Science / Weather Glossary

Alberta Clipper: A fast moving, snow-producing weather system that originates in the lee of the Canadian Rockies. It moves quickly across the northern United States, often bring gusty winds and cold Arctic air.

Aleutian Low: A semi-permanent, subpolar area of low pressure located in the Gulf of Alaska near the Aleutian Islands. It is a generating area for storms and migratory lows often reach maximum intensity i . . . View Full Definition

Altimeter: An instrument used to determine the altitude of an object with respect to a fixed level. The type normally used by meteorologists measures the altitude with respect to sea level pressure.

Altimeter Setting: The pressure value to which an aircraft altimeter scale is set so that it will indicate the altitude above mean sea level of an aircraft on the ground at the location for which the value was . . . View Full Definition

Altitude: In meteorology, the measure of a height of an airborne object in respect to a constant pressure surface or above mean sea level.

Altocumulus: Composed of flattened, thick, gray, globular masses, this middle cloud genus is primarily made of water droplets. In the mid-latitudes, cloud bases are usually found between 8,000 and 18,000 . . . View Full Definition

Altocumulus Castellanus: A middle cloud with vertical development that forms from altocumulus clouds. It is composed primarily of ice crystals in its higher portions and characterized by its turrets, protuberances, . . . View Full Definition

Altostratus: This middle cloud genus is composed of water droplets, and sometimes ice crystals, In the mid-latitudes, cloud bases are generally found between 15,000 and 20,000 feet. White to gray in colo . . . View Full Definition

American Meteorological Society: An organization whose membership promotes the education and professional advancement of the atmospheric, hydrologic, and oceanographic sciences.

Anabatic Wind: A wind that is created by air flowing uphill. Valley breezes, produced by local daytime heating, are an example of these winds. The opposite of a katabatic wind.

Anemometer: An instrument that measures the speed or force of the wind.

Aneroid Barometer: An instrument for measuring the atmospheric pressure. It registers the change in the shape of an evacuated metal cell to measure variations on the atmospheric pressure. The aneroid is a thin . . . View Full Definition

Anomalous Propagation: This refers to the non-standard propagation of a beam of energy, radio or radar, under certain atmospheric conditions, appearing as false (non-precipitation) echoes. May be referred to as A.P.

Antarctic: Of or relating to the area around the geographic South Pole, from 90° South to the Antarctic Circle at approximately 66 1/2°South latitude, including the continent of Antarctica. Along the A . . . View Full Definition

Antarctic Ocean: Although not officially recognized as a separate ocean body, it is commonly applied to those portions of the Atlantic, Pacific, and Indian Oceans that reach the Antarctic continent on their . . . View Full Definition

Anticyclone: A relative pressure maximum. An area of pressure that has diverging winds and a rotation opposite to the earth's rotation. This is clockwise the Northern Hemisphere and counter-clockwise in . . . View Full Definition

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 . . . View Full Definition

Aphelion: The point on the earth's orbit that is farthest from the sun. Although the position is part of a 21,000 year cycle, currently it occurs around July, when the earth is about 3 million miles f . . . View Full Definition

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