Extended Forecast Discussion NWS Weather Prediction Center College Park MD 413 PM EDT Wed Jul 17 2019 Valid 12Z Sat Jul 20 2019 - 12Z Wed Jul 24 2019 ...Widespread Excessive Heat Threat Through The Weekend... ...Overview and Weather Highlights/Threats... A large portion of the country will remain hot and humid through this weekend under a broad ridge which continues an excessive heat threat. Numerous locations will likely reach, or set new daily high minimum records and some maximum temperature records this weekend into Monday. With high humidity and persistent heat indices of 105 to 115F+, heat headlines will persist. This heat wave may become problematic for those working or recreating outdoors, individuals sensitive to heat, especially the elderly and animals. Relief from the heat for much of the country occurs early next week as upper ridging/heat will build over the west-central states which will allow a trough to develop over the east-central states. An associated cold front will push southeast across much of the central and eastern states; crossing the Midwest Sunday and nearing the Gulf Coast Tuesday night. A last of a series of impulses will track east from the Canadian Prairies and into the northern tier of the U.S. this weekend. This pattern will be favorable for developing showers and thunderstorms capable of producing locally heavy convection/MCS activity over the northern Great Plains/Great Lakes Saturday night before activity focuses more on the cold front Sunday into next week. Locally excessive rainfall may result from the multiple rounds of rain/high rain rates over the northern tier. Guidance continues to suggest the max QPF occurs over the Upper Mississippi Valley and Great Lakes this weekend that spreads into the east-central and southeast states early next week with the trough amplification/cold front. The tail end of this cold front is likely to bring enhanced upslope flow to the central/southern Rockies as it sags south Sunday into next week. Expect renewed monsoonal convection over the Southwest under the developing ridge starting Monday. ...Guidance/Predictability Assessment... Uncertainty is greatest with the strength and positioning of a western Canadian ridge this weekend and the associated effects on the strength and timing of the downstream trough over the eastern U.S. early next week. The WPC medium range product suite was mainly derived from a typical general model blend of deterministic global guidance for Days 3 to 5 with inclusion of the 00Z GEFS and ECENS means for Days 6 and 7. The 06Z GEFS mean lags the 00Z GEFS mean and all other global ensemble means and was therefore excluded from the blend for Day 6 and 7. Jackson/Rausch Hazards: - Heavy rain across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Southern Rockies, the Southern Plains, and the Southwest, Sun-Tue, Jul 21-Jul 23. - Heavy rain across portions of the Mid-Atlantic, the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Northeast, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Mon-Tue, Jul 22-Jul 23. - Heavy rain across portions of the Middle Mississippi Valley, the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Sat-Sun, Jul 20-Jul 21. - Heavy rain across portions of the Southeast and the Mid-Atlantic, Wed, Jul 24. - Flooding occurring or imminent across portions of the Central Plains, the Lower Mississippi Valley, the Upper Mississippi Valley, and the Northern Plains. - Flooding likely across portions of the Central Plains, the Middle Mississippi Valley, and the Northern Plains. - Excessive heat across portions of the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Middle Mississippi Valley, the Upper Mississippi Valley, the Great Lakes, and the Ohio Valley, Sat, Jul 20. - Excessive heat across portions of the Southeast, the Mid-Atlantic, the Northeast, and the Central Appalachians, Sat-Sun, Jul 20-Jul 21. 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