In chapter 23, what did Atticus foresee?

We've reached Chapter 23 of To Kill a Mockingbird, and Tom Robinson has been falsely convicted of the rape and assault of Mayella Ewell. Atticus is going to file an appeal, and he actually goes so far as to tell Scout that the appeal has a good chance of success. We don't know whether Atticus is just saying this to reassure Scout or whether he actually believes it. But Atticus must know deep down inside that there's almost no chance of Tom's conviction being overturned. An African American man convicted of raping a white woman in the South, even if it's on the basis of a trumped-up charge, is virtually guaranteed to pay with his life, either through lynching or the death penalty. At any rate, in response to a question from Scout, Atticus predicts that, if the appeal is unsuccessful, then Tom will be sent to the electric chair as rape in Alabama is a capital offense.