1. Guided Notes on Moisture in the Atmosphere Chapter 11, Section 3

2. 1. Clouds form when warm, moist air rises, expands, and cools in a convection current.

3. 2. When air reaches the dew point, water vapor condenses around condensation nuclei, which are small particles in the atmosphere around which cloud droplets form. Examples of condensation nuclei are sea salt and dust. When millions of droplets collect, a cloud forms.

4. 3. Clouds also form through orographic lifting, which is when wind encounters a mountain and the air has no place to go but up.

5. 4. Sometimes clouds form when two air masses of differing temperatures collide. As warm air moves into an area of cool air, the bulk of it will be forced to rise over the more-dense, cold air. As warm air rises and cools, the water vapor in it condenses and forms a cloud.

6. 5. Air can become unstable if it is cooler than the surface beneath it. If temperature conditions are right and the air mass rises rapidly, it can produce the types of clouds associated with thunderstorms.

7. 6. As water vapor in the air condenses, heat is released. This heat warms the air. This latent heat can provide energy to a weather system, thereby increasing its intensity.

8. 7. When cloud droplets collide, they join together to form a larger droplet in a process called coalescence. Eventually the droplet becomes too heavy to be held aloft and the droplet falls to Earth as precipitation.

9. 8. Examples of precipitation include rain, snow, sleet, and hail.