The wind chill index is a measure that describes how cold it feels outside when the wind is factored in with the actual air temperature. It combines the effects of wind speed and temperature to indicate the potential for frostbite and hypothermia. The index is particularly important in winter, as strong winds can make cold temperatures feel much colder than they are. The formula for calculating the wind chill index was developed by the National Weather Service and is widely used in weather forecasts. It helps people understand the risks associated with cold weather and encourages them to take precautions when spending time outdoors in chilly, windy conditions.