Understanding wind chill

During the winter, a breeze can make a cold day feel more uncomfortable. That’s because wind drives heat away from exposed skin faster than calm air. High winds combined with very low temperatures create dangerously cold conditions. To help people understand the risk, NOAA’s National Weather Service provides wind chill temperatures in reports of current conditions and in forecasts.

“When wind chill temperatures get into extreme ranges, exposed flesh can freeze quickly. If folks venture outdoors in these wind chill temperatures, and they are not properly bundled up, they may risk frostbite or even death,” explains Dave Kellenbenz, a meteorologist in the National Weather Service’s Grand Forks, N.D., forecast office. While dangerous wind chills occur regularly in the northern plains, they can also affect almost any region in the United States.

As temperatures drop below freezing, exposed skin is at risk of frostbite and you become more susceptible to hypothermia. The lower the wind chill temperature, the faster frostbite or hypothermia can occur. Frostbite is the freezing of skin and underlying tissues and can cause permanent damage leading to gangrene and amputation. Hypothermia is a very dangerous medical condition in which body temperature drops and death can follow.

NOAA's National Weather Service wind chill chart and calculator shows the increasing dangers as temperature drops and wind speed increases. In cold winter months, National Weather Service weather forecast offices routinely issue two types of alerts to warn people about dangerously low wind chill temperatures.

• A Wind Chill Advisory is issued when wind chill temperatures are potentially hazardous.

• A Wind Chill Warning is issued when wind chill temperatures are life threatening.

However, temperature criteria for an advisory or warning can vary from state to state to reflect regional climate differences. For example, weather forecasters in Grand Forks, N.D., issue a wind chill advisory when the wind chill is -25° F or lower for more than one hour, while a wind chill of +35° F for at least three hours will trigger a wind chill advisory in Miami.

"People need to stay inside as much as possible when we issue a wind chill warning,” Kellenbenz says. If you must go out, it is best to dress in several layers of loose-fitting clothing to create layers of insulating warm air. A water repellent, hooded outer garment can add extra protection, and a hat will prevent loss of body heat. Mittens are better than gloves at keeping hands warm.

NOAA's National Weather Service began providing wind chill tables in the 1970s. Those early values were based on a wind chill formula developed by Paul Siple and Charles Passel who explored the Antarctic from 1939 to 1941 with Admiral Richard Byrd. Wind chill formulas have since been refined with advances in science, technology, and computer modeling.