Extended Forecast Discussion NWS Weather Prediction Center College Park MD 107 AM EDT Fri Jul 19 2019 Valid 12Z Mon Jul 22 2019 - 12Z Fri Jul 26 2019 ...Excessive Heat Episode Winds Down Over The Northeast and Mid Atlantic... ...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. 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 waves of weak low pressure progressing along the front over the southern Mid-Atlantic Monday through Tuesday. Moisture and instability pooling near this front and frontal waves should enhance rainfall amounts, with localized heavy downpours and resultant flooding concerns. 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. The front will focus showers and storms along the Gulf coast into Florida. The temperatures behind the front fall below normal across the central to southern Plains to the mid-lower MS Valley and southeast owing to how far south the front penetrates through these areas. There will be enhanced upslope flow to the central/southern Rockies as it sags south Sunday night into Tuesday with resultant showers and storms, 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 trough over the Pacific Northwest, a building ridge over the interior West, and a trough drifting east from the the Great Lakes and Ohio Valley to the northeast and Appalachians. The Pacific Northwest trough moves downstream into Canada next Wed-Thu with heights rebounding in the northwest. The closed anticyclone persists over the central to southern Rockies, and mid-upper trough remains over the northeast and mid Atlantic. A weakness with a 500 mb trough drifts west from the Gulf of Mexico into southern TX. The timing and amplitude differences of the upper troughs are small enough to warrant a blend of the models and ensemble means with the forecasts consisting of an equally weighted average of the 12z ECMWF/12z ECMWF Ensemble Mean/18z GFS/18z GEFS Mean/12z Canadian Global. The larger differences towards the end of next week involve the handling of cyclone energy over Canada and over the northeast Pacific. The best agreement is with the persistent anticyclone over the four corners region (CO/UT/AZ/NM) by next Fri 26 Jul. Petersen 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