Trader consensus around 11–15°C for São Paulo’s overnight minimum on August 21 reflects typical mid-winter conditions in the subtropical climate, where average lows hover near 13–15°C. Primary drivers include the strength of any polar air advection from the south, extent of clear skies promoting radiative cooling at the surface, and local wind speeds that limit or enhance mixing. Subtle forecast differences in model runs—such as timing of a weak trough or variations in boundary-layer moisture—separate the tightly clustered outcomes, while the very low probabilities below 10°C or above 16°C align with historical rarity of stronger cold fronts or anomalous warming this time of year. Official station data and updated guidance from meteorological agencies will resolve the market.