Traders assign nearly identical 49% implied probabilities to a minimum of 16°C or below versus 26°C or higher in São Paulo on October 11 because short-range ensemble forecasts exhibit substantial spread in the timing and intensity of an approaching cold front. Numerical weather prediction models diverge on whether a surge of polar air will arrive in time to drop overnight lows sharply or whether persistent subtropical flow will hold temperatures closer to seasonal norms around 20–24°C. Key variables include upper-level trough positioning, Atlantic moisture transport, and boundary-layer mixing, with updated runs from Brazilian and global centers expected to narrow the range before the market resolves.