Weather Words - C | Weather | WGNTV.com | WGN TV

Weather Words - C

-- C --

Calf: A large floating chunk of ice split off from a glacier, iceberg or a floe.

Calibration: The process whereby the reading of a measuring instrument (such as the digital readout of a thermometer) is related to the actual value of the variable being measured (such as the air temperature).

California's highest temperature: 134 degrees F on July 10, 1913, at Greenland Ranch in Death Valley (elevation 178 feet below sea level). This is also the highest temperature ever recorded in the United States.

Calm: The absence of apparent motion of the air. Smoke rises vertically and water surfaces are smooth and mirror-like. In the U.S., the wind speed is reported as calm when its speed is less than one m.p.h. More generally, a period or condition of freedom from storms, high winds or (for boaters) conditions of rough water.

Calorie: A unit of heat; the amount of heat required to raise the temperature of one gram of water one degree Celsius. More precisely, the heat required to raise the temperature of one gram of water from 14.5 to 15.5 degrees C.

Canada's first official weather observation: Sept. 6, 1840, in Toronto, Ontario; taken at King's College, University of Toronto, by members of the British Royal Artillery.

Canada's most costly weather disaster: The ice storm of Jan. 5-9, 1998, across southeast Canada (northern New England also affected). Glaze accumulated 3-4 inches; 56 died, 4 million (including Montreal) were without power.

Canada's second-worst tornado: On July 31, 1987, a massive tornado tore through Edmonton, Alberta, leaving 27 dead, 253 injured and hundreds homeless. Damage estimate exceeds 250 million dollars.

Canada's worst tornado: The Regina, Saskatchewan, tornado of Sunday, June 30, 1912; known popularly as the Regina Cyclone. Twenty-eight were killed when an F4 tornado tore through the core of the city. This is Canada's highest tornado death toll.

Canadian air: An air mass that has acquired its major characteristics -- cool, dry, relatively free of pollution and contaminants such as pollen and dust -- over the Canadian interior.

Canadian lightning disaster: On June 26, 1930, lightning struck the drillship John B. King in the St. Lawrence River, igniting a store of onboard dynamite. The resulting explosion killed 30, injured 11.

Cap: A layer of warm air, a few thousand feet above the surface, that suppresses or delays thunderstorm development. Warm air rising into this layer is cooler than the surrounding air and cannot rise further.

Cap cloud: An approximately stationary cloud on or hovering above an isolated mountain peak. It is formed by the cooling and condensation of moist air blowing up and over the peak.

Capped: Descriptive of an atmospheric condition in which warm air aloft suppresses the development of thunderstorms.

Carbon: The element carbon combines with many other substances to form a huge number of compounds that permeate our environment. For example, carbon exists in the atmosphere as the gaseous compound carbon dioxide.

Carbon dioxide: A minor constituent gas of the atmosphere (0.03 percent), but very important because it strongly absorbs and emits long-wave infrared radiation which greatly influences the temperature of the atmosphere. Although carbon dioxide exists only as a trace component of the atmosphere (amounting to only 0.03 percent by volume of dry air), it is such a powerful greenhouse gas that it causes the Earth's temperature to be about 50 degrees F warmer than it would be without its presence.

Carbon dioxide concentration: In 1860, carbon dioxide existed in the atmosphere in a concentration of about 288 parts per million (ppm). By 1900 its concentration was at 291 ppm, 332 ppm in 1980, and 370 ppm in 1999; its concentration is expected to double in the 21st century.

Carbon dioxide emissions: The United States annually releases five times as much carbon dioxide (a greenhouse gas) into the atmosphere as India, even though India's population is about four times larger than that of the United States. It is estimated that seven billion tons of carbon dioxide (a greenhouse gas) are emitted into the atmosphere annually by the United States, and that is 25 percent of the world total. The United States has 5 percent of the world's population.

Carbon monoxide: A colorless, tasteless, odorless, highly toxic gas. It is found in minute quantities in the free atmosphere, and it is also produced by the incomplete combustion of carbonaceous fuels.

Cardinal temperatures: The highest and lowest temperatures that define the limits of growth of an organism; also, the optimum temperature at which growth proceeds with greatest speed.

