A cloud occurs when the invisible water vapor in the air becomes visible water droplets or ice crystals. The water vapor becomes visible by cooling. Warm clouds exist at temperatures above the freezing point. Cold clouds exist at or below freezing. Fog is a cloud in touch with the ground.
Water droplets form on articles near the Earth's surface and create fog.
Cumulus are white, puffy, fair weather clouds. Those bubbles rise to the surface of the water just like air heated by the sun rises and cools to form these puffy bubble shapes in the sky. More Information Cumulonimbus are huge cumulus clouds that form towers in the sky and signal a coming storm. Lightning, thunder, and even violent tornadoes sometimes accompany intense cumulonimbus clouds. More Information Stratus are grey clouds that blanket the whole sky.