Weather Words - T

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10-year storm: A storm (or other event, such as a flood) that has an annual probability of occurrence of 1/10. When it occurs in a given year, its likelihood of happening again in the next near is still 1/10. Tacoma-Narrows Bridge collapse: Nicknamed "Galloping Gertie," the huge suspension bridge spanning Puget Sound at Tacoma, Washington, collapsed on November 7, 1940, four months after opening. Evenly-spaced spans of the bridge swayed with increasing amplitude in strong winds, leading to the collapse.

Tail-end charlie: (slang) The thunderstorm at the southernmost end of a squall line of thunderstorms. Since warm moist inflow into such a storm is relatively unimpeded, it is the most likely storm to become severe.

Tailwind: A wind blowing in the same direction as that of an object (such as an airplane) moving through the air; the opposite of a headwind.

Talik: Permanently unfrozen ground in regions of permafrost.

Teeth of the gale: An old nautical term for the direction from which the wind is blowing. To sail into the "teeth of the gale" or into the "eye of the wind" is to sail into the wind.

Teleconnection: A strong statistical relationship between weather in different parts of the Earth. For example, a teleconnection exists between tropical and North American weather during El Niño.

Teletsunami: A tsunami (an ocean wave produced by a submarine earthquake, landslide, or volcanic eruption) that can cause damage far away from its source.

Temperate: Moderate; not excessive. Climatologists define the Earth's temperate zones to be the two planet-encircling belts that lie between the hot, wet tropics and the cold, dry polar regions.

Temperate climate: The climate of the "middle" latitudes. (1) The variable climate between the extremes of the belt of hotter, wetter tropical climates in equatorial regions and the colder, drier polar climates to the north. (2) A climate with distinct summer and winter seasons, located in an Earth-circling belt between the extremes of tropical and polar climates. (3) The climate of the "middle" latitudes. A climate with distinct summer and winter seasons, located in two Earth-circling belts between the extremes of tropical and polar climates.

Temperate rainforest: Lush forests growing in regions of high precipitation in mid (even high) latitudes, such as the North Pacific coastal rainforests that extend from Oregon to Alaska.

Temperature: (1) A measure of the "hotness" or "coldness" of a substance; in thermodynamics, a measure of the energy of "vibrational" molecular motion of a substance, higher temperatures being associated with greater molecular motion. (2) The thermal state of a body considered with reference to its ability to transfer heat to other bodies. The body losing heat is defined as having a higher temperature, the body receiving it as having a lower temperature.

Terminal fall speed: The particular falling speed of a precipitation particle at which drag and buoyant forces on the particle just equal the gravitational force on the particle, after which it falls at a constant speed.

Terminator: When viewed from space, the distinct boundary between the illuminated (daylight) and dark (night) areas of the full disk image of the Earth.

Thaw: A spell of mild weather during the winter sufficiently warm to cause snow and ice to melt; to change from ice to water by gradual warming; to change from a frozen to unfrozen state, as when soil thaws.

The Dry: In tropical northern Australia, the winter dry season during which practically no rain falls. It extends from May into October.

The Wet: In tropical northern Australia, the summer monsoon season during which heavy rain falls, extending from November into April. It is approximately coincident with winter in the Northern Hemisphere.

Theodoric: (1250-1310) German Dominican monk, the first to explain (in 1304) that rainbows are caused by raindrops. Using a water-filled glass globe, he showed that sunlight can be split into a rainbow's colors.

Thermal: (1) A bubble or small-scale current of rising air, warmer and therefore more buoyant than its immediate surroundings. The term is usually used to denote currents too small or too dry to produce cumulus clouds. (2) A transient bubble or small-scale current of rising air.

Thermal low: (also called heat low) An area of low pressure resulting from intense heating and high temperatures. It is stationary and its wind circulation is weak. A thermal low forms over Arizona in summer.

Thermal pulse: The intense burst of heat and light released by a nuclear explosion, and one of the most destructive effects of the explosion; also called nuclear flash.

Thermocline: In a lake or ocean, the relatively sharp thermal boundary between warmer water above and cooler water below. Lake Michigan's permanent thermocline lies at the top of the deep-lake water that remains at 39° through the year.

Thermograph: A recording thermometer; that is, a weather instrument which measures air temperature and makes a continuous line graph of the values.

Thermometer: An instrument that measures temperature by utilizing the changes of the physical properties of a substance when its temperature changes (expansion or contraction of mercury or alcohol, for example).

Thermophobia: The irrational fear of heat or high temperatures.

Thoron: A radioactive gas that exists briefly in trace amounts in the atmosphere only within about 35 feet of the ground as a result of seepage from soil and rocks. Its half-life is about 55 seconds.

