Trader consensus around a 20°C daily maximum in Beijing on September 30 reflects consistent official forecasts and real-time observations showing a cool northwest flow under clear skies suppressing temperatures well below the seasonal climatological average of roughly 24–25°C. Numerical weather models from agencies such as the China Meteorological Administration converged on a peak of 20–22°C during afternoon hours, with surface readings confirming values near 20°C amid low humidity and moderate winds. This outcome aligns with a broader late-September cooling pattern driven by polar air intrusions. A realistic challenge would require either a localized measurement exceeding the threshold at the official station or a rapid model revision from unexpected warm advection, though current conditions and timing near market resolution make such shifts improbable.