Ancient dream interpretation can be a very strange thing, as ancient Egyptian dream manuals seem mostly opaque. The final verses of the Septuagint version of the book of Esther provide an interpretation of Mordecai's dream from the initial chapter of Esther. What is interesting about the interpretation is that Mordecai is finally able to interpret his enigmatic dream after the events have already occurred.
Prophecy is often like that. The prophecy is often not so much post hoc (or after the fact) as the interpretation is. Often only after things have happened are we able to figure out that God had warned us of them beforehand, but we were too busy paying attention to the wrong things.