Green’s Dictionary of Slang

(US) to predict.

1904		Ade ‘The Fable of the Society-Trimmers’ in True Bills 80: He was idly snowballing the Lay-Out while waiting for a Friend to get through with a Game of Stud.
1913–14		Van Loan ‘For the Pictures’ in Taking the Count 318: If I knew the answer to that question I’d win myself rich, snow-balling the right round in the mutuals.