While Gordon Clark devotees may wax long and eloquent on this subject, the true answer starts with understanding what God has revealed about himself. God is both in and outside of space and time. "In the beginning, God" was not just a statement of chronology, it is also a statement of his eternality in all three persons of the godhead. God is inside time and space through his dealings with mankind. Jesus occupied a physical place in linear history during his incarnation. God holds the universe together by the word of his power. He sets up and removes kings. All these things the scripture tells us about how God acts in human and cosmic events. God is outside of time and space because he is the creator of all things, including the law of physics. He existed before the physical laws he created to govern his creation.
If you dwell upon this aspect of God, it is difficult to imagine that anything can take place in human events that escapes the knowledge of God. More than that, how can a God, who created all things and the laws to govern all things, not also direct all things? How can God keep himself from knowing? The very idea is antithetical to the nature of God. We are guilty of looking at the complexities of human choices/possibilities and trying to reduce them to an algorithm in order to provide a degree of certainty to our ever inquisitive minds.
If scripture even alludes to God advocating a probability it is more for our sake then his. When Moses spoke on behalf of God, "choose life" (Deu. 30:19), was he waiting in anticipation as to who would choose him? If God is truly omniscient then the answer can only be, "no." But is the idea of probability alive and well within men? Certainly. As finite creatures we cannot help but exist in the world of uncertainty, probability and possibility. What we must careful of is not to transfer our finite reasoning to God. We may explain him in such ways, but we cannot go beyond that line.
I've used an object lesson in teaching ontology and omniscience from God's perspective. Draw a large circle on a piece of paper. Next, draw a horizontal line in the middle of the circle stopping just short of connecting the line to either side of the circle. Basically you are creating a north and south hemisphere without connecting the dividing line to the actual circle. The circle represents God. The horizontal line in the middle represents linear time. The far left of the line is the creation event. The far right of the line is the end of the age. Every human and cosmic event occupies a spot on the linear line. The creation of Adam, the birth of Christ, the Civil War, Neil Armstrong's first step on the moon, and ultimately the ushering in of the eternal state. You and I occupy a spot on that linear line. Mere specks we are. God, as the circle, surrounds all of linear time. He sees pre-creation eternity, linear time, and post-creation eternity as happened, happening, and yet to happen. Where the object lesson breaks down (and actually makes it an even stronger illustration) is that the circle has borders. God has no borders. Borders are constructs of the human mind, allowing us perspective. God is beyond even that. Our minds lack the ability to comprehend the magnitude of this truth, and yet here we are discussing whether God knows all possibilities and probabilities.
