In preparing for Hurricane Irene’s weekend arrival, communities along the East Coast prepared for the worst. New York City Mayor Michael Bloomberg insisted on Friday that New Yorkers “must, I repeat the word ‘must,’ evacuate beginning tomorrow and complete the process by 8pm tomorrow night.” But his historic preparations turned out to be for a less-than-historic storm, at least in New York City. While all Americans are glad that the loss of life, property and infrastructure was relatively minimal, many people are now wondering: why was Irene so much less the threat we were told it would be? Adam Sobel, professor of earth and environmental sciences at Columbia’s School of Engineering and Applied Sciences and at the Lamont-Doherty Earth Observatory, on the complexity of predicting the weather.