I have that problem even when it's not that cold! I think between the increased cardio effort and the fact that i'm leaning forward onto my handlebars, all the snot tends to rush to the exit.

I have no problem with snot rockets, as long as they're not landing on me! (I haven't yet learned to aim with it, though, and actually I use it when i run, ski, climb too! The all-purpose skill!)

K.