Precipitation is water falling from the sky in any form: rain, snow, sleet, or hail. When weather forecasters predict precipitation, they mean you should expect something wet (or frozen) to fall from the clouds.

The word comes from a scientific understanding of how water moves through our atmosphere. Water evaporates from oceans, lakes, and rivers, rises into the air, forms clouds, and eventually falls back to Earth as precipitation. Whether you experience rain during spring, snow in winter, or hail during a summer thunderstorm, you're experiencing different types of precipitation.

Meteorologists measure precipitation to track weather patterns and predict droughts or floods. A region might receive 40 inches of precipitation per year, meaning that if all the rain and melted snow were collected in a tall container, it would measure 40 inches deep. Deserts receive very little precipitation, while tropical rainforests receive enormous amounts.

Scientists also use precipitate as a verb in chemistry to describe when dissolved substances suddenly form solid particles in a liquid, like when you mix two clear solutions and a cloudy solid appears. This shares the core idea of something falling or separating out, though in chemistry it happens at a microscopic level in a test tube rather than from clouds above.