Science cannot say that there is no God, no evidence for God, or that God is not knowable because He is by definition beyond the detectability of laboratory experiments, and His existence offers the best inferential answer to explain some observable data.
As far as Richard Dawkins naturalistic assertion “that what is knowable is what is observable,” we may respond to that dictum in the following ways. First, science has a long history of discovering things that existed long before they were observed through the five senses, one example being the atom. Second, science often concludes by inference that some material entities exist, such as genes, electrons, and other planets. Similarly, we know God presently by inference and spiritual experience, but He will one day be observable and knowable to all. Therefore, to believe in His existence today is reasonable, and I believe the best explanation of certain observable phenomena the universe, love, morals, etc.
 See Antony Flew’s book, There Is a God: How the World’s Most Notorious Atheist Changed His Mind, (New York: Harper One, 2007).