture and instability pooling ahead of this front and frontal waves should enhance rainfall, with heavy downpours and resultant flash flooding concerns. The cold front will stall over the Gulf Coast through midweek and likely bring relief to both heat and drought conditions in the Southeast. However, the presence of a stalled front along the Gulf Coast in July should lead to a localized flash flood risk. Temperatures behind the front will fall below normal across the central to southern Plains to the mid-lower MS Valley and southeast owing to how far south the front penetrates through these areas. Continued upslope flow to the southern Rockies as the cold front sags south Monday night into Tuesday could lead to localized flash flooding. A ridge persists from the Four Corners to the Canadian Prairies into Wednesday before the next low/trough from the Pacific Northwest begins to over top it. Expect monsoonal convection over the Desert Southwest and Intermountain West through at least midweek. ...Guidance/Predictability Assessment... There continues to be overall good large scale agreement among global deterministic and ensemble guidance through the middle of next week with the setup of a low and trough over the Pacific Northwest, a ridge over the interior West, and a Hudson Bay low with a trough extending south across the eastern U.S. The Pacific Northwest ejects east into Canada and over the top of the ridge Wednesday into Thursday with heights rebounding in the Pacific northwest. The closed anticyclone persists over the central to southern Rockies, and mid-upper trough remains over the northeast and Mid-Atlantic. A weakness with a 500 mb trough drifts west from the Gulf of Mexico into southern TX. The timing and amplitude differences of the upper troughs are small enough to warrant a preference to deterministic models through Day 5 with inclusion of some 06Z GEFS and 00Z ECENS means for Days 6 and 7. The larger differences toward the end of next week involve the handling of cyclone energy over Canada and over the northeast Pacific with the Canadian ensembles much more varied than the GEFS or ECENS. The best agreement is with the persistent anticyclone over the Four Corners by next Friday. Jackson 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 Lower Mississippi Valley, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, and the Southern Plains, Tue-Thu, Jul 23-Jul 25. - Heavy rain across portions of the Northeast, the Central Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, and the Ohio Valley, Mon-Tue, Jul 22-Jul 23. - Flooding occurring or imminent across portions of the Lower Mississippi Valley, the Upper Mississippi Valley, and the Northern Plains. - Flooding likely across portions of the Upper Mississippi Valley and the Northern Plains. - Excessive heat across portions of California and the Southwest, Wed-Fri, Jul 24-Jul 26. - Excessive heat across portions of the Southeast and the Mid-Atlantic, Mon, Jul 22. 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