Heartworm prevention schedules

I know seasonal heartworm prevention relies upon typical weather, since heartworms can only survive in weather that is consistently above 55 degrees for some period of time (correct me if I am misrepresenting this). The schedule for my area is June-November. But since we've had a pretty mild winter, should I be amending this schedule in any way for the best protection? Any information or opinions on this are greatly appreciated.