Clouds

            The first widely accepted system for cloud classification was devised by English naturalist Luke Howard in 1803. It divided clouds into four basic categories:

1.    Cirrus—thin, wispy clouds of ice

2.    Stratus—layered clouds

3.    Cumulus—clouds having vertical development

4.    Nimbus—rain-producing clouds

Generalized Cloud Chart:

Our current classification scheme is a modified version of Howard’s, retaining his four categories and also allows new combinations. The ten principle types of clouds that result are then grouped according to their height and form:

High Clouds (greater than 19,000 ft)	Cirrus (Ci)	Thin, white, wispy clouds of ice resembling mares’ tails.
	Cirrostratus (Cs)	Extensive, shallow clouds somewhat transparent to sunlight, producing a halo around the Sun or Moon.
	Cirrocumulus (Cc)	High, layered cloud with billows or parallel rolls.
Middle Clouds (6,000 ft to 19,000 ft)	Altostratus (As)	Extensive, watery, layer clouds composed of water droplets. Allows some penetration of sunlight but Moon or Sun appears as bright spot within cloud.
	Altocumulus (Ac)	Shallow, mid-level cloud containing patches or rolls, often arranged in bands. Generally more opaque and having less distinct margins than cirrocumulus.
Low Clouds (below 6,000 ft)	Stratus (St)	Uniform layer of low cloud ranging from whitish to gray.
	Nimbostratus (Ns)	Low cloud producing light precipitation. Produces darker skies than altostratus.
	Stratocumulus (Sc)	Low-level equivalent to altocumulus with some vertical development.
Clouds with Extensive Vertical Development (may extend through mmm moo atmosphere)	Cumulus (Cu)	Detached billowy clouds with flat bases and moderate vertical development. Sharply defined boundaries.
	Cumulonimbus (Cb)	Clouds with intense vertical development with characteristic anvil. May be tens of thousands of meters thick. Appear very dark when viewed from below. Can create violent weather.

Unusual Clouds:

─     Lenticular Clouds—waves formed by the passage of air over a topographic barrier.

─     Banner Clouds—isolated atop mountain peaks

─     Mammatus—found in margins of cumulonimbus clouds, formed by downdrafts, and sometimes are distorted by complex motions.

─     Nacreous Clouds—stratus clouds only observed at high latitudes.

─     Noctilucent Clouds—in the mesosphere, can illuminate the sky at high latitudes during the twilight hours. Noctilucent clouds

Other:

─   Aircraft Contrails—A type of ice cloud, know as contrails, is frequently caused by jet aircraft. The very hot engine exhaust contains considerable water vapor as a result of fuel combustion, and turbulence in the wake of the aircraft rapidly mixes the exhaust with the cold, ambient air. The mixing of warm, moist air with cold air can lead to saturation and, in this case, the rapid formation of ice crystals.