Cardinal winds: Winds blowing from the four cardinal points of the compass (north, east, south, west).

Carrier, Willis H.: (1876-1950) The Father of the Air Conditioning Industry. The American mechanical engineer who, at the age of 25, built the first scientific air conditioning system in 1902.

Castellanus: A cloud species of which at least a portion of its upper part presents vertically developed protuberances, usually taller than they are wide, that give the cloud a turreted appearance.

Catch: The amount of precipitation captured by a rain gauge.

Category 5 hurricane: The most intense hurricane (sustained winds above 155 m.p.h.) on the Saffir-Simpson hurricane scale. Since 1900, only three hurricanes were at category 5 intensity when they made landfall in the United States: Camille (August 17, 1969; Mississippi), the Labor Day Hurricane (Sept. 2, 1935; Florida Keys) and Andrew (Aug 24, 1992; S. Florida).

Cb: (pronounced see-bee) Weather jargon for a cumulonimbus cloud, the cloud that produces thunderstorms.

Ceiling: In meteorology and aviation, the height above the Earth's surface of the lowest deck of opaque clouds whose bases cover five-eighths or more of the sky.

Cell: In weather radar usage, the precipitation echo associated with a single thunderstorm during its life cycle, usually lasting about a half hour, but in supercell thunderstorms it can be several hours.

Celsius: A temperature scale adopted in 1948 to replace the Centigrade scale. Its zero point is the melting point of ice (32 degrees F) and its 100-degree point is at the boiling point of water (212 degrees).

Celsius, Anders: (1701-1744) The Swedish astronomer and physicist who, in 1742, presented a paper describing a thermometer on which the interval between the freezing and boiling points of water was divided into 100 equal parts.

Centigrade: A temperature scale, introduced in 1743, which has its zero point at the melting point of ice and its 100-degree point at the boiling point of water. One centigrade degree is 9/5 of a Fahrenheit degree. The centigrade scale is now known as the Celsius scale.

Central pressure: The air pressure at the center of a low or high pressure system; the highest pressure in a high and the lowest pressure in a low, referring (on a weather map of surface weather conditions) to the air pressure value reduced to sea level.

Chaff: Minute strips of aluminum-covered plastic dropped from military aircraft in order to generate false echoes on radars and give military radar operators practice in identifying and measuring radar echoes. Those false echoes look like precipitation echoes.

Challenger expedition: The 1872-1876 voyage of H.M.S. Challenger, a ship outfitted by the British Admiralty to study the world's oceans. The expedition is considered the birth of the science of oceanography in that it was the first extended voyage for the sole purpose of collecting scientific data.

Chance: As used in issuances of the Chicago National Weather Service, the probability term used to describe a weather event (like rain) whose probability of occurrence is believed to be either 30 percent, 40 percent, or 50 percent.

Chance of precipitation: As used in weather forecasts issued by the Chicago National Weather Service, a precipitation event whose probability of occurrence is believed to be either 30 percent, 40 percent or 50 percent.

Chaos theory: The general principle that internal instabilities cause complex behavior in a system. Because the atmosphere is internally unstable and cannot be exactly specified at a particular instant, the atmosphere is said to be a chaotic system.

Cheimaphobia: The irrational or morbid fear of cold or winter.

Cheimatophobia: The irrational fear of cold or low temperatures.

Cherrapunji, India: One of the world's wettest places. Average annual rainfall is 428 inches; holds world record for wettest 12 consecutive months (1,041 inches in 1860-61) and for wettest month (366.41 inches, in July, 1861).

Chill: A moderate but penetrating coldness.

Chilly: Producing a sensation of coldness; cold enough to cause shivering.

China flooding: China, the world's most populous nation, has suffered the ravages of flooding more severely than any other nation. In 1998, 240,000,000 were affected by floods, 3,000 died; 30,000 perished in a 1954 flood and famine; 500,000 in 1938; 3,700,000 from flood and famine in 1931; 550,000 in 1889.

