Extended Forecast Discussion NWS Weather Prediction Center College Park MD 239 PM EDT Thu Aug 15 2019 Valid 12Z Sun Aug 18 2019 - 12Z Thu Aug 22 2019 ...Guidance/Predictability Assessment and Weather Highlights/Threats... Flow becomes rather zonal over the CONUS Sunday as low pressure lifts toward Hudson Bay. The movement of this eastern Canadian low and a western Canadian low that persists over northern coastal BC into the middle of next week are the main weather makers over North America with ridging building again over the southwest CONUS. The 00Z/06Z GFS and 00Z ECMWF are in good agreement into Day 6/Wednesday before the operational 00Z ECMWF ejects the western Canadian low into the Canadian Prairies which by 22/12Z is 10 degrees longitude east of the 00Z ECENS mean trough axis which is 10 degrees east of the 06Z GEFS trough axis. The trough over the eastern CONUS will send cold fronts into pooled moisture and instability causing convective thunderstorms, though no particular areas of heavy rain stand out at this time. Above normal temperatures will persist across the southern CONUS through Days 3-7 with abnormal warmth in the northeast continuing into Wednesday until the next cold front pushes through. The WPC medium range product suite was mainly derived from the 06Z GFS/00Z ECMWF through Day 5, then heavier toward the 06Z GEFS/00Z ECENS means. 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: - Flooding possible across portions of the Central Plains and the Middle Mississippi Valley. - Flooding occurring or imminent across portions of the Northern Plains. - Excessive heat across portions of the Southwest, Tue-Thu, Aug 20-Aug 22. - Excessive heat across portions of the Southern Plains into the Lower Mississippi Valley, Sun-Mon, Aug 18-Aug 19. 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