Cloud

From Scratchpad

A cloud is the result of the condensation of water vapor in the air.

[edit] Formation of clouds

Water either evaporates or boils into a gas form, called water vapor. The water vapor rises either because it is warmed by the sun or because it reaches an obstacle that forces it to rise. But as it rises, it starts to hit cold air. Once the temperature drops below the air's saturation point, the vapor condenses into a cloud.

[edit] How seasons affect clouds

Winter doesn't have many clouds. The coldness of winter reduces the potential for evaporation. Spring and summer are warmer seasons, so evaporation takes place more frequently. And since it is always cold at cloud level, many clouds form. Autumn is when it gets cold, so the number of clouds in the sky decrease.