EYE ON THE SKY

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Each nation had their own system of naming clouds until Luke Howard, a London apothecary, proposed a more coherent classi fication in 1802. He used Latin names to come up with basic cloud types that are still used today.

Clouds are catego rized according to their altitude and shape. The name Cirrus ("lock of hair" in Latin) describes clouds that occur be tween 16,000 and 50,000 feet. Water freezes at that altitude, so cirrus clouds are actually ice crystals, most often appearing as delicate wisps. Middle-level clouds - those which occupy altitudes from 6,000 to 16,000 feet are called Alto. Those below 6,000 feet do not have a blanket name. These three categories are subdivided into cloud shapes. Stratus ("layer" in Latin) are flat, featureless clouds that blanket the sky, regardless of altitude. Cumulus ("heap" or "pile") are the puffy, mashed potato-like clouds we are most accustomed to appreciating on a beautiful day. Clouds which bring rain - again regardless of altitude - are referred to as nimbus ("shower"). That's it. That is all the vocabulary necessary for being a cloud expert. The complexity arises when different types appear together, or when one takes on the characteristics of two or more different types. Even so, we can whittle cloud types down to a basic nine:

CIRRUS (HIGH CLOUDS)
Cirrus
Cirrocumulus
Cirrostratus
ALTO (MIDDLE-LEVEL CLOUDS)
Altocumulus
Altostratus
LOW CLOUDS
Cumulus
Stratocumulus
Nimbostratus
Stratus

Given the Latin we already have under our belts, you could guess with unfailing accuracy what the nine types mean. Of course, lifelong cloud enthusiasts found it necessary to subcategorize the nine into an intimidating array of categories using such names as cirrus densus, cirrus cirrocumulogeitus and cumulonimbogenitus. Forget about them. There is, however, one more type of cloud, unique and uniquely dangerous, that isn't among the nine but merits some attention. The cumulonimbus is the Zeus of the cloud kingdom. This anvil-shaped thunderhead, which can extend in one gigantic chimney of rising hot air from close to the Earth's surface to altitudes of 20,000 to 70,000 feet and more, is the bearer of high winds (including tornadoes), lightning, hail, heavy rains, and numerous hazards to both air and ground traffic. Because it is unmistakable, it rightfully deserves its own category.

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