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ablation: The loss of snow cover from any snow or ice surface by melting, evaporation, or calving.
abrupt climate change: Climate change occurring so rapidly that human and natural systems have difficulty adapting.
absolute humidity: The actual weight of water vapor within a unit of volume of air.
absolute zero: The lowest temperature possible; -273.15 Celsius and -459.67 Fahrenheit.
acclimation: The process by which an organism adapts to climate changes in the environment.
acid rain: Sulfuric acid in raindrops due to atmospheric pollution from sulfur dioxide.
advisory: A forecast issued by the National Weather Service regarding weather conditions that might require caution.
air: The mixture of gases that forms the atmosphere of the Earth.
air pollution: Substances in the atmosphere that directly or indirectly causes harm to living things and property.
air pressure: Air has weight. Air pressure is the weight of the air, or atmosphere, pushing down on Earth. The closer you are to sea level, the higher the air pressure because there’s that much air above you. The higher you are, there is less air pressure. Barometers measure air pressure.
almanac: A calendar with astronomical and weather data.
altitude: Height expressed above sea level or ground level.
aridity: The level at which a climate does not receive enough life-promoting moisture.
atmosphere: The gaseous fluid surrounding a planet.
aurora: A luminous phenomenon seen in the night sky, caused by the interaction of solar wind and Earth’s magnetic field.
Aurora Australis: The aurora, or southern lights, of the Southern Hemisphere.
Aurora Borealis: The aurora, or northern lights, of the Northern Hemisphere.
autumn: Season of the year marking the transition from summer to winter.
average: arithmetical mean.
barometer: An instrument that measure air pressure.
barometric pressure: Air pressure.
black ice: Invisible ice.
blizzard : A major snowstorm with strong winds of 35 miles per hour or more. The most notorious blizzard was the “Great White Hurricane” that paralyized the East Coast of the United States in 1888. (See also Major Storms timeline.)
blustery: Strong winds generally 20 miles per hour or more.
breeze: A light wind ranging from 4 to 31 miles per hour.
brisk: Weather that feels invigorating.
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calm The absence of any motion of the air.
Celsius: Zero degrees is the melting point of ice (32 degrees Fahrenheit), while its 100-degrees is the boiling point of water (212 degrees Fahrenheit). The Celsius scale replaced the Centigrade scale in 1948.
Centigrade: This scale is now known as the Celsius scale..
chill: A moderate, but penetrating coldness.
chilly: A sensation of coldness severe enough to cause shivering.
clear: A sky without any visible clouds.
cloud : Little drops of water hanging in the atmosphere. Clouds come in a variety of shapes. The major types of clouds are cirrus (thin, feathery), cirrocumulus (small patches of white), cirrostratus (thin, white sheets), stratus (a low, gray blanket), cumulous (flat-bottomed, white, putty), and cumulonimbus (mountains of dark, heavy clouds). (See also What Kind of Cloudy Is It?)
condensation: The change of water vapor to liquid.
deluge: Extremely heavy rainfall that results in flooding.
depression: A low pressure area in the atmosphere.
desertification: The formation or increase of desert like conditions in a region.
drought : A long period of no rainfall in a region. Droughts can destroy crops, dry up water supplies, and sometimes lead to widespread hunger or famine. The lack of moisture in the soil can also cause dust storms. (See also Droughts and Heat Waves.)
dry: very little precipitation or moisture, as in a dry-climate.
Fahrenheit: A temperature scale in which the melting of ice is at 32 degrees (0 degrees Celsius), and water boils at 212 degrees (100 degrees Celsius).
flood: a great flowing or overflowing of water, esp. over land not usually submerged.
freeze: A condition that exists when the air temperature remains consistently below 0 degrees C (32 degrees F).
Global warming : The theory that the Earth's temperature is growing warmer. In the future, global warming is expected to have damaging consequences to human life and the Earth's ecosystems. Many climatologists believe that increasing concentrations of carbon dioxide and other “greenhouse gasses” in the atmosphere are the cause of global warming.