Chinook: A warm dry wind that blows down the eastern slopes of the Rocky Mountains. The name given to the foehn on the eastern slopes of the Rocky Mountains. It is most frequent in the winter months in Montana, Wyoming. Colorado and southern Alberta, Canada. Temperatures rise rapidly, snow melts quickly. At Havre, Mont., a temperature rise from 11 degrees F to 42 occurred in three minutes.

Chionophobia: The irrational or morbid fear of snow.

Chlorofluorocarbons (CFCs): Compounds formerly used as aerosol propellants, refrigerants and solvents, but banned by international agreement on January 1, 1996, because they break down and release chlorine that reacts with and destroys the stratospheric ozone layer.

Chocolatero: A moderately strong wind blowing from the north in the Gulf of Mexico region of Mexico, often carrying dust and sand; also known as a chocolate gale.

Christmas Tree Ship: The Rouse Simmons, owned/operated by Herman Schuenemann, who shipped Christmas trees from Wisconsin to Chicago via Lake Michigan every year. It sank off Two Rivers, Wisc., during a gale on Nov. 23, 1912, taking Schuenemann and 16 others to their deaths.

Chun fung: In Chinese, literally spring wind. In China, a spring breeze; also, pleasant weather at the start of the spring season.

Cirriform: Descriptive of high clouds composed of small particles, usually ice crystals, which are fairly widely dispersed and therefore relatively transparent and whitish in appearance; descriptive of cirrus clouds (high-level clouds consisting of ice crystals). Cirriform clouds occur frequently at Chicago all through the year.

Cirrus clouds: A principal cloud type, composed of ice crystals, in the form of white, delicate filaments, white patches, or narrow white bands. Their appearance is often feather-like and without shading.

City blink: The brightening of the base of a cloud layer over a city, caused by the reflection from the clouds of the city's lights. Given favorable weather conditions, the lights of metropolitan Chicago generate a pale orange blink that is visible 100 miles or more from the city.

City sky: The bright nighttime appearance of the underside of a cloud layer over a city, caused by the reflection from the clouds of the city's lights; also called city blink.

Clammy: Descriptive of disagreeably moist, cool, calm air. Contrast humid: Descriptive of uncomfortably moist, warm or hot air.

Classification of clouds: Based upon the heights of their bases above ground, three general cloud types are recognized: low (stratus, cumulus); middle (altocumulus, altostratus); high (cirrus).

Clear: The state of the sky when there is a total absence of clouds, or when the presence of clouds is minimal and in no way dulls the sky or aspect of the day.

Clear air: Air that is devoid of clouds or fog; also, air that is so lacking in solid or liquid articles or pollutants that visibility through it is excellent -- often 50 miles or more.

Clear-air turbulence (CAT): In aviation terminology, bumpiness that is encountered by aircraft when flying through air devoid of clouds.

Clear sky: The state of the sky when clouds, if present at all, are inconspicuous: sunlight is not impeded during the day and stars are plainly visible at night.

Clear weather: The state of the weather when the atmosphere is very transparent (as opposed to foggy or hazy) and accompanied by negligible cloudiness.

Climate: The composite or generalization of all possible weather conditions at a location over a period of many years (by general agreement, 30 years), including such elements as temperature, humidity, wind, precipitation, cloudiness and their variations that, over short periods of time, constitute the weather at a specific location. .Two general climatic types are recognized: continental (the interiors of continents or land-influenced) and maritime (ocean-influenced).

Climate change: A major change (that is, having important economic, environmental and social effects) in the average values of atmospheric variables (like temperature) over a long period (a decade or longer).

Climatic controls: The relatively permanent factors that govern the climate of a region; those factors are (1) sunshine, (2) the distribution of land and water masses, (3) elevation and (4) ocean currents.

Climatic divide: A boundary between regions having different types of climate. The most effective climatic divides are the crests of mountain ranges. The crest of the Rocky Mountains separates the cloudy, rainy West Coast climate from the sunny, dry climate of the intermountain region.

Climatic Optimum: The period in history from about 5,000-2,500 B.C. during which temperatures were warmer than at present in nearly all parts of the Earth. A great retreat of glaciers and ice sheets occurred, the melt-water from which raised the sea level by about 10 feet.

