Forecast models for São Paulo on June 23, 2026, cluster around a daily maximum of 21–23 °C because the city sits under a cool winter airmass typical of the Southern Hemisphere dry season, with limited solar heating from partial cloud cover and possible weak frontal passages. Small differences among leading outcomes hinge on precise timing of any cold-air advection from the south, variations in low-level wind direction that either enhance or suppress urban heat-island effects, and model spread in predicted cloud thickness and boundary-layer mixing. ECMWF and GFS runs show modest disagreement on whether a brief clearing will allow an extra degree of afternoon warming or whether lingering moisture keeps readings closer to 21 °C. Traders weigh these uncertainties against historical June maxima near 22–25 °C, producing the tight distribution seen in current market prices.