Forecast uncertainty across global and regional models is the main driver behind the balanced market odds for Mexico City’s September 28 overnight low. At roughly 2,240 meters elevation, radiational cooling under clear skies can produce lows near 12–13 °C, while increased cloud cover or light rain—common in the waning rainy season—keeps readings closer to 15–16 °C by limiting heat loss. Current runs show a spread from about 12 °C (GEM) to 16–17 °C (some GFS/ECMWF solutions), with precipitation chances of 40–75 % adding further variability. Historical September averages hover near 13–14 °C, but short-term steering patterns and timing of any showers will determine whether the final minimum falls into the cooler or milder cluster that traders currently price nearly equally.