How weather forecasts are created

There are three important stages to a weather forecast:

  1. Knowing what the weather is doing now
  2. Calculating how this will change in future
  3. Using meteorological expertise to refine the details

In order to know what the weather will do in the future, we first need to know accurately what it is doing now. Recordings of weather variables are made 24 hours a day across the globe. These are passed to the world's major weather forecasting centres and used in conjunction with satellite pictures to get a picture of what the atmosphere is doing now. These are called observations. 

The weather forecasting centres have huge supercomputers, which use these observations as ‘starting conditions’ for very complex equations which can predict where the weather will move, and how it will evolve as time goes on. 

The computer models are run several times a day, and meteorologists work around the clock to check that the forecast is going to plan. If it is not, they will amend any forecasts going out to customers, if that change affects their operations. For example, if the temperature is slightly lower than expected that can mean the difference between frost or not by the end of the night, and whether a lorry needs to go out and grit a road.