Anytime it gets windy during the winter, you're sure to hear the wind-chill reported. Just as wet clothes hanging outside dry faster on a windy day, evaporation of water from your skin occurs faster when there's wind. And evaporation is a cooling process.

Where things get tricky is putting a number on the cooling. The wind chill values currently used were developed from experiments with plastic cylinders filled with water. That's a far cry from understanding the wind's effect on a human.

Recently, researchers have suggested revising the wind chill chart to better represent how the skin loses heat. With this revision, most wind chill values would increase by 5 to 10 degrees - that is, the current wind chills may be too low.

In any case, very low wind chill values - say -20^oF or lower - DO serve as a warning that the combination of wind and cold is dangerous.