Traders see closely matched probabilities around 11–15°C for São Paulo’s daily minimum on August 21 because short-term forecast variability and model spread leave the exact overnight low uncertain. In the Southern Hemisphere winter, radiative cooling under clear skies can drop temperatures several degrees below daytime averages of 23–26°C, while any increase in cloud cover, humidity, or light winds limits that drop. Official measurements from urban stations also incorporate the city’s heat-island effect and elevation around 760 m. Recent model runs show only modest cold-air advection, keeping most guidance clustered in the 12–16°C range and preventing any single outcome from dominating the market.