**Forecast models from Météo-France, Met Office, and global ensembles show a pronounced cooldown on September 16 after a hot spell, with daytime highs expected near 21–22°C under partly cloudy skies and light northwest winds.** A frontal passage following the 31–32°C peak on the 15th introduces cooler maritime air, limiting afternoon heating despite mostly dry conditions (rain probability ~10–25%). This aligns with climatological norms of ~21.5°C for mid-September in Paris and explains the market’s tight clustering around 21–23°C. Short-range model runs and official guidance show minimal spread, though minor timing differences in cloud cover or wind could nudge the daily maximum by 1°C. With resolution imminent, the implied probabilities reflect high-confidence trader assessment of these atmospheric shifts rather than long-term variability.