When the warm valley air traveled up to a mountaintop's cooler air, the weather was going to change quickly. This heavy monsoon type of downpour happened regularly in the mile-high altitude of Mexico City. Our lodgings had a rooftop terrace for cooling off, but this storm was amazing for arching clouds that mimicked the city skyline! I was glad someone had a top floor light on because it showed the contrast from black to a very little amount of white!