Forecast uncertainty around cloud cover and precipitation is the main driver keeping Chengdu's June 21 high-temperature market odds tightly clustered between 25–28 °C. Recent model runs show light rain or thundershowers possible that day due to East Asian monsoon moisture surging into the Sichuan basin, which would suppress daytime heating through reduced insolation and evaporative cooling. Ensemble guidance diverges on timing and intensity of these showers, producing the spread in outcomes traders are pricing. Historical June climatology places average highs near 28–30 °C, but persistent humidity and basin topography amplify sensitivity to even modest rainfall changes. Updated short-range model runs and official China Meteorological Administration guidance expected in the next 24–48 hours could shift implied probabilities if clearer skies emerge.