Turns out going outside when it's cold and wet pretty much never makes a difference in the normal course of things. Hypothermia is the exception, and for the most part that means going outside cold, wet, and without much clothing for prolonged periods of time to the extent you're likely chattering the daylights out of your teeth.
This is an important finding since current parenting styles (at least in temperate areas of the US) often include keeping the kids inside much of the winter to prevent them from getting sick. The consequent lack of exercise and being in close quarters with disease vectors (other kids) yields the result of sick, fat kids. I tell my patients to send little Cindy and Juan outside with a good coat when it's cold and wet, unless the little buggers are going to slip on the ice or are shedding genuine tears of misery in a prolonged fashion, which I personally think is good advice for grown up nerds as well, present company included.