Climatic uncertainty: The unknown ratio of the benefits and costs of climate change. Decision makers need to weigh and compare the risk of premature or unnecessary actions with the risk of failing to take actions that subsequently prove to be warranted.

Climatology: The study of the composite or generalization of all possible weather conditions at a location over a period of many years; the study of climate.

Climatotherapy: The treatment of disease or maintenance of good health by exposure to a suitable climatic environment.

Clog snow: A skiing term for wet, sticky new snow.

Close: Colloquially descriptive of oppressively warm, moist, still air that seems to threaten thunderstorms.

Closed upper low: A storm system in the upper atmosphere, generally above 15 thousand feet, about which the wind circulation (and consequently the height lines) forms a closed, nearly circular, loop. When viewed from above, wind circulation is counterclockwise. Ground-level weather is cloudy, windy, showery, unsettled.

Cloud: A visible collection of water droplets or ice particles suspended in the air at an elevation above the surface. A concentration of smoke or dust aloft is also considered to be a cloud.

Cloud bank: A fairly well-defined mass of cloud observed at a distance; it covers an appreciable portion of the horizon sky but does not extend overhead.

Cloud height: The height of the base of a cloud or cloud layer above the ground; the vertical distance between the base of a cloud or cloud layer and the ground. For cumulonimbus (the thunderhead), it's about 3,000 feet, whereas its top can extend to 65 thousand feet.

Cloud names: Most of the names given to clouds (cirrus, cumulus, stratus, nimbus, and their combinations) were coined in 1803 by the English meteorologist Luke Howard. He utilized Latin terminology for the names in his nomenclature.

Cloud seeding: Any technique carried out with the purpose of adding to a cloud certain particles that will alter the natural development of that cloud. The intent usually is to increase the amount of rain released from the cloud or to dissipate the cloud.

Cloud streets: Rows of cumulus or cumulus-type clouds aligned parallel to the low-level winds. Cloud streets sometimes can be seen from the ground, but are seen best on satellite photographs.

Cloud-to-ground lightning: A lightning bolt in which the original stroke jumps between a charge center in the cloud and some object on the ground. 95 percent of such flashes lower negative charge to the ground, 5 percent positive.

Cloudburst: An exceptionally intense rain, usually associated with thunderstorms. In hilly terrain, cloudbursts can result in devastating flash floods. Strictly speaking, this is not a meteorological term.

Clouds: A visible collection of water droplets or ice particles suspended in the air at an elevation above the surface. Concentrated smoke or dust aloft is also considered to be clouds.

Cloudy: The state of the sky when clouds predominate at the expense of sunlight by day or obscure the stars at night; completely cloud- covered, or there may be occasional small breaks in the cloud layer.

Cloudy sky: The state of the sky when clouds predominate at the expense of sunlight during the day or obscure the stars at night, but there may be occasional small breaks in the cloud layer.

Cloudy/overcast: The state of the sky when it is covered by clouds. Overcast: totally cloud-covered. Cloudy: cloud-covered, but there may be occasional small breaks in the cloud layer.

Clutter: Undesirable echoes on radar displays. On weather radars, clutter refers to echoes from ground targets (like trees, buildings, hills) near the radar site; also called ground clutter.

Coalescence: One of the processes which produces raindrops, it is the collision and resultant merger of two smaller cloud droplets into a larger droplet. Repetition of the process results in the formation of raindrops.

Cock-eyed bob: A colorful term used by old-timer residents of western Australia to refer to severe tropical cyclones and hurricanes, or to thunderstorms that are accompanied by very strong, gusty winds.

Cold: Having a low temperature, but not applicable during the summer. At a specific place, having a temperature decidedly below the normal for that place at that time of year. After the inception of the growing season, temperatures low enough to cause significant damage.

Cold-air funnel: A rotating funnel cloud that develops from the base of cumulus clouds or weak showers or thunderstorms when the air aloft is unusually cold. Usually weak and short-lived, they rarely touch down.

Cold front: (1) The transition zone between two air masses, one relatively cold and the other relatively warm, moving so that the colder air replaces the warmer air; the leading edge of a relatively cold air mass, and usually at the point of contact with the ground.

