Forecast uncertainty across numerical weather models drives the tight clustering of market-implied odds around 9–12°C for São Paulo’s minimum temperature on August 22. Ensemble spreads from global and regional systems reflect variable cold-air advection from the south, differences in nocturnal radiative cooling under partly cloudy skies, and boundary-layer mixing influenced by light winds. Urban heat-island effects in the metropolitan area can raise observed minima by 1–2°C relative to rural stations, while model resolution of local topography adds further variance. Historical August climatology places typical lows near 11–13°C, so traders weigh any incoming frontal passage against the chance of clearer, calmer conditions that favor deeper cooling. Updated model runs and official observations tomorrow morning will determine resolution.