Question: how do the weather people no what the weather is when the day has not com ?

Joe Sweeney answered on 10 Mar 2014:

Now THAT is a smart question. Weather forecasters make their guesses (remember, that’s what they are: educated guesses, which are often wrong!) by looking at satellite pictures of clouds and other weather features. They track the movement of the weather features over a period of days, and this makes them confident about predicting what’s going to happen in the future. They can tell (based on knowing what has happened before) what types of clouds will lead to what type of weather. They can also tell where strong winds are, are where they will blow over the next few days. However, its not possible to be 100% accurate, because there are many, many things which control weather and if they change quickly, the forecasters can be left looking silly!