Air mass A large body of air with relatively uniform characteristics such as temperature and humidity.
Altimeter A special type of aneroid barometer used in airplanes to measure altitude.
Aneroid barometer A device to measure air pressure that uses an aneroid, which is a sealed, flexible metal bellows with some air removed that expands and contracts with air pressure changes.
Atmosphere The air surrounding Earth.
Barograph A device for recording air pressure.
Barometer A device for measuring air pressure.
Blizzard Snow falling with winds faster than 35 mph and visibility of 1/4 mile or less over an extended time.
Climate Average weather of an area over a long time, usually 30 years.
Climate model Mathematical model containing equations that describe climatic interactions.
Cold front A warm-cold air boundary with the cold air advancing.
Condensation The change of a vapor to liquid.
Conduction Transfer of heat within a substance or from one substance to another by inter-molecular action.
Continental air mass An air mass that forms over land, making it generally dry. It may be warm or cold.
Convection Transfer of heat by the movement of the heated material. In meteorology, the up and down air motions caused by heat.
Coriolis Effect The apparent curving motion of anything, such as wind, caused by Earth's rotation. It was first described in 1835 by French scientist Gustave-Gaspard Coriolis.
Cyclone An area of low atmospheric pressure with winds blowing around it, counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere.
Doppler radar Radar that measures speed and direction of a moving object, such as wind.
Downburst Wind blasting downward through the air. It may be due to a thunderstorm or shower.
Drizzle Falling water drops with diameters less than .02 inch.
Drought Period of abnormal dryness for a particular region.
Electromagnetic radiation Energy that moves in the form of disturbances in electrical and magnetic fields. Light and radio waves are examples.
El Niño Linked ocean and atmospheric events that have worldwide effects, characterized by warming of water in the tropical Pacific from around the International Date Line to the coast of Peru.
Extratropical cyclone A large-scale weather system with a low-pressure center that forms outside the tropics.
Flash flood Flooding with a rapid water rise.
Fog A cloud with its base on the ground.
Fujita Scale A scale created by Theodore Fujita for classifying tornadoes according to their rotational wind speed and the damage they cause.
Funnel cloud A rotating column of air extending from a cloud but not reaching the ground.
GOES Geostationary Operational Environmental Satellite, a U.S. weather satellite in an orbit that keeps it above the same place on the equator.
Gulf Stream A warm ocean current that flows from the Gulf of Mexico across the Atlantic to the European coast. It helps warm Western Europe.
Gust front The boundary between cold air flowing downward out of a thunderstorm and the warmer air at the surface. Its passage is similar to that of a strong cold front.
Hail Balls of ice that grow in thunderstorm updrafts.
Heat lightning Glowing flash in clouds. No thunder is heard because heat lightning is too far away.
High An area of high-atmospheric pressure, also called an anticyclone.
Hurricane A tropical cyclone with winds of 74 mph or more.
Hydrosphere Comprises all the water on Earth.
Intertropical Convergence Zone The area near the equator called "The Doldrums" by sailors, where the trade winds converge.
Inversion Stable air condition in which air near the ground is cooler than air at a higher altitude.
Jet stream A narrow band of wind in the upper atmosphere with speeds greater than 57 mph.
Latent heat Energy stored when water evaporates into vapor or ice melts into liquid. It is released as heat when water vapor condenses or water freezes.
Latitude The distance on Earth's surface measured in degrees north and south of the equator.
Lightning A visible discharge of electricity produced by a thunderstorm.
Longitude The distance on Earth's surface measured in degrees east and west from the prime meridian.
Low An area of low-atmospheric pressure.
Maritime air mass An air mass that forms over an ocean, making it humid. It may be warm or cold.
Meridional flow A north to south to north flow of high-altitude winds.
Mesocyclone A rotating, upward moving column of air in a thunderstorm that can spawn tornadoes.
Mesoscale In meteorology, weather systems and events up to about 250 miles across.
Meteorological bomb An extratropical cyclone in which the center pressure drops an average of one millibar an hour for 24 hours. Usually refers to storms off the U.S. East Coast.
Microburst A downburst less than 2.5 miles in diameter.
Mid latitudes The region of Earth between the polar and tropical regions, between latitudes 23.5 degrees and 66.5 degrees.
Millibar A metric unit of air pressure measurement. The average atmospheric pressure at sea level is 1013 millibars.
Moist adiabatic lapse rate The variable rate at which rising air cools or sinking air warms when water is changing phases in the air.
Monsoon Persistent, widespread, winds that seasonally reverse directions. Usually summer winds from the ocean bring rain, while winter winds from the land are dry.
