**Mild high-pressure conditions and light winds are supporting overnight lows in the 17–18°C range for Paris on September 3, aligning with the market’s tightest odds on those outcomes.** Current model guidance (GFS, ECMWF-influenced runs) shows a stable anticyclone with surface pressures near 1022 hPa, light southwesterly to westerly winds of 2–4 m/s, and limited cloud cover overnight. These factors promote moderate radiative cooling after daytime highs of 27–28°C, but the mild maritime air mass and urban heat island effect in central Paris limit further drops. Recent forecasts cluster the daily minimum around 17–19°C, consistent with the 39% and 32.5% probabilities assigned to 17°C and 18°C. Slight model spread arises mainly from variations in low-level cloud or wind speed: clearer, calmer conditions favor the lower end near 15–16°C (29% and 17.5% odds), while any increase in mixing or residual moisture pushes values toward 18–19°C. Historical September 3 averages (≈13°C low) are well below current guidance because of the warmer synoptic pattern this year. Traders are pricing the narrow scientific uncertainty between these scenarios, with resolution hinging on the final observed minimum from official stations. New model updates overnight will provide the next key data point before the market settles.