What year did the wind chill factor and the heat index become part of the weather report?
The heat index was introduced in the early 1980s, replacing the old temperature-humidity index (THI), which had been used for years. It is a single, “apparent temperature”–how hot the air feels at a given temperature and relative humidity. The wind chill index, which quantifies the combined effect of wind and temperature on human flesh, was introduced into public forecasts in the late 1960s and the practice gained prominence and acceptance during the severe winters of the 1970s and ’80s. However, studies showed the reported wind chills were unrealistically low and the formula was revised in 2001. Wind chills that previously computed to the minus 80s and minus 90s now were in the minus 55 to minus 60 range.