Let me answer that with a question:

If Almighty God knows that something terrible is going to happen, is there any chance that it won't?

If the answer is yes, then He is not, in fact, all knowing. Either He has to intervene in a situation He did not intend or anticipate, or He was unable or unwilling to intervene in a situation He did not intend or anticipate, or else He did intend for it to happen and planned, from eternity, for it happen (because He lives outside of linear time). Only the latter option can possibly be true, since He is all mighty, all knowing, and eternal. Unless we're talking about some "lesser" god than the God of the Scriptures.

This isn't just a matter of "Reformed" or "non-Reformed" belief. It is how one views God - either as the Almighty, eternal Sovereign of the universe or some lesser being who doesn't get his way most of the time.

-Robin