Mexico City, at an elevation of 2,250 meters, maintains a mild subtropical climate with relatively stable temperatures throughout the year. April represents late spring in the Northern Hemisphere, when daytime highs in Mexico City typically range from 25°C to 30°C, depending on atmospheric conditions and rainfall frequency. For the high temperature to reach 18°C or below would be anomalous for April in the city, requiring unusual weather patterns such as a strong cold front or persistent cloud cover with sustained rain. The market's 0% YES odds reflect widespread trader confidence that such a temperature decline is extremely unlikely based on historical April patterns and current meteorological expectations. Daily maximum temperatures in Mexico City are objectively measurable and verifiable through multiple official weather stations, ensuring clear market resolution. The odds trajectory typically tightens as April 19 approaches and actual meteorological forecasts become more precise, though the current consensus heavily favors temperatures well above 18°C. This market serves as a straightforward test of short-term temperature prediction accuracy in a stable, well-documented urban climate.