How cold is it outside? The combined effect of the wind and the temperature determines the rate at which your body loses heat. This combined effect is called the "wind chill factor". The chart on this page shows that the wind chill factor increases with the wind speed up to 40 mph. When the temperature is less than 30° Farenheit and the wind velocity is at least 15 mph, there is a greater danger of exposed flesh freezing. This shows that the air temperature depends on the wind velocity to create a freezing condition.