Thule Air Force Base wind: On March 8, 1972, Thule Air Force Base in Greenland reported a wind gust of 207 m.p.h. The world's highest measured wind speed is a 231 m.p.h. gust on April 12, 1934, at Mt. Washington, N.H.

Thunder: (1) The sharp or rolling sounds resulting from lightning discharges. A lightning spark can heat the air to 54,000 degrees Fahrenheit. Such extreme heating causes air to expand explosively, initiating a shock wave that we hear as thunder. (2) Sound waves move through the atmosphere at a speed of 720 m.p.h., or one mile in five seconds. To obtain the distance in miles of a lightning bolt, divide by 5 the number of seconds between flash and thunder. (3) Thunder: The sound generated by lightning. It is rarely heard beyond 15 miles from the lightning discharge, and 25 miles is an approximate extreme upper limit of audibility. (4) A lightning spark can heat the air to 54,000 degrees Fahrenheit. Such extreme heating causes air to expand explosively, initiating a shock wave that we hear as thunder.

Thunder, audible range of: The sound of thunder usually travels no more than about 10 miles, but the audible range can be much less if the sound passes through heavy rain.

Thunderbolt: In mythology, a lightning flash accompanied by a material "bolt" or dart; this is the legendary cause of the damage done by lightning. The term is still used as a popular term for a lightning discharge accompanied by thunder.

Thunderhead: The popular term for the huge cloud tower, especially when viewed from a distance, of a cumulonimbus cloud, the cloud that produces thunderstorms.

Thundersnow: A colloquial term that first came into use in the 1970s for any thunderstorm with snow; that is, snow accompanied by lightning and thunder. When thunderstorms produce snow, the rate of snow accumulation is often extreme-- 3-6 inches per hour.

Thundersquall: The combined occurrence of a thunderstorm and a squall, the squall being associated with the outrush of air in a well-developed thunderstorm.

Thunderstorm: (1) A local storm produced by a cumulonimbus cloud and always accompanied by lightning and thunder (the defining characteristics). Rain, hail and high winds may or may not be present. (2) A storm that produces lightning. Worldwide, about two thousand thunderstorms are in progress at any given moment; 45 thousand thunderstorms occur daily and 16 million annually. (3) A local storm that produces lightning (the defining and necessary characteristic). Thunder, rain, hail and high winds may or may not be present.

Thunderstorm daily frequency: About 40,000 thunderstorms occur each day on the planet, and most are in equatorial regions. Thunderstorms occur most frequently over land, but do occur over the oceans as well.

Thunderstorm energy: A single thunderstorm can release 125 million gallons of water and discharge enough heat to supply the entire United States with electric power for 15 minutes. A large hurricane will multiply those values an incredible 12,000 times.

Thunderstorm frequency: (1) Worldwide, about 2,000 thunderstorms are occurring at any given moment. About 100,000 thunderstorms occur per year in the United States, and ten percent of them are severe. (2) Worldwide, about 2,000 thunderstorms are in progress at any given moment; 40-45 thousand thunderstorms occur daily, 16 million annually.

Thunderstorm hazards: Thunderstorms are "weather factories" that can bring five kinds of hazardous weather: lightning, large hail, high straight-line winds, tornadoes and flash-flood producing rains.

Tidal wave: In popular usage, any unusually rapid and high (and therefore destructive) rise of water along a seashore, caused by underwater earthquakes, volcanoes or landslides. Note: Its cause has nothing to do with tides.

Tide: The regular rise and fall of the Earth's oceans caused by the actions of the moon's and sun's gravitation acting on the rotating Earth.

Time-release rain: A colloquial reference by residents of northern Wisconsin and Upper Michigan to snow that occurs after March 31.

Tokyo earthquake: On Sept. 1, 1923, one of the world's greatest quakes struck Tokyo, Japan. The final death toll, 140,000, resulted mainly from massive fires that swept the city after the earthquake.

Tonitrophobia: The irrational or morbid fear of thunder.

Topography: The lay-out of major natural and man-made physical features of the Earth's surface. Mountains, rivers, bridges, highways, trees and fields are all components that make up topography.

Tornado: (1) A violently rotating column of air extending downward from the base of a cumulonimbus cloud (thunderhead) and making contact with the ground. Highest tornadic winds are about 315 mph. (2) A violently rotating column of air extending from the base of a thunderstorm to the ground. The air within a tornado spirals upward in corkscrew fashion, with top speeds of about 318 mph. (3) A violently rotating column of air extending from the base of a thunderstorm down to the ground. It is made visible by condensation of water vapor and by dust and debris carried aloft by the wind.

Tornado alley: That portion of the United States in which tornadoes occur most frequently, encompassing the Plains area between the Rocky Mountains on the west and the Appalachians on the east.

Tornado deaths: Mobile homes are dangerous places to be during a tornado. In the United States, about 50 percent of tornado deaths are attributed to mobile homes.

