Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1158 AM EDT Thu Jul 18 2019 Valid 12Z Sun Jul 21 2019 - 12Z Thu Jul 25 2019 ...Widespread Excessive Heat Persists into Monday... ...Overview and Weather Highlights/Threats... A hot and humid airmass across the eastern half of the CONUS will be suppressed south to the Gulf Coast under a developing upper trough Sunday through Tuesday. Excessive heat ahead of the associated cold front will continue to warrant heat headlines until the cold frontal passage. The abbreviated heat wave will remain problematic for those working or recreating outdoors, individuals sensitive to heat, especially the elderly and animals. The cold front will be a focus for widespread convective thunderstorms as it pushes south from the Central Plains, Midwest and Northeast Sunday night and into the southern Plains and Southeast Monday. The front looks to slow or stall with frontal wave development over the southern Mid-Atlantic Monday through Tuesday. Moisture and instability pooling ahead this cold front and frontal waves should enhance rainfall amounts and increase the risk for flash flooding, particularly where the front slows. The cold front will eventually sag toward or to the Gulf Coast by midweek and likely bring relief to both heat and drought conditions in the Southeast, though the persistence of the front for several days with convergence of Gulf moisture looks to lead to at least localized flash flooding concerns. North of the tail end of this cold front there will be enhanced upslope flow to the central/southern Rockies as it sags south Sunday night into Tuesday which could lead to localized flash flooding. A ridge builds from the Four Corners to the Canadian Prairies Sunday night through Tuesday and persists at least through Wednesday before the next low/trough from the Pacific Northwest begins to over top it. Expect monsoonal convection over the Desert Southwest under this developing ridge starting Monday and expanding up the Intermountain West through at least midweek. ...Guidance/Predictability Assessment... There is overall good large scale agreement among global deterministic and ensemble guidance in the early to middle parts of next week with the setup of a strengthening trough over the Pacific Northwest, a building ridge over the interior West, and a trough digging from the Great Lakes. Details with shortwave energy, particularly as it rounds the ridge and into the eastern trough is understandably varied among guidance. The 00Z and 06Z GFS/GEFS is more amplified with the eastern trough and brings it to the Gulf Coast earlier than the 00Z ECMWF/ECENS. However, overall the timing and strength differences are small enough to warrant a general deterministic model blend with the 00Z/06Z GFS and 00Z ECMWF/CMC/UKMET for days 3-5 with equal weighting of the 06Z GEFS/00Z ECENS for days 6 and 7 along with some of the deterministic 06Z GFS/00Z ECMWF/CMC. 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 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