Anyone who's gone outside and looked at the sky has, without doubt, seen more than a few clouds in their day. Ever-present in many parts of the world and perhaps a bit too prevalent for some tastes, clouds are just another aspect of life. A neat, sometimes inexplicable and awe-inspiring aspect, but something that won't cause much of a fuss among the average person... unless they start pouring down rain, of course.
Yet anyone who pays more than a token amount of attention to clouds will notice that they come in a variety of different forms. Some are little more than wispy streaks; others are thick, uniform blankets; yet others massive, heaped, vertical creatures that look heavenly on top and... less so on the bottom. Indeed, clouds are surprisingly diverse in their types, and the formation and definition of these clouds is typically determined with their elevation in the troposphere.
This article is concentrated on low clouds, a form of clouds whose bases run from ground level (fog) to roughly 6,500 feet, whereupon they are defined as middle clouds instead. They come in the following four varieties:
- Stratocumulus clouds are small, low-flying clouds that typically look rather gray and lumpy. Each cloud is relatively small, though they're densely packed together. Despite their gray coloring stratocumulus clouds typically carry only token amounts of precipitation and won't result in any major storms, though they may serve as precursors to more volatile clouds.
- Stratus clouds are, like stratocumulus clouds, often sky-obscuring and appear in dense formations. Unlike stratocumulus clouds, however, stratus formations come in thick, seemingly unbroken gray bands across the sky. They will also bring fairly mundane amounts of precipitation and contribute to typical 'gray' days. Stratus clouds will appear as fog if they develop low enough on the land.
- Cumulus clouds jump away from the other two types in that they can come in large clusters or floating on their own or in small concentrations. They're characterized by gray bases and pronounced peaks stretching vertically into the sky. Cumulus clouds can herald poor weather to come or become volatile on their own.
- And, when they become volatile, cumulus clouds develop into cumulonimbus clouds. These massive formations typically stretch high into the atmosphere, creating a classic anvil head shape, and usually herald incoming storms or, in particularly harsh cases, supercells. Cumulonimbus clouds typically have dark clouds at their bases and white clouds closer to the top, the precipitation in the cloud gathering primarily at the bottom of the cluster. If you see a cumulonimbus cloud then it's best to get inside in a hurry.
It can be a little difficult to classify certain clouds as certain varieties at first because they come in different shapes and sizes each day, though with a bit of practice picking them out from one another isn't too difficult. Watch how they blanket the sky and compare what you see to pictures online and what you've seen in previous days. Note, too, that there are more divisions into which you can separate these clouds, though doing so is getting more specific than the average cloud admirer will care to do.
Lloyd, Julie. A Pocket Guide to Weather. Parragon Books, 2007.