Most of December has been seasonably mild. As of Monday, the monthly average temperature sat at 32.8°, which is exactly six degrees above normal. However, the last two days of this month will shave a little off that average with temperatures expected to be well below normal.  Making matters worse is the wind, which makes a cold day feel even more uncomfortable. That's because wind drives heat away from exposed skin faster than calm air. Strong winds along with cold temps create dangerously weather conditions. That's why we talk about wind chill factors on cold days to help people understand the risk they face with prolonged exposure to the cold. Exposed skin is at risk of frostbite.  Frostbite is the freezing of skin and underlying tissues and can cause permanent damage. The lower the wind chill temperature, the faster frostbite or hypothermia can occur. Hypothermia is a very dangerous medical condition in which body temperature drops and death can follow. Take a look at the National Weather Service's wind chill chart and use the calculator to see 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.

When the forecast calls for cold and wind, the best thing you can do to stay warm is dress in several layers of loose-fitting clothing to create layers of insulating warm air. It's also important to wear a hat to prevent loss of body heat. And 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.