Extended Forecast Discussion NWS Weather Prediction Center College Park MD 240 AM EDT Wed Jul 17 2019 Valid 12Z Sat Jul 20 2019 - 12Z Wed Jul 24 2019 ...Widespread Excessive Heat Threat... ...Heat Wave Threat... ...Overview and Weather Highlights/Threats... A large portion of the country will be rather hot and humid this coming week, which bolsters an increasing threat for excessive heat. 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. Numerous locations will likely reach, or set new daily high minimum records and some maximum temperature records. With high humidity and persistent heat indices of 105 to 115F+, there may be some issuance of heat advisories. This heat wave may become problematic for those working or recreating outdoors, individuals sensitive to heat, especially the elderly and animals. Areas north of the ridging will be stuck in a quasi-zonal mean flow pattern, with a series of impulses/trough energies that will track through southern Canada and into the northern tier of the U.S. The specifics for each system continues to be uncertain. However, this pattern will be favorable for developing showers and thunderstorms that will be capable of producing locally heavy convection/MCS activity- sporadically propagating within a wavy frontal/baroclinic zone across the north-central states, Midwest/Great Lakes and Northeast/Mid-Atlantic. Locally excessive rainfall may result from the multiple rounds of rain/high rain rates. 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... Uncertainty on individual features in respect to timing, location and strength continues; therefore persisted in utilizing ensemble means for a starting point. The WPC medium range product suite was mainly derived from a blend of the reasonably compatible 00Z GEFS mean and 12Z NAEFS/ECMWF ensemble means. Campbell 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