Welcome to the Forum, fimbriae!
I'm not absolutely sure of the infallibility of the usage being cited, but my online Merriam-Webster's 11th Collegiate Dictionary lists the verb "snowball" as follows:
snowball
Function: verb
Date:1843
intransitive verb
1 : to engage in throwing snowballs
2 : to increase, accumulate, expand, or multiply at a rapidly accelerating rate
transitive verb
1 : to throw snowballs at
2 : to cause to increase or multiply at a rapidly accelerating rate
I would suppose that the usage you mean for it is that of intransitive-2 or transitive-2.
