Knowing the probability does not make the event itself predictable. By definition, being random, it is not predictable. And if you're using a good source of randomness, like radioactive decay, atmospheric noise, or thermal noise, it is provably impossible to "foretell in advance" what will occur.
You might as well say that drawing a royal flush is a perfectly predictable event, simply because we can define exactly the chance of drawing one (1 in 649,740, to be precise, assuming you aren't picky about suit.) That's not "predictable" in any sense of the word as I would use it. Again, for actually good sources of randomness (most of which are quantum-mechanical in nature), it's literally the opposite of "predictable," in fact--it cannot be foretold in advance, not even in principle.