The only effects wind chill and the heat index have are that they can increase the speed at which something freezes or gets hot. If you walk outside with your face exposed at -20f, odds are you can stay there for a very long time with no adverse affects. Add a 20mph breeze and your skin will freeze more quickly even though the ambient temp doesn't change. Anybody who owns a convection oven knows that a small fan placed inside of a standard oven greatly reduces the cooking time of anything you put in there without increasing the temperature.