**Forecast models currently point to a low of 21–23°C in Chengdu on September 4, 2026, creating the tight clustering of market probabilities around 21°C and 22°C.** Official guidance from the Chengdu Meteorological Observatory and numerical weather prediction outputs describe a transition from clear conditions under a strong high-pressure system to increasing cloud cover, with light winds and minimal precipitation expected overnight. This setup favors radiative cooling that is moderated by humidity and partial cloudiness, producing minimum temperatures in the low-20s Celsius range. Historical September climatology for the city shows average lows near 20–22°C, so the current pattern aligns with seasonal norms rather than an extreme. The near-even split between 21°C and 22°C outcomes reflects genuine forecast uncertainty typical at this lead time: small differences in cloud timing, boundary-layer mixing, or local urban heat-island effects can shift the overnight minimum by 1°C. Traders appear to be weighting the consensus of regional models and official briefings, which show no strong signals for either a sharper cool-down or warmer advection that would push the low outside the 20–23°C window. Upcoming model runs and the next official forecast update will likely resolve the narrow gap between the leading outcomes.