Clouds are visible masses of condensed water vapor or ice crystals suspended in the atmosphere. Understanding their classification is crucial for comprehending weather patterns and climate. This module explores the fundamental classification system based on altitude and appearance.

Clouds are primarily classified based on two main criteria: their altitude in the atmosphere and their appearance (shape and texture). This system, largely developed by Luke Howard in the early 19th century, categorizes clouds into ten basic genera.

Clouds are grouped into three main altitude categories: high, middle, and low. These categories are defined by the typical height range where these clouds form, though their exact altitudes can vary with latitude and season.

Beyond altitude, clouds are described by their form. The primary forms are 'cirrus' (wispy), 'cumulus' (puffy), 'stratus' (layered), and 'nimbus' (rain-bearing).

Let's explore the most common cloud types within these categories:

Composed entirely of ice crystals, these clouds are thin and wispy.

<strong>Cirrus (Ci):</strong> Detached, delicate, fibrous, or feathery clouds. Often indicate fair weather but can precede a change.

<strong>Cirrocumulus (Cc):</strong> Thin, white patches, sheets, or layers of clouds without shading, composed of very small elements in the form of grains or ripples. Often called 'mackerel sky'.

<strong>Cirrostratus (Cs):</strong> Transparent, whitish cloud veil of fibrous or smooth appearance, totally or partly covering the sky, and generally producing halo phenomena.

These clouds can be composed of water droplets, ice crystals, or a mixture.

<strong>Altocumulus (Ac):</strong> White or greyish patches, sheets, or layers of clouds, generally with shading, composed of laminae, rounded masses, rolls, etc., which are sometimes partly fibrous or diffuse.

<strong>Altostratus (As):</strong> Greyish or bluish sheet or layer of clouds of fibrous or uniform appearance, totally or partly covering the sky, and having in the thicker parts the appearance of a more or less uniform mass.

These clouds are typically composed of water droplets and are found close to the ground.

<strong>Stratus (St):</strong> Generally grey cloud layer with a fairly uniform base, which may give drizzle, ice prisms or snow grains. When the sun is visible through the cloud, its outline is clearly discernible.

<strong>Stratocumulus (Sc):</strong> Grey or whitish patches, sheets or layers of clouds which almost always have dark parts, composed of tessellations, rounded masses, rolls, etc., which are not fibrous.

<strong>Nimbostratus (Ns):</strong> Grey cloud layer, often dark, the base of which is diffuse and continuously raining or snowing. It is thick enough throughout to blot out the sun.

These clouds span multiple altitude levels and are often associated with significant weather.

<strong>Cumulus (Cu):</strong> Detached clouds, generally dense and with sharp outlines, developing vertically in the form of rising mounds, domes or towers, of which the bulging upper part often resembles a cauliflower. The sunlit parts are mostly brilliant white; their base is relatively dark and horizontal.

<strong>Cumulonimbus (Cb):</strong> Heavy and dense cloud, with considerable vertical extent, in the form of a mountain or huge towers. At least part of its upper portion is usually smooth, fibrous or striated, and nearly always flattened; this part often spreads out in the shape of an anvil or vast plume.

The ten principal cloud genera are: Cirrus (Ci), Cirrocumulus (Cc), Cirrostratus (Cs), Altocumulus (Ac), Altostratus (As), Nimbostratus (Ns), Stratocumulus (Sc), Stratus (St), Cumulus (Cu), and Cumulonimbus (Cb). Understanding their formation, altitude, and appearance is key to interpreting weather maps and forecasts.