Trader sentiment clusters tightly around 17–20°C for Madrid’s August 21 minimum because official forecasts and ensemble models converge on overnight lows of 18–19°C under stable high pressure and mostly clear skies. Radiative cooling after daytime highs near 30°C is moderated by moderate humidity, light southwesterly winds, and Madrid’s urban heat island, which prevents deeper drops. Small probability spreads among the leading bins reflect minor model differences in wind speed and cloud cover that can shift the exact minimum by 1–2°C, while probabilities collapse below 16°C or above 21°C given the absence of unusual cold advection or strong winds. Updated AEMET and ECMWF guidance through the night will refine these narrow ranges before official recording closes.