Recent cooling from Atlantic maritime air and increased cloud cover ahead of showers are the main drivers setting Paris overnight lows near 17–19°C on August 19, consistent with the tight market clustering. Model consensus shows a frontal passage moderating temperatures after earlier heat, with radiative cooling limited by clouds yet still allowing minima in the upper teens depending on exact timing of clearing and wind. Ensemble spreads in boundary-layer mixing and precipitation timing create the differentiation between 18°C and 19°C outcomes versus slightly lower 17°C scenarios, while official guidance from Météo-France and numerical weather prediction runs emphasize this narrow range rather than extremes. Traders’ skin-in-the-game consensus thus reflects genuine short-term forecast uncertainty in a rapidly evolving synoptic pattern.