Weather is the instantaneous or current state of the atmosphere. It is characterised by a range of atmospheric parameters such as temperature, pressure, humidity, wind speed and direction, cloudiness and precipitation (e.g. rain).
Weather parameters are measured with different instruments. For instance, atmospheric temperature and pressure are typically measured with a thermometer and a barometer.
In general, the weather that impacts the surface of the Earth and the people that live on it takes place in the troposphere.
The figure shows an example of weather satellite map for the 27th of September 2010 at 2pm. Clouds appear in white. This type of weather map is used to test model weather forecasts.