You know it's cold when...
the battery in your outdoor thermometer freezes
icicles form on your scarf after just 15 minutes outside
a high of 5 degrees Fahrenheit sounds warm
there is a duck in your kitchen (again)
it takes you a half hour to put on/take off the layers you wear when you go outside
chicken eggs chip the cement when you throw them against it - but the egg doesn't break
water droplets tossed from a mug bounce when they hit the ground
breathing through your mouth makes you cough and through your nose freezes your nostrils shut
your cat won't move from her box near the radiator
a 5 mile per hour breeze feels like gale-forced winds
the soles of your boots don't bend with your feet like you're used to them doing
you have to turn your whole body to look for something that is a bit to your right, just so you can see it (consider the scarf, hood, etc...)
even the sun dogs are trying to get inside
you can almost see the needle on the home's propane tank go down (but that might be the icicle growing on your eyelashes)
you can actually feel the difference between -30 degrees F and -20 degrees F
what you thought was the sound of a bird chattering away was just its knees knocking together
baling wire breaks when you try to bend it
you feel better only after you remind yourself of the winter you spent in Duluth where the temps didn't get above zero for the whole month of January...