weather, state of the atmosphere at a given time and place with regard to temperature, air pressure (see barometer barometer (bərŏm`ətər), instrument for measuring atmospheric pressure.
..... Click the link for more information. ), wind, humidity, cloudiness, and precipitation. The term weather is restricted to conditions over short periods of time; conditions over long periods, generally at least 30–50 years, are referred to as climate climate, average condition of the atmosphere near the earth's surface over a long period of time, taking into account temperature, precipitation (see rain ), humidity , wind , barometric pressure, and other phenomena.
..... Click the link for more information. .

The earliest evidence of scientific activity in the field of meteorology meteorology, branch of science that deals with the atmosphere of a planet, particularly that of the earth, the most important application of which is the analysis and prediction of weather .
..... Click the link for more information. , the study of the earth's atmosphere, especially as it relates to weather forecasting, is from the 4th cent. B.C.; Aristotle wrote what is probably the first treatise on the subject. The first attempt to chart weather from reports over a considerable area was made (1820) in Europe by H. W. Brandes, but it was not until after the invention of the telegraph that the rapid collection of weather data from remote stations became possible.

In the United States, a government weather service was established (1870) under the army Signal Corps. In 1891 the weather service was transferred to the U.S. Weather Bureau under the Dept. of Agriculture, and it later came (1940) under the jurisdiction of the Dept. of Commerce. The U.S. Weather Bureau has since been renamed the U.S. National Weather Service and transferred to the National Oceanic and Atmospheric Administration. The central forecast office is the National Meteorological Center (NMC), in Suitland, Md.; first-order stations are located chiefly in the larger cities, and numerous substations for special purposes (e.g., observing river stages, measuring depth of snow, and maintaining records of climate) are distributed throughout the country.

Devices used for meteorological observations include rockets, weather satellites, radiosondes radiosonde (rā`dēōsŏnd)
..... Click the link for more information. , barometers, anemometers, weather vanes weather vane or wind vane, instrument used to indicate wind direction. It consists of an asymmetrically shaped object, e.g., an arrow or a rooster, mounted at its center of gravity so it can move freely about a vertical axis.
..... Click the link for more information. , psychrometers psychrometer (sīkrŏm`ĭtər)
..... Click the link for more information. , thermometers thermometer, instrument for measuring temperature . Galileo and Sanctorius devised thermometers consisting essentially of a bulb with a tubular projection, the open end of which was immersed in a liquid.
..... Click the link for more information. , and radar radar, system or technique for detecting the position, movement, and nature of a remote object by means of radio waves reflected from its surface. Although most radar units use microwave frequencies, the principle of radar is not confined to any particular frequency
..... Click the link for more information. . By means of high-speed telecommunications, information from all over the world is sent to the NMC, where the data is decoded and plotted. These data are used to create weather maps based on simultaneous weather observations at different atmospheric levels over any desired geographic region. On a typical map the various weather elements are shown by figures and symbols; isobars isobar (ī`səbär') or isobaric line
..... Click the link for more information. are drawn to show areas of low pressure (cyclones cyclone, atmospheric pressure distribution in which there is a low central pressure relative to the surrounding pressure. The resulting pressure gradient, combined with the Coriolis effect , causes air to circulate about the core of lowest pressure in a
..... Click the link for more information. ) and high pressure (anticyclones); fronts front, in meteorology, zone of transition between adjacent air masses . If a cold air mass is advancing to replace a warmer one, their mutual boundary is termed a cold front; if the reverse, then the boundary is termed a warm front, whereas a stationary front
..... Click the link for more information. (boundaries between air masses air mass, large body of air within the earth's atmosphere in which temperature and humidity, although varying at different heights, remain similar throughout the body at any one height.
..... Click the link for more information. ) and areas of precipitation are indicated.

By using computer models based on mathematical formulations of the dynamics of the atmosphere, weather charts are also produced as prognostics of future weather patterns. The many simplifying assumptions required in these formulations, as well as the incompleteness of weather data, limit the accuracy of the computer predictions; though as advances in computer systems occur, these models are becoming more complete and, hence, more accurate. Meteorologists interpret and modify such prognostics according to their knowledge of the prognostics' reliability and their familiarity with local influences, such as topography and proximity to large bodies of water, in order to derive the best possible weather forecasts.

Forecasts are disseminated by television, radio, telephone, newspapers, and the Internet. Detailed forecasts can usually be made only for a short future period (generally 48 hr or less). Forecasts for up to five days can usually predict departures from normal temperature and precipitation fairly well; longer-range predictions are more general and less accurate, being based on the known normal weather of the area. Mathematical models, particularly those run on supercomputers, have helped to understand weather changes, including general global circulation patterns, and how perturbations in the atmosphere and oceans effect the weather.

Bibliography

See J. R. Eagleman, Weather Concepts and Terminology (1989); J. Farrand, Jr., Weather (1990); H. M. Conway and L. L. Liston, Weather Handbook (1990); R. C. McNeill, Understanding the Weather (1991).

weather

State of the atmosphere at a particular place during a short period of time. It involves day-to-day changes in such atmospheric phenomena as temperature, humidity, precipitation (type and amount), air pressure, wind, and cloud cover. Most weather occurs in the troposphere, but phenomena of the higher regions of the atmosphere, such as jet streams, and geographic features, most notably mountains and large bodies of water, also affect it. See also climate.

weather (redirected from making heavy weather)

Bibliography

weather

weather
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