by David Murphy
There are three basic cloud types. Cirrus clouds are the highest from the surface, and usually appear white and thin. They often look like a veil and sometimes have wispy curves. Some cirrus clouds are described as mare's tails, because they look like a horse's tail flowing through the otherwise blue sky. The reason for the swirling pattern common in cirrus clouds is the strong high-level wind currents which interact with the clouds as they form. Cirrus clouds form in cold, relatively dry air. They are generally made-up of ice crystals.
Cumulus clouds are the fluffy, billowing clouds that appear both on dry, pleasant days as well as rainy days. I often refer to these as mashed potato clouds when I'm describing them to children. Cumulus clouds typically have flat bottoms, but globular, puffy bodies that rise from low altitudes to levels well above the surface. Cumulus clouds sometimes dot the sky on bright days when no rain is forecast. In this case, they are referred to as fair weather cumulus. But this same type of cloud also forms major rain clouds, when conditions are right. In this case, they are commonly called rain clouds, or even thunderstorms (once they begin producing thunder and lightning). Thunderstorms, (or clouds of vertical development which lead to thunderstorms) feature the largest, most moisture-laden of all cumulus clouds.
Finally, Stratus clouds form broad, level sheets of cloud cover above the surface, sometimes relatively low in altitude. Stratus clouds are associated with light rain and drizzle, and often greet you on days when prolonged overcast, damp conditions are in the forecast.