Cold front: (2) The boundary between two air masses, one relatively cold and the other relatively warm, moving so that the colder air replaces the warmer air; the leading edge of a relatively cold air mass.

Cold frontal passage: The movement across a location of the transition zone (cold front) between two air masses, one relatively cold and the other relatively warm, moving so that the colder air replaces the warmer air.

Cold pole: The location that has the lowest average annual temperature in its hemisphere. In the Northern Hemisphere the cold pole is usually placed at Verkhoiansk, Siberia, with an average annual temperature of +3 degrees Fahrenheit. Chicago's average annual temperature is 49 degrees; in the Southern Hemisphere it is probably Sovietskaya, Antarctica (-71 degrees F).

Cold rain: Steady and often wind-driven rain that falls when temperatures are in the 30s or 40s (or 50s in the spring). The sky is overcast, gray and dreary, and fog often accompanies wind-driven rain.

Cold sector: The area within the circulation of a low pressure system in which relatively cold air is located. This area usually lies behind the cold front associated with the low (that is, to the northwest of the low pressure center).

Cold soak: The effect of exposing mechanical equipment to very low temperatures for an extended period of time. Cold soak of engines necessitates preheating before their use because lubricants have thickened and metal has become brittle.

Cold Sunday: On Jan. 17, 1982, bitter cold prevailed from the Rockies to the Atlantic and Gulf coasts. Tower, Minn. -52 degrees F; International Falls -45; Milwaukee -26; Chicago -23; Buffalo -16; Washington D.C. -5; Montgomery, Ala. -5; Jackson Miss. -5.

Cold wave: In popular usage, a period of very cold weather. Meteorologically, a rapid fall in temperature within 24 hours to temperatures requiring substantially increased protection to agriculture, industry, commerce and social activities.

Colla: In the Philippines, a strong south to southwest wind (but generally no stronger than about 30 m.p.h.) accompanied by heavy rain and severe squalls; also known as colla tempestada.

Colorfastness: The ability of a substance to retain its original color under conditions of storage and exposure to environmental conditions. Exposure to sunlight is a usual cause of color fading.

Comet: Any of the possibly trillions of light-weight objects in prolonged orbit around the sun, ranging from about 1-25 miles in diameter, displaying eruptive activity that results in the formation of a tail spreading back from the sun as much as 200,000 miles.

Comfort zone: The ranges of indoor temperature, humidity and air movement under which most persons enjoy mental and physical well-being. The American Society of Heating and Air Conditioning Engineers gives limits of 67-80 degrees F. with a relative humidity of 30 percent.

Complex low: On a weather map, an area of low atmospheric pressure within which more than one low pressure center is found. A low pressure system usually contains only one well-defined low pressure center.

Condensation: In meteorological usage, the change of water vapor to liquid, as when fog or dew forms. The change from water vapor directly to ice, as when frost forms, is referred to as sublimation.

Condense: To change from water vapor to liquid, as when fog, dew or clouds form. The change from water vapor directly to ice, as when frost forms, is technically referred to as sublimation.

Cone of protection: The area below a lightning rod that is shielded from lightning. The radius of the protected horizontal distance is about two times the height of the object on which the rod is mounted.

Congelifraction: The cracking and splitting of rocks as a result of the freezing of the water contained in them; also called frost splitting.

Congeliturbation: The churning and stirring of soil as a result of repeated cycles of freezing and thawing. It includes such actions as frost heave and surface subsidence during thaws.

Continental climate: The climate that is characteristic of the interior of a land mass of continental size. It is marked by large annual, day-to-day and daily ranges of temperature. Chicago's climate is continental, slightly modified by its proximity to Lake Michigan.

Continental glacier: A continuous sheet of land ice that covers a very large area and moves outward in many directions, and so thick that it masks, even depresses, underlying land contours. The ice cap of Antarctica is an example.

Continentality: A measure of the extent to which the climate of a place is influenced by its distance from the oceans; the opposite of oceanicity. Chicago's climate is strongly continental, slightly modified by its proximity to Lake Michigan.

Contrails: Long, narrow, wispy cirrus-like clouds that form behind jet planes flying at high altitudes in below-freezing temperatures. They result from the condensation of water vapor remaining in jet exhaust.

