Weather Watch Glossary

Air Mass - a large area of air with relatively the same temperature and moisture throughout.
Air Pressure - the force that is applied on everything on earth caused by the weight of the air. The average air pressure at sea level is 1013 millibars or 101.3 kilopascals.
Atmosphere - the layer of air around the earth that consists mainly of nitrogen and oxygen gases. Most of the air is found within the first 35 km above the earth’s surface.
Anemometer - an instrument that measures wind speed.
Barometer - an instrument that measures air pressure (measured in millibars or kilopascals)
Chinook - a dry, warm wind that blows down the eastern slopes of the Rocky Mountains. The warmth and dryness are mainly due to heating by compression as the air descends the mountain slope (also called "the Snoweater").
Climate - the average range of weather conditions at any place occuring over a long period of time.
Cloud - a mass of minute water droplets or ice crystals up in the sky.
Condense - to turn a gas into a liquid by cooling.
Convection current - the circulation of air or a liquid due to heating. As air is heated in one place, its particles speed up, pushing each other farther apart. Since now there are fewer air particles in the same space, warm air is less dense than cold air thus it rises. The cooler air moves in to replace the rising warm air. As the warm air rises, it cools because less heat is trapped higher up in the atmosphere. Eventually , this rising air begins to fall back down to the earth's surface and the cycle continues. This cycle sets up a convection current.
Cumulonimbus Cloud - A towering cloud that extends upward to levels of 6-7 km above the earth's surface. Strong updrafts and downdrafts are associated with this cloud generating heavy rain and often hail. Lightening and thunder are also characteristic of this cloud.
Learn about many different clouds: See the ''All-in-One'' Cloud Type Diagram!
Low Level Clouds

Stratus
Stratocumulus
Cumulus
Cumulonimbus

Medium Level Clouds

Nimbostratus
Altostratus
Altocumulus
Altocumulus Lenticularis

High-Level Clouds

Cirrus
Cirrocumulus
Cirrostratus
Dew point - the temperature at which the water vapour in the air condenses out into droplets of water forming precipitation.
Drizzle - very fine rain consisting of drops less than 0.5 mm in diameter.
Draft - a current of cold air coming into a room through an opening such as a window or door.
Drought - a serious shortage of precipitation.
Evaporate - to change a liquid into a gas by heating.
Fog - Clouds near the ground.
Front - the boundary between a warm and cold air mass. If the cold air is moving in to replace the warm air, the front is called a cold front. If the warm air mass is moving in to replace the cold air, the front is called a warm front.
Hail - round or irregular lumps of ice formed by movement of ice through super cooled moisture in the upper parts of thunderheads.
Humidity - a measure of the amount of moisture in the air.
Hurricane - a severe tropical storm in which winds with speeds in excess of 116 km/h (73 mph) blow around an area of intensely low pressure; towering clouds bring torrential rain. See the exodus as people evacuate North Carolina before Hurricane Bonnie arrives.
Kinetic Energy - Energy of moving particles such as atoms or molecules. The more heat added to particles, the more kinetic energy or motion they have.
Mass - the amount of matter (concentration of particles) per unit of volume of a substance, measured in grams or kilograms.
Meteorology - the study of weather.
Precipitation - the name for moisture that falls out of clouds.
Radiant Energy - Energy from the sun that travels in waves and does not require a medium for its transmission.
Relative Humidty - a measure of the amount of moisture in the air relative to the amount the air can possibly hold at that temperature. It is expressed as a percentage (%).
Saturate Air - Air that holds as much moisture as is possible at a particular temperature.
Sleet - super cooled rain that freezes onto cold surfaces upon contact.
Snow - a form of precipitation that comes in the form of flakes. Consists of clusters of ice crystals frozen together into six-sided shapes. Snow forms only when the air is cold enough to freeze the moisture as it condenses out of the air.
Temperature - the amount of heat in a substance. Expressed in degrees of Centrigrade or Fahrenheit.
Thermometer - an instrument used to measure temperature.
Tornado - a violently rotating column of air, usually less than 100 m (300 ft) in diameter, surrounding a core of extremely low air pressure. Wind speeds may exceed 320 km/h (200 mph).
Water Cycle - the evaporation of moisture from a body of water into the air, the condensation of this moisture into precipitation, and its run as a river or stream back to the body of water where it started.
Weather - the condition of the atmosphere with respect to heat/cold, wetness/dryness, clearness/cloudiness for a period of time.
Weight - the gravitational force the Earth exerts on an object. Weight is measured in Newtons.
Wind - the movement of air along the ground. Light air movements are called breezes.
Wind Chill - a simple measure of the chilling effect experienced by the human body when strong winds are combined with freezing temperatures. The larger the wind chill, the faster the rate of cooling. The wind chill is expressed in watts per square metre or in °C (an equivalent temperature).

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