In his book Pascal’s Fire, Keith Ward writes:
…ultimate mind is the actual basis of all possible states. It is the only being that must be actual, if anything at all is possible. It is thus uniquely self-existent, not deriving its existence from any other being. Its nature is necessarily what it is–there are no possible alternatives to it, since it is the basis of every possibility. It can be spoken of as omniscient, in the sense that it conceives or generates all possible states, knows what they are and knows that there are no more than it conceives. It can be spoken of as omnipotent, in the sense that it brings whatever is actual into existence from the realm of possibility, or it generates actual beings with a derivative power to make some possible states actual. Nothing that comes into being can have more power than ultimate mind has, since the latter is the source of all actuality.
It might well be as well to note that these definitions of omniscience and omnipotence are not exactly the same as the ones classical philosophers have often given. Many philosophers define omniscience as knowledge of absolutely everything, possible, actual, past, present and future. They define omnipotence as the power to do absolutely anything that is not self-contradictory. The definitions I have given are more restricted than that. They do not entail that God knows what will be actual in the future. Perhaps God leaves the future open for radical freedom. And they do not entail that God can do absolutely anything. Perhaps God leaves, or even must leave, finite reality to follow its own inherent laws of development.
Yet we can still say that God knows everything that is possible and actual (the future may not be actual yet) and that God is the most powerful being there could possibly be and the ultimate source of all things that come into being. This leaves open the question of exactly which possible states can be made actual adn whether there are restrictions on what possible states can be actual. Though such an ultimate mind can sensibly be called omniscient and omnipotent, this may not be enough to satisfy some religious believers. It is enough, however, to satisfy the requirements of being an ultimate explanation of the universe. (pp. 132-3)
Elsewhere Ward speaks of God’s “temporality,” as the divine experience of a succession of states. God is still trans-temporal in the sense of transcending the multiple processes of temporal succession posited by relativity theory. But Ward argues, contra the classical view, that it is a perfection, not an imperfection, for God to experience the flow of new experiences and new possibilities for creativity, in response to real relationships with creatures.
God can enter into many different times, acting and responding in them, while also existing in a trans-temporal way. We cannot imagine this trans-temporality of God, but it should not be conceived as a totally immutable and static existence. It might be better conceived as a transcendent agency that acts incessantly in many temporal streams, manifesting its changeless perfection in continual creative activity, sensitive awareness, and overflowing goodness. (p. 216)
Obviously a lot of argument would be required to establish this position with any confidence, but I think there are two root insights that motivate it. The first is that, if God does not experience temporality in some sense, then God’s knowledge is, paradoxically, limited. That is, there’s a mode of experience that God has no knowledge of. The second is that God, according to the Bible and much religious experience, exists in responsive relationship with God’s creatures. For this to be a genuine relationship and not an illusory one, God must be able to actually enter into the flow of time and, potentially, be affected by it. Classical Christian thought limited this to the Incarnation, but Ward goes further than that here.
So, if there is a temporal aspect to God’s existence, then we can begin to see why omniscience might still allow that God doesn’t know certain things. If there are genuinely undetermined events (and there may be quite few for all we know), then even God would only have probably knowledge of how they are going to turn out. As Ward says, God knows all possible states and all actual states, but non-actual future states would not necessarily be part of God’s knowledge.
I always feel a bit impious even speculating about this stuff.