You wake up on a frigid winter morning and check the weather on your phone. It says it's 38 degrees Fahrenheit (3 degrees Celsius) outside with a wind chill of 31 degrees Fahrenheit (negative one degree Celsius). So, freezing. But when you look out the window, you can clearly see puddles of liquid water. Not freezing. What's up with that? This is what: wind chill doesn't tell you whether it's freezing outside; it just predicts how fast you'll get frostbite. And, as it turns out, it's even pretty lousy at that.