Recent model consensus from agencies like INMET and ECMWF points to a moderating cold front and polar air mass arriving around May 18, holding São Paulo’s maximum near 19–21 °C. Subtle differences in frontal timing, cloud cover, and urban heat retention create the tight spread among these outcomes, with 20 °C edging ahead as traders weigh afternoon clearing potential against lingering marine influence from the southeast. Historical May highs average 22–24 °C, so current cooler steering patterns explain the compressed probability distribution; any last-minute delay in the front or stronger subtropical ridge could push readings above 21 °C, while earlier or deeper cooling would favor 19 °C or lower. Updated short-range runs expected within 48 hours will likely sharpen resolution before the market closes.