Cloud formations is a topic often brought up on competitions, as well as being required for the Observation Scoutcraft Badge.
Low Level Clouds
Clouds found below 2000 meters (6500 feet)
Cumulus clouds are found at low altitudes and are often described as looking similar to cauliflower. They are distinctly "puffy", develop on clear, sunny days, are formed in the late morning and disappear in the evening. . They predict fair weather 
Cumulonimbus clouds grow on hot days when warm, wet air rises very high into the sky. From far away, they look like huge mountains or towers , are seen as bringing a thunderstorm with them . The bottom of the cloud is often dark grey to black, whereas the top is whiter 
Stratocumulus clouds resemble a blanket of cotton (although they can also be spread out ): they're bigger than cumulus clouds and have a flat bottom with a ragged top. They generally predict fair weather in the short term, but possible bad weather in the future .
Clouds found between 2000 meters and 7000 meters (6000 and 25000 feet)
Altostratus clouds are gray or blue-gray mid-level clouds composed of ice crystals and water droplets. The clouds usually cover the entire sky . Generally the sky is not visible and the sun is considerably dimmed . This generally means that there will be continuous rain or snow.
Nimbostratus clouds form a dark-grey, thick layer across the sky, usually thick enough to block out the sun. They signal the arrival of slow but steady precipitation (rain or snow) .
Clouds found between 5000 meters and 14000 meters (16500 and 45000 feet).
Cirrus clouds seem delicate and whispy. This shape is given to them by various wind currents . They generally occur during fair or good weather and indicate the arrival of a warm front or a storm .