It is quite absurd to report on a future event, isn't it? One can report on a prediction, but not the future event itself. Isn't it better to say, "The weather forecast says that it will rain tomorrow"? If you want to be rigorous, which I think all learners should be, the rules are: Predictions: use simple future tense - It will rain tomorrow. Intentions: use "going to" - We are going to get married next year.

Hi Victoria, "It will" and "is going to" are statements used to make predictions and are interchangeable. Hope this helps! Ed

Both are correct. "Is going to" is simply more casual; something you would say in conversation.