Dr. Larry Kalkstein of the University of Delaware is an expert on the health effects of weather and climate. A few years ago, he helped the local National Weather Service develop a better prediction scheme to identify when hot, steamy weather becomes a significant health concern in our area.

Dr. Kalkstein's methods use temperature and humidity data - as you'd expect. But they also factor in cloud cover, wind, how long the heat spell will last, and whether the oppressive weather is occurring early or late in the summer. He's compared these variables with information about heat-related deaths in the Philadelphia metropolitan area. That may sound morbid, but the result is a computer program that helps the Weather Service decide if they should issue an excessive heat watch or warning for an upcoming bout of oppressive weather.

This procedure has been in place since 1995. During that summer, the City of Philadelphia Health Department estimated that about 300 heat-related deaths were averted thanks to this system.