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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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Absolute Humidity - The mass of water vapor in certain area of air.

Acid Rain - Precipitation that consists of sulfuric and nitric acids, caused by air pollution.

Acre-foot - The amount of water needed to cover one acre under a foot of water.

Adiabatic Pressure - The measure of the change in air pressure when it rises and falls.

Advection - Horizontal movement of any meteorological property, such as warmth or humidity.

Advection Fog - Fog formed by warm, humid air flowing over cool ground water.

Aeronomy - The study of upper atmospheres of planets, including Earth.

Air Mass - A large body of air that brings change in temperature, humidity, and precipitation.

Air Pressure - The weight of the air pressing on the Earth, essentially the air above us.

Altimeter - A special instrument pilots can use to determine the height of an airplane. They are like an accurate aneroid barometer and can be adjusted to weather changes. The change in air pressure is about 1/10 inch of mercury for every 100 feet higher or lower of the plane.

Altitude - The distance of an object above the surface of a planet, such as an airplane's distance from Earth.

Anemometer - A weather instrument that measures wind speed. The most widely used anemometer consists of three or four cups that spin according to the speed of the wind (which is most of the time in miles per hour). Sometimes, it is measured in knots (which is equal to 1.15 miles per hour).

Aneroid Barometer -  An instrument used to measure air pressure, using metal to tightly seal the air. The outside pressure squeezes the flexible metal, and the less pressure causes it to expand, giving a reading of what the air pressure is. A mercury barometer is basically mercury inside of a vacuum tube (about 32 inches high) that has an opening at the bottom to a container of mercury. Then, as the pressure increases, the mercury rises. A ruler is set next to the tube to show the height of the tube, giving the pressure reading wherever the mercury level is.

Anti-cyclone - An area of high atmospheric pressure.

Anvil - Upper area above cumulonimbus clouds or thunderheads that appear to be flattened.

Apparent Temperature - The measure of the "feeling" of the temperature with the combined humidity levels.  Also called the heat index.

Atmosphere - The layers of the atmosphere, including the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.

Barograph - An instrument used to record air pressure.

Barometer - An instrument  used to measure air pressure.

Beaufort Wind Scale - Scale used to classify wind speed at sea, developed by British Admiral Francis in 1805.

Biosphere - The layer of Earth that inhibits all living things.

Blizzard - Falling snow with winds greater than 35 miles per hour and visibility of one quarter of a mile or less over an extended period of time.

Chaos Theory - The theory that some systems, such as weather, are ultimately unpredictable because of the effects of small scale events that can't be included in the prediction equations.

Climate - The average weather over a long period of time in a certain place or during a certain season.

Clouds - Large masses of condensed water droplets that form high in the atmosphere above the dew point and at the right moisture levels.

Cloud Seeding - The use of silver iodide, dry ice, or other substances to possibly produce or increase precipitation.

Cold Front - The boundary created when a cold air mass collides with a warm air mass.

Condensation - The change of a vapor to a liquid.

Condensation Nuclei - Small particles in the air that attract water and produce condensation.

Convection - The transfer of heat by the movement within a substance or from one substance to another.

Convective Storms - Storms created by rising warm air; Thunderstorms.

Coriolis Effect - The force that causes Northern Hemisphere winds to curve to the right and Southern Hemisphere winds to curve to the left. First described by French scientist Gustave-Gaspard Coriolis in 1835.

Cyclone - An area of low atmospheric pressure with winds blowing around it, counter clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Often times cyclones bring warmer air, higher humidity, and precipitation over a long period of time.

Cryosphere - The Earth's ice.

Derecho - Thunderstorms in which produce straight-line winds.

Dew - Water droplets that mainly form on leaves, grass, and plants from the condensation of water vapor.

Dew Point - Measure of the temperature in which condensation of water vapor will be produced.

Down Draft - The burst of cool air that rushes downward, usually from a thunderstorm.

Doppler Radar - Use of the Doppler effect to determine the relative distance of precipitation from a source. One of the most important instruments meteorologists use in tracking a storm.

Downburst - Blasting of wind down from a thunderstorm or shower.

Electromagnetic Radiation - Energy generated by the sun, including heat energy and UV rays.

Evaporation - The change of a liquid to a gas or water to water vapor.

Fronts - Boundary between two air masses, usually consist of different temperature and densities.

