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Weather Glossary


the mixture of gases that surrounds the earth. The principle gases in dry air are: Nitrogen at 78.084%, Oxygen at 20.946%, Argon at .93%, and Carbon Dioxide .03%
air pressure
the weight of air pressing down on earth. Air pressure can change from place to place, and this causes air to move, flowing from areas of high pressure toward areas of low pressure. It is the same as barometric pressure. The measurement can be expressed in millibars(mb) or in inches of mercury(Hg)
is a device for measuring wind speed either mechanically, electronically, or by pressure
the blanket of air around the earth


an instrument used to measure atmospheric pressure. Examples include the aneroid barometer and the mercurial barometer
barometric pressure
the same as air pressure
a severe weather condition characterized by low temperatures, winds 35 mph or greater, blowing snow that can reduce visibility to 1/4 mile or less for more than 3 hours


cirrus cloud
high, thin, wispy clouds usually above 18,000 feet, composed of ice crystals Photo
the historical record of average weather conditions in a certain place or certain season. Weather may change from day to day, but climate changes only over hundreds or thousands of years
the study of climate and its phenomena
a visible mass of minute water and/or ice particles in the atmosphere suspended above the earth's surface
the process by which water vapor undergoes a change in state from a gas to a liquid. It's opposite is evaporation
cumulonimbus cloud
a vertical cloud, often capped by an anvil shaped cloud. This cloud is also called a thundercloud. A cumulonimbus cloud can produce tornadoes, hail, lightning, strong winds and heavy rain
cumulus cloud
puffy in appearance, cumulus clouds form when warm, moist air is forced upward. They signal fair, clear weather. Photo
a low pressure system with an atmospheric circulation that rotates counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere


condensation in the form of small water drops that form on grass and other object near the ground when the temperature has fallen to the dewpoint. Dew generally forms during the nighttime hours and evaporates by mid to late morning
the temperature at which water starts to condense out of a particular air mass. The dew point temperature changes when the moisture content of the air changes
doppler radar
weather radar that measures the direction and speed of a moving object, such as drops of precipitation
a severe localized downdraft of cool air from a thunderstorm or shower, which can create damaging winds
a period of prolonged dry weather leading to a shortage of water


El Nino
the cyclical warming of East Pacific Ocean sea water temperatures off the western coast of South America that affect weather patterns in the United States. This occurs when warm equatorial Pacific waters move in and displace the colder waters, cutting off the upwelling process
the physical process by which water is transformed into water vapor. It is the opposite physical process of condensation


flash flood
a rapid rise in water, usually within 12 hours of a period of heavy rain that comes with little or no advance warning
a cloud near the the ground
a statement of what the weather will be in the future
freezing drizzle
drizzle, falling as a liquid, but freezing when it lands on colder ground
freezing rain
rain that falls as liquid and freezes upon impact to form a coating of glaze on the colder ground
the covering of ice crystals that forms on surfaces whose temperature is below freezing
funnel cloud
a rotating, funnel-shaped column of air extending down from a thundercloud


geostationary satellite
an orbiting weather satellite that maintains the same position over the equator during the earth's rotation. Also known as GOES, an acronym for Geostationary Operational Environmental Satellite
global warming
a theory that increased concentrations of greenhouse gases are causing the Earth’s surface temperature to warm
greenhouse effect
the warming of the earth's lower atmosphere primarily due to carbon dioxide and water vapor which permit the sun's rays to heat the earth but prevents some heat-energy from escaping back into space
greenhouse gases
are the gases present in a planet's atmosphere which trap heat from the sun. On Earth these gases keep the temperature of the planet within livable levels, but on Venus they trap so much heat that the planet's surface temperature is almost 900° Farhenheit. See greenhouse effect


precipitation in the form of balls or irregular pieces of ice, which comes in different shapes and sizes. Individual lumps are called hailstones
a suspension of fine dust and/or smoke particles in the air
a form of energy transferred between two systems by virtue of a difference in temperature
high pressure system
an area of relative pressure maximum that has a rotation opposite to the earth's rotation. This is clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. It is the opposite of an area of low pressure or a cyclone
the amount of water vapor in the air
the name for a tropical cyclone with sustained winds of 74 miles per hour (65 knots) or greater in the North Atlantic Ocean, Caribbean Sea, Gulf of Mexico, and in the eastern North Pacific Ocean. It is called a typhoon in the western Pacific and a cyclone in the Indian Ocean
hydrologic cycle
also called the water cycle, it is the vertical and horizontal transport of water in all its states between the earth, the atmosphere, and the seas


