Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM EDT Wed Aug 29 2018 Valid 12Z Sat Sep 01 2018 - 12Z Wed Sep 05 2018 ...Guidance/Predictability Assessment and Weather Highlights/Hazards... Stream split shortwave troughs of uncertain amplitude/timings will continue to feed into western North America. Expect an energetic stream flow to drive modest precipitation over the northwestern U.S. then more in ernest through the north-central and to a lesser extent the eastern U.S. Wavy frontal systems combine with theta-e advection/deepened moisture/instability to fuel periods of heavy convection/MCS activity focusing from the eastern Plains/Mississippi Valley. Additional convection may spread into the Great Lakes/Ohio Valley/Mid-Atlantic. Meanwhile, increasing potential for Pacific energies to work inland in separated or broader southern stream flow are expected to renew some monsoonal connections/convection for the Southwest and South-central Great Basin/Rockies. Meanwhile expect a threat for locally excessive, but less organized thunderstorms/heavy downpours in the hot/humid sector in the southern/eastern U.S. which may align with meso-boundaries and local convergence effects. However, there are also several systems of opportunity for heavy rainfall over Florida and along the Gulf Coast with approach and passage of two deeply moist tropical waves being followed/coordinated by WPC and NHC. Overall, models and ensembles still show above normal forecast spread into the lower 48 manifested mainly from uncertain flow evolutions upstream over the Pacific. This may in part be due to multiple upstream x-tropical system flow entrainments and ripple effects along with uncertain multiple flow stream interactions/separations into North America. This is resulting in ample run to run flip flopping with even ensemble means showing uncharacteristic variance. Accordingly, the WPC medium range product suite was primarily derived from a composite blend of latest ensemble means and NBM/WPC continuity. Although overall late summer pattern details/timings remain unresolved, the main focus regions for heavier organized precipitation are similarily suggested by the bulk of guidance. 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