Extended Forecast Discussion NWS Weather Prediction Center College Park MD 150 AM EDT Sun Aug 26 2018 Valid 12Z Wed Aug 29 2018 - 12Z Sun Sep 02 2018 ...Weather Pattern Highlights and Hazards... A series of shortwave troughs will dig over the northeast Pacific to split off the west coast, with energetic flow and modest precipitation potential working into the Pacific Northwest/West before progressing east-northeastward over southern Canada/U.S. northern tier. Wavy frontal systems underneath will pool deepened moisture and instability to fuel periods of heavy convection/complexes, with a main medium range focus from the eastern Plains/Mississippi Valley to the Midwest/Mid-South and Northeast/Mid-Atlantic. Expect a threat for locally excessive, but less organized thunderstorms/heavy downpours into a hot sector sprawling the southern/eastern U.S. to align with meso-boundaries and local convergence effects. This potent late summer hot sector under ridging aloft will offer spotty record maximum temperatures over the Northeast/Mid-Atlantic Wednesday with numerous record high minimum temperatures mainly Wednesday into Thursday with pooling deep moisture ahead of a subsequently moderating eastern U.S. frontal push. Otherwise, the hot sector over the U.S. southern tier generally holds firm for the coming week. ...Guidance and Uncertainty Assessment... The larger scale flow pattern is reasonably well depicted in guidance so while overall weather threats seem documented, deterministic efforts to detail much less predictable embedded features and local focus for convection are increasingly suffering from run to run variance and flip-flopping. Accordingly, the WPC medium range product suite was mainly derived from a composite blend of ensembles, the National Blend of Models and WPC continuity, with less than normal determinitsic model input amid grown uncertainty. 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