Wind chill is an apparent temperature index used in the cold season that describes how cold exposed flesh ‘feels’ given the air temperature and wind speed (wind may act to remove heat energy away from the body). A winter day with a strong wind can seem much colder than one with only light winds, even though the air temperature may be exactly the same. Wind chill is frequently used as guidance in extreme cold events to estimate the length of time required for exposed flesh to freeze (e.g. 10 minutes at a temperature of -10°F and a wind speed of 25 mph).