Its pretty cold. Its cold enough any wet or dampness on your skin (think inside your nose, wet hair) will freeze pretty quickly. Frostbite can set in very quickly at these temperatures, so you just need to be careful being outside for too long when its that cold.

When I was in high school, I used to do cross country ski racing on the school team. There were many times when it was -15 or so outside, and all we got to wear was some long underwear and nylon speed suits. That was bitter cold. The technology for all that stuff has changed a lot in the last 20 years and its probably not so bad now, but as a kid, it was sometimes so cold it hurt.