Recent forecasts from GFS and other models indicate a high-pressure ridge over northern France will deliver clear to partly cloudy skies and light northeast winds overnight into September 21, favoring radiative cooling and supporting a minimum near 11–12 °C in central Paris. This aligns with the climatological average low of 11 °C for the date and recent observations of 12–13 °C lows under similar anticyclonic conditions. Traders assign the highest probabilities to 10 °C and 11 °C because small differences in boundary-layer moisture, exact wind speed, or urban heat-island effects could shift the overnight low by 1–2 °C, while the 26.5 % chance attached to 9 °C or below reflects the tail risk if clearer skies and drier air enhance cooling beyond current model consensus. No major frontal systems or precipitation are expected to moderate temperatures before dawn.