\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.