How Wind and Clouds Form

Have you ever felt the wind on your face and wondered what it is? Wind is moving air — and air moves because of differences in temperature. Clouds form because of the same water cycle we learned about in Lesson 11.

How wind forms

• The sun heats the ground. The ground warms the air above it.
• Warm air is lighter than cool air, so it rises upward.
• Cooler, heavier air from nearby rushes in to fill the gap — that rushing movement is wind.
• The bigger the temperature difference, the stronger the wind.

Three types of clouds

• Cumulus — big, puffy, white clouds that look like cotton balls. They appear on fair, sunny days and float at a medium height.
• Stratus — flat, gray sheets of cloud that cover the whole sky in a blanket. They bring dull, drizzly weather.
• Cirrus — thin, wispy streaks that sit very high up, made of ice crystals. They often mean a change in weather is coming.

How clouds form

• Warm, moist air rises and cools down high in the sky.
• Water vapor condenses onto tiny dust particles, forming billions of water droplets.
• Enough droplets grouped together become a visible cloud.