Trader consensus on Polymarket closely splits between 29°C (30%) and 30°C (30%) for São Paulo's highest temperature on April 17, reflecting numerical weather prediction models like GFS and ECMWF projecting daytime peaks around 29°C amid a subtropical high-pressure ridge promoting clear skies and solar heating. Recent observations show April temperatures running +1.5°C above the 21°C monthly normal per INMET data, with a warming trend from scattered clouds on April 15 (forecast 27°C) to mostly sunny conditions by the 17th. Differentiating factors include afternoon cloud development timing—early shading could cap at 29°C via reduced insolation, while delayed onset or urban heat island amplification might push to 30°C. INMET updates and fresh model ensembles on April 16 will likely sharpen this uncertainty.