system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do i get a runny nose when its cold outside?
gpt
There a couple of reasons for this.  
1) Your body wants to inhale nice, warm air.  Mucous helps to warm it up. 

2) To help you warm up, your body also expands its blood vessels.  This allows more liquid to enter the nasal passage that can then be turned into snot.  

3) As you exhale, it is possible for the vapor in your breath to further add liquid to the mucous in your nose.  

This is as opposed to seeing a runny nose when one is sick.  This is done to "plug up" the nasal passages where the bugs are and prevent it from moving to the lungs.