We use will to make predictions about the future when we are certain that something is going to happen.

We use be going to when our prediction is based on a present situation or evidence.

We use might to show future posibility.

We use be likely to when we think something will happen, but we are not certain.

http://www.bbc.co.uk/learningenglish/english/course/lower-intermediate/unit-28/session-2/activity-3