The approaching cold front is the dominant factor shaping market-implied odds for São Paulo’s September 5 maximum temperature, with 22°C and 23°C each near 26% as traders weigh model consensus on its timing and intensity. Official and ensemble forecasts indicate the front will increase cloud cover and trigger scattered showers or thunderstorms during daytime hours, limiting solar heating and capping highs well below the 27–31°C readings seen on September 3–4. Polar air advection behind the boundary is expected to further suppress afternoon temperatures into the low-to-mid 20s Celsius, consistent with historical September transitions when similar fronts arrive. Key variables still in flux include exact precipitation timing, which could enhance cooling if widespread, and any brief clearing that might allow brief warming toward 24°C. Updated National Meteorological Service and global model runs expected overnight will likely narrow the 21–24°C cluster that accounts for most probability mass.