Tornado fact: About 20 (or 2 percent) of the 1000+ tornadoes that strike the United States each year contain winds of 200 m.p.h. or higher.

Tornado outbreak: Multiple tornado occurrences, usually ten or more, associated with a particular weather system (usually a low pressure system) as it moves across the country.

Tornado outbreak of April 3-4, 1974: Greatest in U.S. history: 148 separate tornadoes, including 48 killer tornadoes (315 fatalities) and 30 tornadoes reaching F4 or F5 intensity. The first tornado in this outbreak touched down near Morris, Ill.

Tornado season: Tornadoes occur in all seasons of the year in the United States, but spring and summer are the seasons of greatest frequency. In Illinois, tornado season is March, April, May, June.

Tornado strength categories: Weak, winds 40-112 m.p.h. (F0 and F1 on the Fujita tornado F-scale); strong, winds 113-206 m.p.h. (F2 and F3); violent, winds 207-318 m.p.h. (F4 and F5).

Tornado wind categories: F0: winds 40-72 m.p.h.; F1: 73-112 m.p.h.; F2: 113-157 m.p.h.; F3: 158-206 m.p.h.; F4: 207-260 m.p.h.; F5: 261-318 m.p.h.

Torricelli, Evangelista: (1607-1647) The inventor of the barometer. Because water would rise only 32 feet in a suction tube, he deduced that air had weight and could, therefore, exert a definite pressure.

Tourist repellent: In New England, a reference to rain that falls during the height of the summertime tourist season.

Towering cumulus: A cumulus cloud whose vertical height considerably exceeds its width, with a distinctive cauliflower top but lacking the characteristic anvil of cumulonimbus (the thunderhead).

Tower of the Winds: An octagonal, marble building in Athens, Greece, erected before 35 BC and still standing. The eight sides face the points of the Athenian compass and each side carries a frieze of the male personification of the wind from that direction (N, NE, E, SE, S, SW, W, NW).

Trace of precipitation: For liquid precipitation, an amount less than 0.005 inch; for frozen precipitation, melted water content less than 0.005 inch. Dew and frost are not considered to be precipitation.

Trade winds: Winds which blow from tropical high pressure belts toward the equatorial region of low pressure; from the northeast in the northern hemisphere, from the southeast in the southern hemisphere.

Training: The repeated occurrence of thunderstorms at a specific spot because the motion of individual thunderstorms oriented in a line is approximately along the line rather than at an angle to it.

Translucidus: A cloud variety occurring in a layer or extensive sheet, the greater part of which is sufficiently thin and translucent to reveal the position of the sun or (at night) the moon.

Transpiration: The process by which water in plants moves through leaf pores and is released into the atmosphere as water vapor. Actively growing plants release so much water vapor that dry air masses are steadily moistened.

Trinity Test: Code name for the detonation of the world's first nuclear device. The detonation was conducted by the United States government near Alamogordo, New Mexico, on July 16, 1945.

Tri-state tornado: On March 18, 1925, the largest, longest, fastest, most destructive and most deadly tornado in U.S. history, the Great Tri-State Tornado, cut a 219-mile path from southeast Missouri across southern Illinois into southwest Indiana; 695 people died, at least 2,000 were injured. In all respects, this remarkable tornado stands in a class of its own.

Tropical air: Air whose characteristics are developed at low latitudes. Maritime tropical air, warm and humid, forms over tropical and subtropical seas. Continental tropical air, hot and dry, forms over tropical deserts.

Tropical cyclone: (1) A low pressure system in the tropics or subtropics, classified by highest sustained winds: disturbance, no organized winds; depression 38 mph or less; storm 39-73 mph; hurricane 74 m.p.h. or higher. (2) A low pressure disturbance (cyclone) that forms over warm tropical or subtropical waters, classified (in the United States) according to its highest sustained wind speeds: tropical depression, 38 m.p.h. or less; tropical storm 39-73 m.p.h.; hurricane 74 m.p.h. or greater. (3) The generic term for a low pressure system, not associated with fronts, over tropical or sub-tropical waters, and with precipitation organized in counterclockwise-curving spiral bands.

Tropical cyclones: (1) Low pressure systems that form over tropical oceans, classified according to their highest sustained wind speeds. Tropical depression: up to 38 m.p.h.; tropical storm: 39-73 m.p.h.; hurricane: 74 m.p.h. and higher. Tropical cyclones, average annual number worldwide: Tropical storms (wind 39+ m.p.h.) 88; hurricane (74+ m.p.h.) 48; severe hurricane (111+ m.p.h.) 21.

Tropical depression: A cyclonic (low pressure) circulation which develops over warm tropical or sub-tropical ocean waters and produces sustained winds no higher than 38 m.p.h.

