**Recent developments show Sao Paulo experienced cooler-than-average overnight conditions on September 13, 2026, driven by persistent cloud cover, light rain, and southeasterly winds that limited radiative cooling.** Official monitoring data and model outputs indicated minimum temperatures clustered near 11–15 °C, with hourly readings from Congonhas and other stations bottoming out around 11–12 °C amid high humidity (90 %+ ) and overcast skies. This setup reduced the typical nocturnal temperature drop compared with clearer nights, while urban heat-island effects and measurement timing at different stations introduced small variances. Traders priced the close contest among 13 °C, 14 °C, 15 °C, and 10 °C-or-below outcomes because ensemble forecasts diverged on the precise low, reflecting uncertainty in boundary-layer moisture and wind mixing. The market-implied odds therefore aggregate real-capital assessments of these meteorological variables rather than a single deterministic value.