Control day: A day on which the weather is supposed, according to folklore, to provide the key for the weather in a subsequent period. In the United States the best known of these days is Groundhog Day (Feb. 2).

Convection: The vertical movement, especially upward, of air--as in thunderstorms. Air rises when it is warmer, and consequently lighter, than the air around it. Convection is strongest in summer, weakest in winter.

Convective clouds: Clouds that owe their formation and vertical development to rising currents of warm air. Convective clouds, like cumulus, are the most numerous clouds in the summer sky.

Convective outlook: A forecast issued by the National Weather Service's Storm Prediction Center defining areas of expected thunderstorm occurrence and severity over the contiguous states.

Convergence: The flow of the wind resulting in a horizontal inflow of air into a region. Convergence at ground level requires that air immediately above the converging layer must rise. Convergence is the opposite of divergence.

Cool: In weather terminology, an adjective that gives a subjective description of a warm-season day (especially in the summer) whose temperature is expected to be well below the average temperature for that time of year. It is a term most appropriate to the warm season.

Cool change: In Australia, the passage of a vigorous cold front that breaks a summertime heat wave. It introduces cool, moist oceanic air that replaces intensely hot, dry continental air from the interior of Australia.

Cooler: When used in weather forecasts, a term indicating that temperatures are expected to be lower than 24 hours earlier, and usually by an appreciable amount. It is a term most appropriate to the warm season.

Cooling degree day: Calculated on a daily basis, it is the number of degrees that a day's average temperature is above 65 degrees. Each degree F.the daily average temperature (sum of the day's high and low temperatures, divided by 2) is above 65 degrees is one cooling degree day. A day whose average temperature is 75 degrees is said to have 10 cooling degree days.

Cooperative weather observer: An unpaid observer who maintains a weather observation station for the National Weather Service, which provides a maximum/minimum thermometer and a precipitation gauge.

Cordonazo: In Mexico, a local term for a tropical cyclone or hurricane in the Pacific Ocean off the nation's west coast.

Coriolis force: An apparent force that acts upon winds (and all other moving bodies). In the northern hemisphere, it acts to the perpendicularly to the right of the motion; for example, a wind from the north is deflected to the west.

Coriolis, Gaspard Gustave De: (1792-1843) The French engineer and mathematician who, in 1835, showed that the laws of motion may be used on a rotating frame of reference (like the Earth) if an inertia force is included in the equations. That inertia force came to be known as the Coriolis deflection.

Corn snow: Snow that has melted and refrozen into a rough, granular surface; also known as spring snow or granular snow.

Cornice: An overhanging structure of snow formed along mountain or ridge tops by wind-driven deposition of snow. Cornices are extremely hazardous to mountain climbers and can initiate avalanches. Also, overhanging snow on roofs, window ledges, etc., of buildings, especially prominent after a heavy snowstorm.

Corona: (1) A luminous circle around one of the heavenly bodies. More specifically, the irregular radial streams of light seen around the sun during a total eclipse.

Corona: (2) An atmospheric optical phenomenon which appears as prismatic colored ring of small radius, concentrically surrounding the sun, moon or other luminous object when they are veiled by a thin cloud consisting of water droplets; also, the radial streams of light seen around the sun during a total eclipse.

Cosmic abundance: By weight, hydrogen accounts for about 73 percent of all the material in the Solar System, helium accounts for 25 percent and all other materials total only 2 percent.

Cosmic winter: Severe global cooling following the impact of a large comet or asteroid on the Earth. The scenario envisions a chilled Earth enshrouded for months or years in smoke and dust.

Cosmology: The study of the large-scale structure of the universe. It is concerned with fundamental questions about the formation, evolution and future development of the universe.

Crawler lightning: A slang term for cloud-to-cloud lightning that spreads or crawls across the sky. For sky watchers, this kind of lightning produces some of the most spectacular light shows.

Crepuscular rays: In the atmosphere at or shortly before or after sunset, the alternating lighter and darker bands (rays and shadows) across the western sky which appear to diverge in fan-like array from the position (below the horizon) of the sun. Crepuscular rays are made visible by haze in the atmosphere.

