Weather map 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. The use of weather charts in a modern sense began in the middle portion of the
NOAA Weather Radio broadcast routine segment if no report is available from the main reporting station, in which case the substituted station's observations will not be repeated at the end of the segment. In some locales, in the event any weather reporting station (whether the main station or a distant site) whose condition reports are regularly included in the segment had absent data, or no data available, the following message would be played in its place:In some areas, a major city featured within the regional observations would always provide weather conditions; if a condition report is unavailable, the message "the weather conditions were not available"