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 (-1 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.