Recent National Weather Service and NOAA forecasts highlight moisture advection and afternoon instability as the main drivers for scattered showers and thunderstorms on September 15, particularly across the Southeast and parts of the Midwest where PoPs reach 60-80% in areas like Florida and the Great Lakes region. Drier high pressure supports mostly sunny conditions and near-zero precipitation chances in the Northeast and much of the West, consistent with climatological late-summer patterns. Model consensus shows typical convective uncertainty at this range, with steering flows and local boundaries determining exact coverage; traders should watch the next NWS short-range updates and evening model runs for shifts in instability or frontal positioning that could alter resolution criteria for specific locations.