Do you consider it a logical impossibility for a human being to know his own future?

If that future is inherently uncertain from within his temporal perspective, then it is logically impossible for the human being to know it, unless of course, a being outside his temporal perspective, were to inform him.

And you believe in Biblical prophecies?

Yes.  But there are a variety of ways in which Biblical prophecies can be reconciled here. 1) If God is confined within our temporal perspective, prophecies could just be events He has determined in advance He will cause to occur.  2) If God is outside of our temporal perspective, then He sees those events as completed facts, and he could of course relay that information to a human in our past as prophecy.

Clearly, most Christians believe it possible, since they believe that God has perfect knowledge of what God himself will do. If God does not, then we fall back into the conundrum that he cannot know ours, since he cannot know whether he will alter ours at some point in his future. Where is the contradiction in God's knowing his own future or anyone's knowing their own future?

Inherent uncertainty is logically inconsistent with knowledge.  If God's future is inherently uncertain from His perspective, then He cannot know it.  And since there is nothing outside of God, there is nothing outside of His perspective, which means God's future, if inherently uncertain from His perspective, is inherently uncertain from any perspective.

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It is logically possible that God can lift any weight against a gravity field, but it is not logically possible that he, as an omnipotent being, can encounter a weight that he cannot lift against some gravity field.

I find it interesting that you included "gravity field" in your hypo. Most people do not. Here you recognize that we have to know what we mean when we talk about "weight." But you fail to apply that lesson to omniscience and to the future.

I think that we know a lot more about gravity than omniscience, which is an imagined trait of an idealized being. We do that by examining how people use the word. They certainly do use it to include precise knowledge of future events.

There is a whole post of mine that you haven't answered which deals in part with this topic, explaining why your notion of omniscience is flawed. Until you answer it, I see no need for a further response on my part.  
 

To assess whether the "future" can logically be known, we must take into account what we mean by the "future." And here we are talking not just about any "future" but "God's future." That in turn requires looking at the nature of time itself. Two questions present themselves. (1) Is the "future" inherently uncertain from within the temporal perspective? (2) Is there a vantage point from outside the temporal perspective from which the "future" can be perceived? If the answer to the first question is "yes" and the answer to the second question is "no", then the "future" in question cannot logically be known.

Your vagueness is unhelpful here, because the answer may differ, depending on whose perspective you are taking. Whereas a human being must answer "yes" to the first question and "no" to the second, and omniscient being must answer "no" to the first and "yes" to the second.

My post is not vague in any respect.  You are the one who wants to have his cake and eat it too.  You assume humanity's future when you say an omniscient being must answer the first question "no" and the second question yes, but then you try to posit a contradiction by switching to God's future.  With regard to the first question, if God's future is inherently uncertain from within God's temporal perspective, then it is not logically possible for Him to know it.  As, I argued right after this passage, you use this to set up your contradiction, saying, if we're talking about God's future, the answer must be "yes" and therefore He is not omniscient.  The problem with that is that the answer to question (2), with regard to God's future, is obviously "no."  If God has a temporal perspective, there is no vantage point outside of that perspective.  That should be painfully obvious, even to an atheist, which suggests to me, that you are simply not paying attention.    

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You exploit (1) in an attempt to show your alleged contradiction between omniscience and omnipotence, but you fail to take into account (2). That is, you posit God has a temporal perspective of His own and you posit that His future is inherently uncertain from within that temporal perspective (because He can change it through His free-willed choices and because He has to react to changes in the "film" due to the free-willed choices of humans). What you fail to take into account is that nothing is outside of God. He encompasses all of reality. Therefore, if He has a temporal perspective, there is no vantage point outside that temporal perspective from which God's future can be perceived. Thus, God's future cannot logically be known.

As I have said repeatedly, humans are not omniscient. Your argument seems to be that no temporal being can ever know its own future. That may be, but it is not a logical certainty. Where is the contradiction in the idea of knowing one's future?

It is a logical certainty if the future is inherently uncertain from within the temporal perspective, unless, of course, that information can be derived from outside of that temporal perspective  Since nothing is outside of God's temporal perspective, His future is unknowable.

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The "timeless" and "instant or two" perspectives I have offered also defeat your objection by positing that God has no future to know. If God is timeless, or His temporal framework includes no future, then there is no future to be known.

Neither of your 'perspectives' are coherent, in light of your determination to use language that is incompatible with them. I've pointed out some of the linguistic potholes that you keep running over, but you seem determined to have your temporal cake and eat it, too. Events cannot be "timeless", since their very definition is grounded in time, yet you persist in describing God in terms of temporal processes that he goes through. You somehow think that you solve a problem by merely declaring that the process is "timeless" (an absurdity) or that it is really really quick--an "instant or two". As far as I can tell, this is a hand-waving response to an unresolvable contradiction when you try to attribute both omniscience and omnipotence to the same being.

Again, you have failed to respond to an entire post of mine that deals with these subjects.  You are now just repeating old claims of yours without addressing my responses.