Here's one of those story problems you hated in math class.
Let's say that there is a massive heat wave in southern Wisconsin this weekend, and the ambient temperature on Saturday get's up to 10 deg F. Given the balmy conditions, a hypothetical cyclist named Tom decides that he will take a relaxing ride on a north-south rail trial. Before the ride, Tom watches the weather on the tele and discovers that the prevailing wind is out of the north at 10 mph. Tom begins his ride to the north, directly into the wind and averages 10 mph on the bike.
During the initial part of Tom's ride, is the wind chill Tom experiences determined by the 10 mph wind (10 mph, -4 deg F), or is it determined by the 10 mph wind plus Tom's average speed of 10 mph (20 mph, -9 deg F)?
What is the effective wind chill on Tom's return trip if he averages 10 mph?