Science / Weather Glossary

Cumuliform: Clouds composed of water droplets that exhibit vertical development. The density of the droplets often blocks sunlight, casting shadows on the earth's surface. With increasing vertical heigh . . . View Full Definition

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, an . . . View Full Definition

Cumulonimbus Mammatus: A portion of a cumulonimbus cloud that appears as a pouch or udder on the under surface of the cloud. Although they do not cause severe weather, they often accompany storms. They may slowly . . . View Full Definition

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. Th . . . View Full Definition

Cumulus Congestus: A strongly sprouting cumulus cloud with generally sharp outlines and often with great vertical development. It may occur as tower-like clouds with cauliflower tops. These clouds may produce . . . View Full Definition

Cumulus Fractus: Cumulus clouds that appear in irregular fragments, as if they had been shred or torn. Also appears in stratus clouds (called stratus fractus), but not in cirrus clouds.

Cumulus Humilis: Cumulus clouds with little or no vertical development characterized by a generally flat appearance. Their growth is usually limited by a temperature inversion, which is marked by the unusual . . . View Full Definition

Cumulus Mediocris: Cumulus clouds characterized by moderate vertical development with upper protuberances not very marked in appearance. This cloud does not produce precipitation, but could develop into toweri . . . View Full Definition

Current: A horizontal movement of water, such as the Gulf Stream off the east coast of North America, or air, such as the jet stream.

Cut-Off High: A warm high which has become displaced and is on the polarward side of the jet stream. It occurs mostly during the spring and is most frequent over northeastern Siberia, Alaska, and Greenlan . . . View Full Definition

Cut-Off Low: A closed cold core low completely removed from the primary westerly flow. Cutoff lows may remain detached from the westerlies for days while exhibiting very little forward (eastward) progres . . . View Full Definition

Cyclogenesis: The process that creates a new low pressure system or cyclone, or intensifies a pre-existing one. It is also the first appearance of a trough.

Cyclone: An area of closed pressure circulation with rotating and converging winds, the center of which is a relative pressure minimum. The circulation is counterclockwise in the Northern Hemisphere . . . View Full Definition

Cyclonic Flow: Winds that blow in and around a cyclone, that is counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere.

D-Value: The deviation of actual altitude along a constant pressure surface from the standard atmosphere altitude of that surface.

Daily Mean: The average temperature for a day computed by averaging either the hourly readings or, more commonly, the maximum and minimum temperatures.

Daltons Law: States that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the gases. Formulated by John Dalton, an English physicist.

Data Buoys: Buoys placed throughout the Gulf of Mexico and along the Atlantic and Pacific coasts of the United States that relay information on air and water temperature, wind speed, air pressure, and w . . . View Full Definition

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