People have looked at the sky for centuries, both to enjoy its beauty and to evaluate the weather. Clouds are one of the things they study. Clouds are classified by their height, appearance, and origin. They are often the result of weather patterns or topography.
One classification is based on height. High clouds are those that occur more than 20,000 feet above the earth. Middle level clouds occur between 7,000 and 20,000 feet. Low level clouds occur below 7,000 feet.
Clouds are also described by Latin names that refer to their appearance. There are four basic cloud descriptions: cumulus (looking like a heap or pile), stratus (meaning to spread out), cirrus (a curl or curly), and nimbus (referring to rain).
When we put these descriptors together, we get the various types of clouds we see each day.
Cirrus clouds are thin, wispy clouds that often have curled ends. They are high altitude clouds and consist mostly of ice crystals. These are the clouds that take on magnificent colors when the sun is near the horizon.
Cirrostratus clouds are irregular sheets of cloud that cover the sky, but often sunlight or moonlight is just visible through a point in the clouds. These are also high altitude clouds full of ice crystals.
Altocumulus (the “alto” refers to mid-level) clouds appear as bands or rounded lumps like cotton balls. These clouds can contain both ice and water droplets, and when they are in the sky early on a warm day, it may mean thunderstorms will follow by afternoon.
Cumulus are puffy low-level clouds with vertical height. These are the clouds we are watching when we imagine animals and people in the sky.
Stratus are the clouds that occur at the lowest level. When we speak of an overcast day, we are probably referring to a layer of stratus clouds. When a stratus cloud reaches the ground, we call it fog.
Multi-level clouds produce the most precipitation. Nimbostratus (from the words meaning “rain” and “spread out”) can reach from low-level well up into the mid-level. They usually appear dark and produce continuous steady precipitation.
Cumulonimbus are the clouds that produce heavy storms. They develop vertically and can reach into all three levels of the cloud range. They can occur as one huge tower of cloud or form together in a row that is referred to as a squall line. They often have an anvil-shaped top, which is caused by winds at high altitudes that shear off the top of the cloud. Cumulonimbus are associated with frequent lightning, thunder, strong winds, and heavy rain and can produce hail and tornadoes.
Orographic clouds are caused by the interaction of air with the earth’s terrain, most often mountains. These include cap clouds, which sit atop a mountain summit, and lenticular clouds, which are caused by the swift movement of air over rough ground. Lenticular clouds are flat and round and can stack up, one on top of another.
Meteorologists further classify clouds into even more specific categories, but these are the basics. Now, when you look up at the sky, you can name the clouds you see there. Or maybe you’ll still prefer Joni Mitchell’s view and see “bows and flows of angel hair, and ice cream castles in the air.”