Cricket thermometers: Air temperature greatly influences the rate that crickets chirp. The temperature may be quite accurately determined by counting the number of cricket chirps in 14 seconds and then adding 40.

Crud: In sports, a colloquial term for heavy, sticky snow that is unsuitable for skiing.

Cryology: The study of the physical properties of ice, snow, sleet, hail and all other forms of water substance whose temperature is below freezing; also, the study of sea ice.

Cryopedology: The study of ground movement caused by intensive frost action or permafrost, their causes and occurrences, and the engineering devices and practices devised to overcome difficulties caused by them.

Cryophobia: The irrational or morbid fear of ice, ice storms, blizzards.

Cryosphere: The portions of the Earth (in the atmosphere, at the surface and in the ground) in which water is in solid form. It includes below-freezing air and snow, sleet, and hail in the air, snow and ice on the ground, glaciers, ice fields, and icecaps, frozen soil (permafrost) and floating ice (on oceans, lakes, rivers, etc.) The word is derived from the Greek kyros, meaning frost or icy cold.

CST (Central Standard Time): In the autumn, the change from Central Daylight Time (CDT) to CST is accomplished at 2:00 a.m CDT by turning the clock back one hour to 1:00 a.m.CST. In the spring, the change from CST to CDT is accomplished at 2:00 a.m.CST by turning the clock ahead one hour to 3:00 a.m. CDT. The result of the change is that in the autumn the sun rises and sets one hour earlier; in the spring, the sun rises and sets one hour later.

Cu: (pronounced like the letter Q): Weather jargon for cumulus clouds, the isolated, flat-bottomed, puffy dob-of-cotton clouds that populate the skies in the summer.

Cumuliform: Descriptive of clouds of extensive vertical development, as contrasted to horizontally-developed stratiform cloud types. Cumuliform clouds predominate during the summer in climates like Chicago's.

Cumulonimbus: The thunderhead, the dense and vertically-developed cloud that produces thunderstorms. The top is often anvil-shaped and flat. The cloud can bring heavy showers, hail, lightning and high winds, sometimes tornadoes, and typically reaches to elevations of 35 to 60 thousand feet.

Cumulonimbus mamma: A supplementary cloud feature in the form of hanging protuberances, like pouches, on the under side of the anvil of cumulonimbus (thunderhead) clouds. It is not associated with tornadoes.

Cumulus clouds: Clouds in the form of individual, detached elements. Flat-bottomed, resembling piles of cotton, they grow vertically, appearing as mounds or towers with upper portions resembling cauliflower; especially prevalent during warm-season afternoons.

Cumulus congestus: A cumulus cloud whose vertical height greatly exceeds its width, with a distinctive cauliflower top but lacking the cumulonimbus anvil; might or might not produce a shower.

Cumulus humilis clouds: The isolated, puffy, flat-bottomed dob-of-cotton clouds that dot our summertime skies during fair afternoons. They form when bubbles of warm air rise to the level of condensation and they are the most common clouds in summer.

Cunette: A longitudinal channel constructed along the center or lowest part of a channel or through a detention or retention pond and intended to carry low flows; also known as a trickle channel.

Cutoff low: An upper low pressure system that is displaced from and lies to the south of the basic westerly current. It occupies the core of an upper cold air mass, often is stationary, and usually produces inclement weather at ground level.

Cyclogenesis: The first appearance of a low-pressure system or low-pressure trough in the atmosphere, or the strengthening of an existing low or trough; the opposite of cyclolysis.

Cyclolysis: The weakening or disappearance of a low pressure system or low pressure trough in the atmosphere; the opposite of cyclogenesis.

Cyclone: In meteorology, a low pressure system. When viewed from above, wind circulation is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. In popular usage, it is a term variously applied to tornadoes, waterspouts, dust storms, hurricanes and even to any strong wind.

Cyclonic rotation: Rotation about a vertical axis in the same direction as the Earth's rotation. When viewed from above, it is counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere.

Cyclonic storm: Cyclonic storm: A low pressure system; a large (100+ miles in diameter) area of low pressure whose winds (in the Northern Hemisphere) spiral inward in counterclockwise fashion when viewed from above.