Diverging numerical weather prediction models create near-even market-implied odds between a minimum of 12°C or below and 22°C or higher in São Paulo on October 4. Recent cold air advection and patchy cloud cover have produced overnight lows near 12–17°C in early October, with radiative cooling enhanced under clearer skies but moderated by increasing northerly winds and humidity. Ensemble spreads highlight uncertainty in exact timing of any frontal boundary and boundary-layer mixing, while official guidance from sources like the Met Office and ECMWF shows projected overnight minima ranging 13–20°C. Updated high-resolution runs and satellite observations ahead of October 3–4 will likely refine the temperature trajectory and shift trader positioning.