The weather is the set of all extant phenomena in a given atmosphere at a given time. The term usually refers to the activity of these phenomena over short periods (hours or days), as opposed to the term climate, which refers to the average atmospheric conditions over longer periods of time. When used without qualification, "weather" is understood to be the weather of Earth.
A cloud is a visible mass of condensed droplets or frozen crystals suspended in the atmosphere above the surface of the Earth or another planetary body. The branch of meteorology in which clouds are studied is nephology.
The color of a cloud tells much about what is going on inside the cloud. Clouds form when relatively warm air containing water vapor is lighter than its surrounding air and this causes it to rise. As it rises it cools and the vapor condenses out of the air as micro-droplets. These tiny particles of water are relatively densely packed, and sunlight cannot penetrate far into the cloud before it is reflected out, giving a cloud its characteristic white color.