Tropical disturbance: (1) A poorly organized area of low pressure which develops over warm tropical ocean waters. There may be gusty winds associated with scattered thunderstorms, but tropical disturbances bring little or no organized wind. (2) A poorly organized area of low pressure over warm tropical or sub-tropical ocean waters, with little or no organized wind circulation other than gusty winds in scattered showers/thunderstorms.

Tropical rainfall: Rainfall in most areas of the tropics is very heavy, and about two-thirds of all the precipitation that falls on the entire planet occurs in the tropics.

Tropical storm: (1) A strong cyclonic (low pressure) circulation that develops over warm tropical ocean waters and produces sustained winds of 39-73 m.p.h.; known as a hurricane when winds are 74 m.p.h. or greater. (2) A cyclonic (low pressure) circulation that contains sustained winds of 39-73 m.p.h.; known as a hurricane when winds are 74 m.p.h. or greater.

Tropics: The region of the Earth located between the Tropic of Cancer at 23.5 degrees North latitude and the Tropic of Capricorn at 23.5 degrees South latitude. It encompasses a region with continually high temperatures and considerable precipitation, at least during part of the year.

Tropopause: Varying between 4 miles at the Earth's poles and 12 miles at the Equator, it is the "top" of the troposphere (the lowest layer of the atmosphere -- the layer in which "weather" occurs).

Troposphere: (1) The lowest layer of the atmosphere, extending from the Earth's surface upward to a height of 4-12 miles. Temperatures decrease with height, and it is the layer in which "weather" occurs. (2) Troposphere: The lowest layer of the atmosphere, extending from the Earth's surface upward to a height of 4-10 miles. In the troposphere, temperatures decrease with increasing height, and it is the layer in which "weather" occurs.

Tropospheric ozone: Ozone that occurs near the surface of the Earth. It is a pollutant of concern in smog because of its toxic effects. Ozone occurs naturally in the upper atmosphere about 10-15 miles above the surface.

Trough: (1) An elongated area of low air pressure, often several hundred miles in length, containing no low pressure center and therefore no closed isobars. The term is used to distinguish from a low pressure system containing a center around which there is at least one closed isobar. (2) An elongated U-shaped area of low air pressure, often several hundred miles in length, containing no low pressure center and therefore no closed isobars. (3) An elongated U-shaped area of low air pressure, often several hundred miles in length, containing no low pressure center and therefore no closed isobars, and often a source of active weather.

Tsunami: (1) An ocean wave produced by a submarine earthquake, landslide, or volcanic eruption. Only a few inches high in the open ocean, tsunamis steepen and rise in shallow water and can reach heights of 200 feet. Tsunami means "harbor wave" in Japanese. (2) Four of five occur in the Pacific Ocean. Hawaii has been hit by five tsunamis in the past 100 years; 14 on the California coasts (where they are known as "unsurfable waves") since the early 1800s.

Tsunami frequency: On average, one destructive tsunami occurs in the Pacific basin about every seven years, but (as of 2005) there has been none in over 30 years. Tsunami means "harbor wave" in Japanese.

Tsunami warning centers: The U.S. National Weather Service operates two tsunami warning centers for the Pacific Ocean: The Pacific Tsunami Warning Center located in Ewa Beach, Hawaii, and the West Coast and Alaska Tsunami Warning Center in Palmer, Alaska.

Tsunamis: Sea waves (incorrectly called tidal waves) caused generally by earthquakes, less commonly by submarine landslides, infrequently by submarine volcanic eruptions and very rarely by large meteorite impacts in the ocean.

Tucson, Ariz., snowstorm: Tucson, among the ten hottest cities in the United States and located in the Sonoran Desert, received 6.4 inches on snow on November 16, 1958.

Tule fog: Ground fog in California's Central Valley, and the leading cause of weather-related deaths in that state (resulting from chain-reaction, multiple-vehicle highway accidents).

Tundra: Treeless plains which lie to the north of the "tree line". The vegetation consists of sedges, mosses, lichens, a few shrubs. Because it is mostly underlain by permafrost, drainage is poor and the soil is often saturated.

Tunguska airburst: At 7:30 a.m., June 30, 1908, an asteroid disintegrated five miles above the Tunguska area of eastern Siberia. The blast flattened about 1,000 square miles of uninhabited forest.

Turbulence: The irregular motion which appears in liquid or gaseous fluids when they flow past solid surfaces or when neighboring streams flow past or over each other. Near the surface, the Earth's atmosphere exhibits turbulent motion.

Twilight: The interval of incomplete darkness before sunrise (morning twilight) and after sunset (evening twilight). The duration of the twilight period varies considerably with distance from the equator and the calendar date.

Twister: In the United States, a popular and non-technical term for a tornado.

Typhoon: A hurricane of the western Pacific Ocean. The origin of the word is derived either from the Cantonese t'ai fung ("great wind"), from the Arabic tufan ("smoke"), or from the Greek typhon (monster).