It's a common misconception: a lot of people think that since your nose
runs when you have a cold AND when it's cold out, it means that cold
weather makes you get a cold. However, the reason your nose runs with
cold weather is completely different and it has to do with your body
trying to keep your nose warm.
There's a couple of reasons for
it: First is, your nose has a ton of tiny blood vessels that it uses to
support all the glands you use to smell. When it's cold out, these blood
vessels expand, sending more blood to your nose. This makes your nose
produce more fluids.
The second reason is that, since the air
you are breathing in is colder, your nose needs to work overtime in
order to warm it up. For your nose, working overtime means making more
snot and making it drip out of your nose.