Extended Forecast Discussion NWS Weather Prediction Center College Park MD 246 AM EDT Tue Aug 28 2018 Valid 12Z Fri Aug 31 2018 - 12Z Tue Sep 04 2018 ...Guidance/Predictability Assessment and Weather Highlights/Hazards... It remains the case that a series of shortwave troughs of uncertain amplitude will dig over the northeastern Pacific and split off the West Coast, with more energetic flow and modest precipitation potential across the northwestern U.S. to then progress east-northeastward through southern Canada and the U.S. northern tier. Wavy frontal systems underneath will combine with deepened moisture and instability to fuel periods of heavy convection, focused from the eastern Plains/Mississippi Valley to the Great Lakes/Ohio Valley/Mid-Atlantic. Meanwhile, increasing potential for Pacific energy to work inland in separated or broader southern stream flow next weekend/early next week may renew monsoonal connections over 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. There is also potential for heavy rainfall over Florida and along the Gulf Coast as per WPC/NHC coordinated tropical wave passage. Overall, models and ensembles show above average forecast spread into the lower 48 manifested mainly from uncertain flow evolutions upstream over the Pacific. This may in part be due to upstream tropical system flow entrainments and associated ripple effects. This is resulting in ample run to run flip flopping with even ensemble means showing uncharacteristic variance. The WPC medium range product suite used a composite solution. 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