Lost in the Clouds

September 2011 Prof. Scarlet Leslie

Eagles soar with grace, but they aren't the only wonderful thing in the skies. There is the sun, moon, stars, rainbows, and clouds. Yes, clouds!

What is a cloud? Well, not exactly white, fluffy cotton candy in the sky, that's for sure! Depending on the height of the cloud, it is composed of water droplets or ice crystals. As the air becomes saturated with water vapor, the water vapor gas condenses to liquid water droplets that are visible as clouds. A cooler temperature also favors cloud formation, which is why clouds form so high up in the atmosphere. Eventually, precipitation falls from the cloud, usually as rain and snow.

There are three main types of clouds - cirrus, cumulus, and stratus.

Cirrus clouds are typically the highest clouds, forming at altitudes higher than 5,000 m (16,500 ft). They can be white to faint grey. Cirrus clouds are thin and wispy, often described as tufts. They are commonly called mare's tails. Cirrus is Latin for curly, since cirrus clouds can look like curly hair. Although cirrus clouds are seen on days with almost clear blue skies, they are actually a warning that severe weather will arrive in a few days. Cirrus clouds show up before tropical cyclones and weather fronts.

Cumulus clouds are the puffy clouds everyone is used to seeing. In Latin, cumulus means heap or pile. They have a base below 2,000 m (6,500 ft), but grow vertically. Cumulus clouds can be lone or in lines or in groups. Cumulus clouds are the precursor to the dreaded anvil-shaped cumulonimbus clouds. Cumulonimbus clouds almost always bring rain, since nimbus means rain. They also bring thunder and lightning, possibly even tornadoes. The towering cumulonimbus also provide a perfect turbulent environment for the formation of hail.

Stratus clouds are seen below 2,000 m (6,500 ft). They form horizontal layers. A cloudy day is usually due to stratus clouds blocking the sun. Fog is sometimes a really low stratus cloud. The precipitation from stratus clouds is usually light snow or drizzle.

Many clouds are actually a combination of these three main types. Clouds at high altitudes have cirrus or the prefix cirro- in their names, like cirrostratus and cirrocumulus. The middle clouds are altocumulus or altostratus. Stratocumulus and nimbostratus are types of low clouds.

An old saying at sea is, "Mackerel scales and mare's tails make lofty ships carry low sails." Mackerel scales are the altocumulus clouds that look like fish scales. Mare's tails are cirrus clouds mentioned earlier. Sailors knew they had to lower the sails of their ships to prepare for incoming storms when they spotted those clouds in the sky.

Cloud watching is not only for weather warnings. Find a patch of grass to lie on any nice day and watch as that fluffy... elephant? No, hippocampus!... floats by. Don't be afraid to get lost in those cumulus clouds, at least until they become cumulonimbus clouds.