Heat and humidity can harm the unwary

More than three decades ago in 1979, R.I. Steadman of the National Weather Service developed today’s widely-used heat index, which shows the temperature that the human body actually feels.

The heat index is calculated by combining air temperature, dew-point and relative humidity levels. For example, an air temperature of 85 degrees Fahrenheit combined with a relative humidity reading of 80 percent results in a heat index of 97 degrees. Although the reading is only 85 degrees, the high humidity levels would make it feels like 97 degrees to the human body. A 90-degree temperature combined with a 90 percent relative humidity level would push the heat index up to a very dangerous 122 degrees.

Combined high temperatures and humidity levels, sunstroke, heat exhaustion, muscle cramps and numerous other health problems, including heart attacks, are likely to increase both in number and severity. The age and the health of the individual become extremely important factors in coping with such hazardous weather conditions.

Prolonged exposure to high heat can prove fatal. Since the Dust Bowl days of the 1930s, more than 25,000 Americans have died during various heat waves, mainly in the desert Southwest and regions east of the Rockies, particularly the Deep South and the Southeast.

The heat index readings are normally far lower in the northern and western parts of the country, including the Inland Northwest. That’s because humidity and dew-point levels are often much lower than most areas east of the Continental Divide during the hot summer months.

In our region, the warm, humid air from the Gulf of Mexico is blocked by the Rocky Mountains. Although we do see some triple-digit readings, the relative humidity levels are generally less than 20 percent, hence only a slight rise in the overall heat index.

One should use caution in the outdoors if heat index readings are between 85 and 91 degrees. Use extreme caution with heat index temperatures from 92 to 103 degrees. Conditions become dangerous with indices from 104 to 125 degrees. It becomes “extremely dangerous” or deadly with heat index levels above 125 degrees.

One of the most deadly heat waves in our nation’s history occurred in Chicago July 13-15, 1995.

In the southwestern part of that city on July 14, 1995, the heat index soared to near 130 degrees killing more than 500 people. The day’s high was a record 109 degrees with a relative humidity level of 80 percent.