We use the special going to construction when we have the intention to do something before we speak. We have already made a decision before speaking. Look at these examples:
In these examples, we had an intention or plan before speaking. The decision was made before we spoke.
We often use going to to make a prediction about the future. Our prediction is based on evidence. We are saying what seems sure to happen. Here are some examples:
In these examples, the present situation (black sky/the time/damaged car) gives us a good idea of what is going to happen.