everything you wanted to know about wind chill.
http://www.weather.gov/om/windchill/windchillglossary.shtml
in a nut shell:
1. What is windchill temperature?
A. The windchill temperature is how cold people and animals feel when outside. Windchill is based on the rate of heat loss from exposed skin caused by wind and cold. As the wind increases, it draws heat from the body, driving down skin temperature and eventually the internal body temperature. Therefore, the wind makes it FEEL much colder. If the temperature is 0 degrees Fahrenheit and the wind is blowing at 15 mph, the windchill is -19 degrees Fahrenheit. At this windchill temperature, exposed skin can freeze in 30 minutes.
2. Can windchill impact my car's radiator or exposed water pipe? back
A. The only effect windchill has on inanimate objects, such as car radiators and water pipes, is to shorten the amount of time for the object to cool. The inanimate object will not cool below the actual air temperature. For example, if the temperature outside is -5 degrees Fahrenheit and the windchill temperature is -31 degrees Fahrenheit, then your car's radiator will not drop lower than -5 degrees Fahrenheit
12. Does windchill only apply to people and animals?
Yes. The only effect windchill has on inanimate objects, such as car radiators and water pipes, is to more quickly cool the object to cool to the current air temperature. Object will NOT cool below the actual air temperature. For example, if the temperature outside is -5 degrees Fahrenheit and the windchill temperature is -31 degrees Fahrenheit, then your car's radiator will not drop lower than -5 degrees