It's a simple enough calculation:
(CA + BO) + E = NR
Where CA = Cold Air, BO = Bending Over, and E = Exertion.
This is guaranteed to result in NR, or Nose Running.
I don't think I need to expand on that, do I?
It's possible that there is another equation, a slightly more complex one, which involves weather which could be described as "sunny with showers", the presence or absence of a coat, and the likelihood of it actually raining.
Obviously there's a serious sub-set in that one, where the availability of a coat reduces the possibility of rain, whereas the location of the coat being half a mile away, tends to increase the possibility.
Or is it just me?