**Trader sentiment for Mexico City’s July 31 high clusters tightly around 25–27 °C (cumulative ~92 % probability) because official forecasts and historical climatology converge on that narrow range for the city’s high-elevation, rainy-season environment.** Mexico City sits at roughly 2,240 m, where July mean daily maxima normally reach only ~24–25 °C. The current rainy-season pattern brings frequent afternoon convection; cloud cover and showers that develop after midday limit surface heating and keep highs from exceeding the mid-20s. Recent model runs (including Met Office guidance) point to a 26 °C peak on the 31st under partly cloudy skies with isolated showers, while slightly earlier or heavier convection could cap the reading at 25 °C. Conversely, a brief window of stronger insolation before storms arrive could push the thermometer to 27 °C. Because the difference between these outcomes hinges on the precise timing and coverage of afternoon convection—variables that evolve quickly in numerical weather prediction—the market reflects genuine short-term forecast uncertainty rather than divergent long-term trends. No anomalous heat wave or blocking pattern has altered the baseline conditions, keeping the distribution tightly centered on the climatological expectation.