**Cloud cover, precipitation, and radiative cooling under Mexico City's high-altitude rainy-season regime primarily shaped trader views on the September 6 low.** Official forecasts from the Servicio Meteorológico Nacional highlighted afternoon thunderstorms and persistent cloudiness, which limited nighttime heat loss and supported minimums near 12–15 °C. Models converged on roughly 13–14 °C, yet uncertainty over exact rainfall timing, wind speeds, and urban heat-island effects kept probabilities tightly split between 14 °C (50.5 %) and lower thresholds (49.5 %). Clearer intervals could have allowed stronger cooling toward single digits, while widespread rain and humidity maintained warmer readings. With resolution imminent, fresh observational data from surface stations will clarify whether conditions matched the higher or lower cluster of market-implied odds.