Why does the wind blow? What does air pressure have to do with a thunderstorm? Why is a mountaintop snowy while the valley below is warm? The answers to these questions all involve the layer of air surrounding Earth—the atmosphere. Earth’s atmosphere is always in motion. It moves clouds, storms, and warm and cold air from one part of the planet to another. In this fact-packed book, discover how the ever-changing atmosphere determines weather around the globe.