Cirrus
One of the three basic cloud forms (the others are cumulus and stratus). It is also one of the three high cloud types. Cirrus are thin, wispy clouds composed of ice crystals and often appear as veil patches or strands. In the mid-latitudes, cloud bases are usually found between 20,000 to 30,000 feet, and it is the highest cloud that forms in the sky, except for the tops, or anvils, of cumulonimbus, which occasionally build to excessive heights.
Cloud
A visible collection of minute particle matter, such as water droplets and/or ice crystals, in the free air. A cloud forms in the atmosphere as a result of condensation of water vapor. Condensation nuclei, such as in smoke or dust particles, form a surface upon which water vapor can condense.
Cumulus
One of the three basic cloud forms (the others are cirrus and stratus). It is also one of the two low cloud types. A cloud that develops in a vertical direction from the base (bottom) up. They have flat bases and dome- or cauliflower-shaped upper surfaces. The base of the cloud is often no more than 3,000 feet above the ground, but the top often varies in height. Small, separate cumulus are associated with fair weather (cumulus humilis). With additional heating from the earth’s surface, they can grow vertically throughout the day. The top of such a cloud can easily reach 20,000 or more into the troposphere. Under certain atmospheric conditions, these clouds can develop into larger clouds, known as towering cumulus (cumulus congestus), and may produce a rain shower. Further development may create a cumulonimbus.
Stratus
One of the three basic cloud forms (the others are cirrus and cumulus. It is also one of the two low cloud types. It is a sheetlike cloud that does not exhibit individual elements, and is, perhaps, the most common of all low clouds. Thick and gray, it is seen in low, uniform layers and rarely extends higher than 5,000 feet above the earth’s surface. A veil of stratus may give the sky a hazy appearance. Fog may form from a stratus cloud that touches the ground. Although it can produce drizzle or snow, it rarely produces heavy precipitation. Clouds producing heavy precipitation may exist above a layer of stratus.
High Clouds
A term used to signify cirriform clouds that are composed of ice crystals and generally have bases above 20,000 feet. The main types of high clouds are cirrus, cirrocumulus, and cirrostratus. This altitude applies to the temperate zone. In the polar regions, these clouds may be found at lower altitudes. In the tropics, the defining altitudes for cloud types are generally higher.
Ice Crystals
Precipitation in the form of slowly falling, singular or unbranched ice needles, columns, or plates. They make up cirriform clouds, frost, and ice fog. Also, they produce optical phenomena such as halos, coronas, and sun pillars.
Middle Latitudes
The latitude belt roughly between 35 and 65 degrees North and South. May be referred to as the temperate region.
Anvil
The upper portion of a cumulonimbus cloud that becomes flat and spread-out, sometimes for hundreds of miles downstream from the parent cloud. It may look smooth or fibrous, but in shape, it resembles a blacksmith’s anvil. It indicates the mature or decaying stage of a thunderstorm.
Cumulonimbus
A vertically developed cumulus cloud, often capped by an anvil-shaped cirriform cloud. Also called a thunderstorm cloud, it is frequently accompanied by heavy showers, lightning, thunder, and sometimes hail, tornadoes or strong, gusty winds.