Green house effect: an atmospheric heating phenomenon, caused by short-wave solar radiation being readily transmitted inward through the earth's atmosphere but longer-wavelength heat radiation less readily transmitted outward, owing to its absorption by atmospheric carbon dioxide, water vapor, methane, and other gases; thus, the rising level of carbon dioxide is viewed with concern.
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hail : Pellets of ice and snow created within clouds, that then fall to Earth. Hailstones can sometimes be quite large and can cause significant damage. The largest hailstone ever recorded in the U.S. was found in Aurora, Neb., on June 22, 2003. It measured 7 in. in diameter and 18.7 in. in circumference. The costliest U.S. hailstorm took place on July 11, 1990, in Denver, Colorado. The total damage was $625 million.
humidity : The amount of water vapor in the air. Relative humidity is the amount of water in the air compared to the amount of water the air can hold at that temperature. When the relative humidity reaches 100%, the air has reached its dew point. Once the air reaches this point, the water vapor turns back into water in the form of rain, snow, clouds or fog.
Hurricane : Major storms with strong winds ranging from 40 m.p.h. to 150 m.p.h. Violent storms occurring in the region of the Atlantic Ocean are known as hurricanes. When they appear in the Pacific they are called typhoons. (See also Hurricane Season.)
ice: The solid phase of water. The volume of ice is about 10 percent greater than when the ice melts into liquid form.
jet stream: Occurring about 6 to 9 miles above the ground, the jet stream is a belt of very strong winds.
lightning : Flashes of electrical discharges moving through the atmosphere during thunderstorms. There are different types of lightning: forked lightning (a jagged streak), sheet or streak lighting (a broad flash across the sky), and very rarely as a ball lightning (an illuminated ball). (See also Lightning Advice.)
Meteorologist: A person professionally employed in the study or practice of meteorology.
Meteorology: The study of the atmosphere and all its phenomenon.
muggy: Calm air that is warm and extremely humid.
overcast: The sky covered by layers of clouds with no openings.
precipitation : Condensed moisture that falls to the earth as rain, sleet, snow, frost, or dew.
rain: liquid precipitation in the form of water droplets.
rainbow : The refraction (bending) of sunlight passing through raindrops or fog sometimes causes a beautiful arc of colors to appear in the sky for a brief period. The sun, the arc, and the person observing it must be aligned just so in order for the rainbow to be visible.
sleet : A mixture of falling rain and snow, or rain and ice pellets.
snow : When clouds become too heavy with humidity, water falls from them. In colder clouds, this water forms ice crystals that fall from the sky as snow.
spring: The season of the year marking the transition from winter to summer.
sultry: Oppressive weather characterized by calm air that is high in temperature and humidity.
summer: The season of the year marking the transition from spring to autumn.
sun: The closest star to the Earth (93 million miles).
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thermometer: An instrument that measures temperature.
thunder : The loud noise that follows lightning during a thunderstorm. You can estimate how many miles away a storm is by counting the number of seconds between the flash of lightning and the clap of thunder. Divide the number of seconds by five to get the distance in miles. The lightning is seen before the thunder is heard because light travels faster than sound.
tornado : A tornado is a dark funnel-shaped cloud made up of violently rotating winds that can reach speeds of up to 300 m.p.h. The diameter of a tornado can vary between a few feet and a mile, and its track can extend from less than a mile to several hundred miles. (See also Tornadoes.)
tsunami: Sea waves caused by earthquakes, submerged volcanic eruptions, or other under-sea disturbances.
typhoon : A hurricane taking place in the Pacific Ocean.
water cycle: The process of water changing from one state to another and its movement from one place to another. For example, when it rains, water drops fall to Earth. This water evaporates from the surface of Earth and enters the atmosphere as water vapor. The water vapor then condenses into droplets that form clouds.
wind chill : The wind chill temperature indicates how cold people feel when outside. As the wind increases, it draws heat from the body, driving down skin temperature and eventually the internal body temperature. The wind therefore makes it feel much colder. If, for example, the temperature is 0°F and the wind is blowing at 15 mph, the wind chill is –19°F. At this wind chill temperature, exposed skin can freeze in 30 minutes. (See also Revised Wind Chill Factor.)
winter: The season of the year marking the transition from Autumn to Spring.