Multicell storms Thunderstorms consisting of clusters of single cell thunderstorms.
National Climatic Data Center (NCDC) The National Oceanic and Atmospheric Administration office in Asheville, NC, that keeps climate records.
National Hurricane Center (NHC) National Weather Service office in Coral Gables, FL, that tracks and forecasts hurricanes and other weather in the Atlantic, Gulf of Mexico, Caribbean Sea, and parts of the Pacific.
National Meteorological Center (NMC) National Weather Service center in Camp Springs, MD, that prepares worldwide computer forecasts. Hurricane and Severe Storms centers are part of NMC.
National Severe Storms Forecast Center National Weather Service center in Kansas City, MO, that issues watches for severe thunderstorms and tornadoes across the nation.
National Severe Storms Laboratory (NSSL) National Oceanic and Atmospheric Administration Laboratory in Norman, OK, that studies severe thunderstorms.
National Weather Service Federal agency that observes and forecasts weather. Formerly the U.S. Weather Bureau, it is part of the National Oceanic and Atmospheric Administration, which is part of the Department of Commerce.
Numerical forecasting or prediction Use of computers to solve mathematical equations and produce weather forecasts.
100-year floods Water levels that, on average, should occur once a century. This is the same as a water level with a 100 to 1 chance of occurring in any single year.
Ozone Form of oxygen with molecules that consist of three oxygen atoms compared to two atoms for ordinary oxygen molecules.
Ozone hole Zone of decreased ozone content that forms in the stratosphere over Antarctica each spring.
Prefrontal squall lines Lines of thunderstorms ahead of an advancing cold front.
Pressure gradient force Force acting on air caused by air pressure differences.
Rain Falling water drops with a diameter greater than .02 inch.
Rainbow Arc or circle of colored light caused by the refraction and reflection of light by water droplets.
Relative humidity The ratio of the amount of water vapor actually in the air compared to the maximum amount of water vapor the air can hold at its current temperature and pressure. This is expressed as a percentage.
Ridge An elongated area of high atmospheric pressure, running generally north-south, at the surface or aloft.
Saffir-Simpson Hurricane Damage Potential Scale A 1-5 scale, developed by Robert Simpson and Herbert Saffir that measures hurricane intensity.
Sea breeze Winds blowing inland from any body of water.
Severe thunderstorm A thunderstorm with winds faster than 57 mph or hailstones 3/4 of an inch or larger in diameter.
Short wave A bend, or wave of wind, only tens of miles long, that moves along in the wind flow of the upper atmosphere.
Solar energy The energy produced by the sun.
Squall line A line of thunderstorms.
Stable air Air in which temperature and moisture discourage formation of updrafts and downdrafts. Clouds will be low and flat Any precipitation will be steady.
Stationary front A warm-cold air boundary with neither cold nor warm air advancing.
Storm surge Quickly rising ocean water levels associated with hurricanes that can cause widespread flooding.
Storm tracks Paths that storms generally follow.
Stratosphere The layer of the atmosphere from about 7 to 30 miles up.
Supercell A fierce thunderstorm that usually lasts several hours, often spinning out a series of strong tornadoes.
Synoptic scale Large-scale weather events and systems, generally more than 200 miles across.
Thunder Sound produced by a lightning discharge.
Thunderstorms Localized storms that produce lightning, and therefore, thunder.
Tornado A strong, rotating column of air extending from the base of a cumulonimbus cloud to the ground.
Trade winds Global-scale winds in the tropics that blow generally toward the west in both hemispheres.
Transpiration Release of water vapor into the air by plants.
Tropical cyclone A low-pressure system in which the central core is warmer than the surrounding atmosphere.
Tropical depression A tropical cyclone with maximum sustained winds near the surface of less than 39 mph.
Tropical disturbance Rotary air circulation 160 to 300 kilometers across associated with a low pressure area over the tropical ocean.
Tropical storm A tropical cyclone with 39 to 74 mph winds.
Tropics The region of Earth between latitude 23.5 degrees north--the Tropic of Cancer--southward across the equator to latitude 23.5 degrees south--the Tropic of Capricorn.
Tropopause The boundary between the troposphere and the stratosphere.
Troposphere The lower layer of the atmosphere, extending from the surface up to 7 or 8 miles above the earth.
Typhoon A tropical cyclone with winds more than 75 mph and located in the north Pacific, west of the international date line.
Warm Front A warm-cold air boundary with warm air advancing.
Water Vapor Water in a gaseous state.
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