Weather forecasting depends on collecting facts about the state of the air. Ground stations, balloons, ships and satellites measure temperature, humidity, wind speed and air pressure. These numbers go into powerful computers. The computers simulate the movement of air by the laws of physics. Then they show the chances of different weather in the coming days. Near forecasts, such as tomorrow's weather, are more exact than far ones. This is because small errors in measurement grow as time passes. For this reason, weather reports update their forecasts several times a day. These forecasts help farmers, pilots and sailors. They also warn people of storms before the storms arrive. Official bodies publish these warnings on television and in apps.

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