water in a solid state


La Nina
a widespread cooling of the surface waters of the eastern tropical Pacific Ocean. It’s the opposite of El Nino
a rapid, visible discharge of electricity hotter than the surface of the sun. Lightning is caused by the build up of electrical potential between cloud and ground, between clouds, or between clouds and the surrounding air
low pressure system
an whirling mass of warm, moist air that rotates in the same direction as the Earth...counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. It is also known as a cyclone. It usually brings stormy weather with strong winds


the science that deals with the atmosphere, especially with weather and weather forecasting
the science that deals with the atmosphere, especially with weather and weather forecasting. What is Meteorology?
the monsoon is associated primarily with the moisture and heavy rains that arrive with the southwest flow of air across southern India. This pattern is most evident on the southern and eastern sides of Asia


a cloud that exhibits a combination of rain or snow, and sometimes the base of the cloud cannot be seen because of the heaviness of precipitation. They are generally associated with fall and winter conditions, but can occur during any season


when the sky is completely covered by clouds
ozone layer
an atmospheric layer that contains a high proportion of oxygen that exists as ozone. It acts as a filtering mechanism against incoming ultraviolet radiation. It is located between 9.5 and 12.5 miles above the Earth's surface. Ozone at the surface is not healthy for humans to breathe


any forms of water, liquid or solid, that falls from clouds and reaches the ground. This includes, drizzle, hail, rain, snow, sleet


acronym for RAdio Detection And Ranging. An electronic instrument used to detect distant objects and measure their range by how they scatter or reflect radio energy. Precipitation and clouds are detected by measuring the strength of the electromagnetic signal reflected back
an arc featuring all colors of the visible light spectrum (red, orange, yellow, green, blue, indigo, and violet). Rainbows are caused by the bending of sunlight passing through raindrops. The bow is always observed in the opposite side of the sky from the sun
rain gauge
this instrument gathers and measures the amount of liquid precipitation over a period of time; it isalso known as an udometer or a pluviometer
is a term used to describe the flow of water, from rain, snowmelt, or other sources, over land


saturation point
the temperature when the atmosphere has the maximum water vapor in it for the existing temperature
also known as ice pellets, it is winter precipitation in the form of small bits of ice
frozen precipitation in the form of white or translucent ice crystals
stratus cloud
is a sheetlike cloud that is, perhaps, the most common of all low clouds. Thick and gray it rarely extends higher than 5,000 feet above the earth's surface. Photo


the measure of molecular motion or the degree of heat of a substance
an instrument used for measuring temperature. The different scales used in meteorology are Celsius, Fahrenheit, and Kelvin or Absolute
the explosive sound of gases expanding as they are heated by lightning
produced by a cumulonimbus cloud, it is a short weather event characterized by thunder, lightning, gusty surface winds, turbulence, hail, icing, precipitation, moderate to extreme up and downdrafts, and under the most severe conditions, tornadoes
a violently rotating column of air attached to a thundercloud and in contact with the surface of the earth
the process by which water in plants is transferred as water vapor to the atmosphere
the bottom six to ten miles of the atmosphere where all weather takes place
an ocean wave that is formed by an underwater earthquake or landslide, or volcanic eruption. It may travel unnoticed across the ocean for thousands of miles from its point of origin and builds up to great heights over shallower water. Also known as a seismic sea wave, and incorrectly, as a tidal wave
a the name for a hurricane in the Western Pacific Ocean


given when a severe weather event is about to happen or already is happening
given when conditions are favorable for a severe weather event
water cycle
it is the vertical and horizontal transport of water in all its states between the earth, the atmosphere, and the seas. same as hydrological cycle
weather satellite
monitors the weather and climate of the Earth from space
air that flows, usually horizontally, in relation to the earth's surface. There are four areas of wind that are measured: direction, speed, character (gusts and squalls), and shifts. Surface winds are measured by wind vanes and anemometers, while upper level winds are detected through pilot balloons, rain, or aircraft reports
wind chill index
the calculation of temperature that takes into consideration the effects of wind and temperature on the human body
wind shear
the change in wind speed and/or direction with height above the surface of the earth. Read more

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