What is "weather map"

Weather map \Weath"er map\ A map or chart showing the principal meteorological elements at a given hour and over an extended region. Such maps usually show the height of the barometer, the temperature of the air, the relative humidity, the state of the weather, and the direction and velocity of the wind. Isobars and isotherms outline the general distribution of temperature and pressure, while shaded areas indicate the sections over which rain has just fallen. Other lines inclose areas where the temperature has fallen or risen markedly. In tabular form are shown changes of pressure and of temperature, maximum and minimum temperatures, and total rain for each weather station since the last issue, usually 12 hours.

n. a map that shows the analysis of meteorological quantities at various levels of the atmosphere

n. a map showing the principal meteorological elements at a given time and over an extended region [syn: weather chart]

A weather map displays various meteorological features across a particular area at a particular point in time and has various symbols which all have specific meanings. Such maps have been in use since the mid-19th century and are used for research and weather forecasting purposes. Maps using isotherms show temperature gradients, which can help locate weather fronts. Isotach maps, analyzing lines of equal wind speed, on a constant pressure surface of 300 mb or 250 mb show where the jet stream is located. Use of constant pressure charts at the 700 and 500 hPa level can indicate tropical cyclone motion. Two-dimensional streamlines based on wind speeds at various levels show areas of convergence and divergence in the wind field, which are helpful in determining the location of features within the wind pattern. A popular type of surface weather map is the surface weather analysis, which plots isobars to depict areas of high pressure and low pressure. Cloud codes are translated into symbols and plotted on these maps along with other meteorological data that are included in synoptic reports sent by professionally trained observers.