Cold weather does NOT cause colds!

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.

(Source)