Funnel Cloud - A rotating column of air extended down from a cloud but not touching the ground.

Greenhouse Effect - The trapping of heat energy inside of the Earth.

Gust Front - Wind flowing out from a thunderstorm.  Gust fronts sometimes create very strong surface winds as a result of a temperature change as the front passes.

Halo - Any type of arc or circles around the sun as a result of ice crystals from clouds.

High Pressure System - An area of high atmospheric pressure.  Highs generally create cooler, dryer temperatures, with little or no clouds.

Hook Echo - A signature on doppler radar that usually shows reflectivity of a "hook" shape which can give meteorologists a sign of turbulence within a storm or a possible tornado developing or already formed.

Hurricane - A tropical cyclone with wind speeds in excess of 74 miles per hour.

Iridescence - Colorful patches in clouds caused by sunlight passing through the water droplets.

Jet Stream - Fast-moving currents of air high in the atmosphere.

Knot - A unit of measuring for speeds of ships and is used in meteorology for wind speed.  One knot is one nautical mile per hour,  two knots would be two nautical miles per hour, and so on..  One knot is equal to 1.15 miles per hour (or .5144 m/s).  All meteorologists currently use knots for plotting wind speed on weather maps.

Latent Heat - Heat released into the air when water vapor condenses and forms clouds.

Lightning - A form of visible electrical discharge between rain clouds or between rain clouds and the ground.

Low Pressure System - A large mass of low pressure air that spins in a counterclockwise direction in the Northern Hemisphere (clockwise in the Southern Hemisphere) and usually brings cloudy skies and precipitation.

Mesocyclone -A rotating, upward moving column of air in a thunderstorm that can spawn tornadoes.

Meteorologist -A scientist who studies and predicts the weather.

Multicell Storms - Thunderstorms consisting of clusters of single cell thunderstorms.

NEXRAD - Next Generation Weather Radar system installed in the 1900s by The National Weather Service, in the Defense Department and the Federal Aviation Administration.

Occluded Front - A boundary between cool, cold, and warm air masses.

Ozone Layer - A layer high in the atmosphere that filters out most of the sun's dangerous ultraviolet rays.

Precipitation - Any kind of water falling from the sky, such as rain, drizzle, snow, hail, or freezing rain.

Pressure Gradient Force - The force that causes air to move from areas of high pressure toward areas of low pressure. 

Radar - A very popular instrument used to track precipitation by sending radio waves that bounce off water droplets and ice crystals. 

Radiosonde - An instrument that is usually sent up in the air with a weather balloon and supplies weather data to meteorologists from the ground level to the upper atmosphere. 

Rain Gauge - A weather instrument that measure rainfall.

Relative Humidity - The percentage of water vapor that the air can hold at a given time.  A relative humidity of 90 percent means that the air is nearly full of water vapor and may soon become saturated, or unable to hold additional water vapor.

Satellite - A weather instrument that orbits the earth, taking photographs and collecting measurements of the upper atmosphere.

Single Cell Storm - Thunderstorms consisting of a single cell.

Solar Radiation - Electromagnetic radiation coming from the sun, including sunlight, ultraviolet, and infrared radiation.

Squall - A sudden gusty wind, often accompanied by precipitation.

Squall Line - A line of thunderstorms. 

Stationary Front - The boundary between cold and warm air masses moving side by side.  Neither side advances.

Temperature - The amount of heat the air is holding.

Tornado - A strong, rotating column of air extending downward from the base of a cumulonimbus cloud to the ground.

Tropical Cyclone - A low-pressure system in which the central core is warmer than the surrounding atmosphere.

Tropical Storm - A tropical cyclone with 39 to 74 mile per hour winds.

Thunderstorm - Localized storms that produce lightning and therefore thunder.

Turbulence - Irregular movements of wind, such as gusts and lulls.

Updraft - The upward movement of warm air.  Updrafts can be found beneath and inside all types of cumulus clouds.

Velocity - The term used to describe wind speed.

Visibility - The farthest distance it is possible to see at any particular time.

Vortex - A spinning mass of air and clouds.

Warm Front - The boundary created when a warm air mass collides with a cold air mass.

Water Vapor - Water in its invisible gas form.

Wind - The sideways movement of air.

Wind Chill - How cool it feels with the combination of wind speed and temperature.

Wind Shear - Any sudden change in wind speed or direction.

Zonal Flow - A West-to-East flow of winds.