Forecast models from multiple agencies align on a high of 18–20°C for Buenos Aires on September 30, driven by post-frontal clearing under southwesterly flow after earlier rain, with mostly sunny skies and light winds limiting further cooling or warming. This setup favors the market's leading 19°C and 20°C outcomes as typical late-September maxima once daytime heating peaks under stable conditions, consistent with regional climatology showing average highs near 18°C. Minor model spread in exact timing of peak temperatures and boundary-layer mixing creates the observed distribution favoring 18–20°C while keeping lower or higher extremes below 5% probability. Official Servicio Meteorológico Nacional observations at key stations will resolve the market.