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
Weather warning [increasing] significantly, but its occurrence, location, and/or timing is still uncertain"" and a warning as ""hazardous weather or hydrologic event [that] is occurring, is imminent, or has a very high probability of occurring"" . Additionally, the NWS breaks down weather warnings and watches based upon the specific type of hazardous weather. These warnings and watches include, but are not limited to, flooding, severe local storms, tropical cyclones, and winter storms. In Canada, governmental weather warnings and watches are issued by the Environment Canada. Non-governmental alerts, not watches or warnings, such as a "rotation detected" or "tornado reported" are issued by