Science: Why Rain? Why Snow?

After lo, these many years, most meteorologists remain baffled by a couple of apparently simple questions: "Why does it rain?" and "Why does it snow?"

This much is known: most clouds are made of water droplets so tiny that they behave something like the particles in smoke. They cannot gather into larger drops unless an outside "something" makes them do it. In temperate climates this something is generally the low temperature of high altitudes, which turns some of the droplets to small ice crystals. Since ice has an attraction for water, these droplets grow at the expense of the cloud's smoke-sized...

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