Dust is also needed to form clouds. As you go higher in the atmosphere, the cooler the temperature gets. Sometimes clouds are formed because moist air is forced upward over mountains. Scientists who study weather are called meteorologists . They look at the temperature, air pressure, winds and clouds and tell us whether to expect rain or cold air.
Meteorologists have names for different kinds of clouds.
These names describe what the cloud looks like and how far above the ground the cloud is. Big fluffy clouds are called cumulus and they can be in any part of the atmosphere. Special cumulus clouds which bring thunderstorms are called cumulonimbus . Cumulonimbus clouds are dark because their bases are low, but their tops can reach high up into the atmosphere. Rain can form in any part of a cumulonimbus cloud.