You know it is cold when:

You walk outside and say, "Oh, it isn't that bad out today." It is -8 Celsius.

When you walk outside, your breath catches in your throat (causing a hypoxic episode), your eyelashes freeze, followed by your nose hairs.

You wash your windshield at the gas station, but it freezes before you get a chance to wipe it off and you are left scraping the windshield muttering under your breath. (true story)

Your fridge dwindles to mayonnaise, a block of cheese and a bottle of soy sauce before you force yourself into the cold to the grocery store.

You see smoke down the road. When you get closer, you realize it is just a group of people breathing.