The primary driver behind the tightly clustered market-implied odds favoring a 21–24 °C minimum in Chongqing on August 29 is the strong rainfall episode and associated cold-air advection that began overnight on August 28. Official forecasts from the Chongqing Meteorological Bureau highlighted 30–80 mm (locally >100 mm) of rain, 6–9 grade gusts, and a sharp drop in daytime highs to 26–31 °C in central districts, with overnight temperatures falling into the low-20s °C range as cloud cover, evaporative cooling, and northerly flow suppressed the typical August nocturnal minimum near 25–26 °C. Traders are differentiating the narrow band of leading outcomes by weighing subtle differences in rain timing, model consensus on boundary-layer mixing, and potential urban heat-island effects at official observation sites, while the sub-20 °C tail reflects residual uncertainty about localized cooling pockets and the above-25 °C outcomes price in any slower clearing. Resolution hinges on the final 24-hour minimum reported by the China Meteorological Administration.