Extended Forecast Discussion NWS Weather Prediction Center College Park MD 112 AM EDT Sat Jul 20 2019 Valid 12Z Tue Jul 23 2019 - 12Z Sat Jul 27 2019 ...Overview and Weather Highlights/Threats... A cold front will continue to be a focus for widespread showers and thunderstorms as it pushes south through the southern Plains, lower MS Valley, and southeast Tuesday and to the Gulf coast by Wednesday. However, the presence of a stalled front along the Gulf Coast in July should lead to showers and storms, along with a localized flash flood risk. Temperatures behind the front will 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. Waves of weak low pressure progress along the front over the southern Mid-Atlantic Tuesday and Wednesday. Moisture and instability pooling ahead of this front and frontal waves should enhance rainfall, with heavy downpours and resultant flash flooding concerns. Continued upslope flow to the southern Rockies as the cold front sags south Monday night into Tuesday could lead to localized flash flooding. Expect monsoonal convection over the Southwest and Intermountain West each day as pockets of moisture and instability occur around the periphery of the large scale high. Several model/ensemble members depict a 700-500 mb wave crossing the northern Plains Fri and into the upper MS Valley/upper Great lakes Sat. This should increase probability of showers/storms in these locations/days. ...Guidance/Predictability Assessment... There continues to be overall good large scale agreement among global deterministic and ensemble guidance through the middle of next week with the setup of a trough over the Pacific Northwest, a ridge over the interior West, and a Hudson Bay low with a trough extending south across the eastern U.S. The Pacific Northwest trough ejects east into Canada and over the top of the ridge Wednesday into Thursday with heights rebounding in the Pacific northwest Fri until the next upper trough approaches Sat 27 Jul. 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 deterministic 18z GFS/12z-00z ECMWF along with the 18z GEFS and 12Z ECENS means for Days 3 through 7. The larger differences toward 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 by Friday 26 Jul and drifting into AZ Sat 27 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