Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1128 PM EDT Sat Jul 21 2018 Valid 12Z Wed Jul 25 2018 - 12Z Sun Jul 29 2018 ...Heavy Rain and Flooding for the East... ...Southwest/West heat wave into mid-late week... ...Central Rockies/Plains to Mid-MS Valley Heavy Convection... ...Guidance/Uncertainty Assessment and Weather Threats... It remains the case that forecast predictability remains much above normal in showing an amplified mid-uppper level trough lingering with an axis roughly along 85W into midweek. Deep moisture with pooled precipitable water values upwards of 2" feeding into/ahead of the system and associated/slow moving surface fronts/instability will prolong a pattern favorable for cell training/repeat activity that will continue a threat of locally heavy/excessive rainfall for the Eastern Seaboard. This system will be surplanted by a well defined upstream trough/height falls working across the Great Lakes/Midwest and northeastern U.S. mid-late week whose development will focus lingering heavy rainfall over the Northeast/coastal Mid-Atlantic and trailing to FL/vicinity consistent with dynamic support/frontal progressions. Flash flooding and longer term/larger scale flooding remains possible in the wake of recent rains. A hot mid-upper level ridge meanwhile settled over the Southwest and up over the West along with potential for record maximum temperatures will gradually ease through mid-later this week, but monsoonal moisture could allow for more record high minimum temperatures. A series of impulses rotating within and overtop the ridge offers less predictable timings individually, but each will provide enhanced lift. This may be especially problematic in upper diffluent flow/boundary convergence from the central Rockies/Plains into the mid-MS Valley where convective complexes/thunderstorms will be fueled by inflow pooling moisture and heavy/repeat cells may lead to a local excessive rainfall threat. Much of this medium range forecast remains of high confidence during this cycle, with strong agreement and clustering among the models and ensembles regarding these well defined and slowly/steadily evolving features. Accordingly, the WPC medium range forecast suite was primarily derived from a composite blend of the latest GFS/ECMWF, GEFS and ECMWF ensemble means, the NBM, and WPC continuity. Schichtel WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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