Trader consensus on an 8°C low for Madrid on October 10 rests on real-time observations from official stations under a stable high-pressure system with clear skies and light northeasterly winds. These conditions promote strong nocturnal radiative cooling after daytime highs near 23–25°C, consistent with model guidance and historical October minima around 11–12°C that have trended cooler amid recent dry patterns. AEMET and airport METAR data through the evening confirm the overnight drop aligning with this threshold. The market-implied odds reflect this convergence of surface measurements and forecast verification. Only an unexpected late cold front, station-specific microclimate variation, or post-hoc data revision could shift the recorded minimum.