Extended Forecast Discussion NWS Weather Prediction Center College Park MD 326 PM EDT Tue Jul 16 2019 Valid 12Z Fri Jul 19 2019 - 12Z Tue Jul 23 2019 ...Widespread Excessive Heat Threat... ...Heat Wave Threat... ...Overview and Weather Highlights/Threats... There is a significant threat for dangerously hot and humid conditions later this week/weekend into early next week within an expansive sector of the nation. Later week hot upper ridging will encompass much of the Southwest and south-central portions of the Rockies and central and eastern U.S. By early next week, upper ridging/heat is expected to build up through the west-central states and begin to gradually moderate downstream down into the east-central U.S. with upper trough amplification and southward sagging of a main northern tier states frontal zone. In the hot sector, widespread locations may tie or set new daily high minimum records and some maximum temperature records. Heat indices will persist in some areas upwards of 105 to 115F+ taking into account high dewpoints, which may lead to some heat advisories issuances. Overtop, a quasi-zonal mean flow pattern develops over the northern-tier of the U.S. late week and for the weekend. A prolonged series of impulses/trough energies will pass over southern Canada and through the U.S. northern tier states with uncertain individual system amplitudes and timings. Showers and thunderstorms capable of producing locally heavy convection/MCS activity will sporadically develop and propagate within a wavy frontal/baroclinic zone across the north-central states, Midwest/Great Lakes and Northeast/Mid-Atlantic. Multiple rounds of rain/high rain rates may lead to locally excessive rainfall as the moisture and instability pools along the slow moving and wavy main frontal boundary. Although the model spread for QPF is not as high as previous cycles, it still lower confidence on where and when the highest amounts occur. Guidance continues to suggest the max QPF occurs over the Upper Mississippi Valley and Great Lakes this weekend that spreads into the east-central states early next week with flow amplification. Also expect renewed monsoonal convection over the Southwest and southern Rockies later period with flow transition. ...Guidance/Predictability Assessment... Latest guidance still depicts a fair amount of uncertainty through the extended period with embedded systems and local convective focus. Accordingly, the WPC medium range product suite was mainly derived from a blend of the reasonably compatable 06 UTC GEFS mean, 00 UTC NAEFS/ECMWF ensemble means, and WPC continuity. Schichtel 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 Central Plains, the Central Rockies, the Central Great Basin, the Southern Rockies, the Southern Plains, and the Southwest, Mon-Tue, Jul 22-Jul 23. - Heavy rain across portions of the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, and the Ohio Valley, Sun-Mon, Jul 21-Jul 22. - Heavy rain across portions of the Great Lakes and the Upper Mississippi Valley, Sat-Sun, Jul 20-Jul 21. - Heavy rain across portions of the Southeast and the Mid-Atlantic, Tue, Jul 23. - 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, the Lower Mississippi Valley, and the Northern Plains. - Excessive heat across portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, the Ohio Valley, and the Upper Mississippi Valley, Fri-Sat, Jul 19-Jul 20. - Excessive heat across portions of the Southeast, the Mid-Atlantic, the Northeast, and the Central Appalachians, Fri-Sun, Jul 19-Jul 21. 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