Science / Weather Glossary

Landfall: The point at which a tropical cyclone's eye first crosses a land mass.

Landspout: A small, weak tornado, which is not formed by a storm-scale rotation. It is generally weaker than a supercell tornado and is not associated with a wall cloud or mesocyclone. It may be observ . . . View Full Definition

Lapse Rate: The change of an atmospheric variable, usually temperature, with height. A steep lapse rate implies a rapid decrease in temperature with height and is a sign of instability.

Latent Heat: The energy released or absorbed during a change of state.

Latitude: The location north or south in reference to the equator, which is designated at zero (0) degrees. Parallel lines that circle the globe both north and south of the equator. The poles are at 9 . . . View Full Definition

Leeward: The side of an object or obstacle, such as a ship's sail, a mountain, or a hill, furthest away from the wind, and therefore, protected from the direct force of the wind. The opposite of windward.

Lenticular Cloud: A cloud species which has elements resembling smooth lenses or almonds and more or less isolated. These clouds are caused by a wave wind pattern created by the mountains. They are also indic . . . View Full Definition

Level Of Free Convection (LFC): The level at which a parcel of saturated air becomes warmer than the surrounding air and begins to rise freely. This occurs most readily in a conditionally unstable atmosphere.

Lifted Index (LI): A measure of atmospheric instability that is obtained by computing the temperature that the air near the ground would have if it were lifted to a higher level and comparing it to the actual . . . View Full Definition

Lifting Condensation Level (LCL): The height at which a parcel of moist air becomes saturated when it is lifted dry adiabatically.

Light Waves: That part of the electromagnetic spectrum that contains visible light. The colors, from longest wave length to shortest, are red, orange, yellow, green, blue, indigo, and violet (ROY G. BIV).

Lightning: A sudden and visible discharge of electricity produced in response to the build up of electrical potential between cloud and ground, between clouds, within a single cloud, or between a cloud . . . View Full Definition

Line Echo Wave Pattern (LEWP): A wave-shaped bulge in a line of thunderstorms. It may often be seen as a 'S'-shaped radar echo signature and is often associated with severe weather.

Lithometeor: Atmospheric phenomena which affect the state of the atmosphere. They constitute dry particles that hang suspended in the atmosphere, such as dust, smoke, sand, and haze.

Lithosphere: The solid, outer portion of the earth's crust coupled to the rigid upper mantle. Part of the geosphere.

Long Wave Trough: A wave in the prevailing westerly flow aloft which is characterized by a large length and amplitude. A long wave moves slowly and is persistent. Its position and intensity govern weather pat . . . View Full Definition

Longitude: The location east or west in reference to the Prime Meridian, which is designated as zero (0) degrees longitude. The distance between lines of longitude are greater at the equator and smalle . . . View Full Definition

Low Clouds: A term used to signify clouds with bases below 6,000 feet and are of a stratiform or a cumuliform variety. Stratiform clouds include stratus and stratocumulus. Cumuliform clouds include cumu . . . View Full Definition

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