Forecast models from agencies like the National Meteorological Service of Mexico point to an overnight low near 13–14°C for Mexico City on August 21, driven by the city’s 2,240-meter elevation, which consistently produces cooler nights than sea-level locations at the same latitude. Persistent cloud cover from the ongoing rainy season has limited radiational cooling while recent scattered showers have added moisture that moderates temperature drops. Historical August minima cluster around 12–15°C, with 2026 observations so far falling in the middle of that range. The tight clustering of market-implied odds on 13°C, 14°C, and 15°C reflects remaining uncertainty over exact timing of any late-day convection and differences among official measurement stations. Updated model runs and the day’s final minimum reading will resolve the outcome.