Clouds are a result of condensation process. All clouds are not the same. Clouds continuously change as they drift across the sky. It is interesting to note that every type of cloud has got a descriptive name. The credit goes to a London Pharmacist Luke Howard who introduced the names of three basic groups. Various combinations of these basic terms were used to name the different clouds.
High clouds or the clouds above 20,000 feet are made of ice crystals while low clouds or the clouds below 7000 feet are made of water droplets. Middle clouds or those between 7000-20,000 feet can be made of both water droplets and ice crystals.
The three basic classifications are cirrus, cumulus and stratus. Cirrus clouds are high clouds composed mainly of ice crystals forming thin, transparent veils across the sky. They generally mean pleasant weather. The puffed up cottony clouds that resembles a heap are cumulus. Cumulus clouds are the low or middle clouds. Stratus refers to the low clouds in sheets or layers spread out.
There are two other words ‘alto’ (meaning high) and ‘nimbus’ referring to clouds which bring rain are also used along with the basic classification and give about 10 types of clouds. For instance, altocumulus clouds are patches of small puffed up middle clouds. Similarly Nimbostratus clouds are low clouds that are dark, gloomy rain clouds and bring about light to moderate rainfall. Cirrostratus form thin, wispy layer high in the sky. They are so thin that sun and moon can be seen through them. When cumulus clouds continue to grow vertically they form cumulonimbus clouds which bring thunderstorms. Thus, identification of the types of clouds helps in forecasting rain and thunderstorms.