Don't Let the Heat Beat You This Summer

Learn How to Read the Heat Index

Find the Relative Humidity Percentage in Chicago

There’s a saying in Chicago that “if you don’t like the weather, wait five minutes, it’ll change.”

Well, the weather has changed in the course of a few days from a cool and cloudy late spring to a sunny, warm and humid early summer and with it the conditions that runners face when they step out the door to start their daily run.

Summer, like winter, presents its own climatological challenges to runners with the foremost, and most potentially dangerous of them, being the combination of temperature and relative humidity.

The human body normally cools itself by perspiration, or sweating. Heat is removed from the body by evaporation of sweat. A high relative humidity reduces the evaporation rate, resulting in a lower rate of heat removal from the body and bringing about the sensation of being overheated.

The calculation of this combination of temperature and humidity is called the heat index (it is also sometimes referred to as a ‘real feel’ temperature.) For example, let’s say the temperature is 86 degrees and the relative humidity is 60%, that will result in a heat index of 91 degrees or what is considered an ‘extreme caution’ zone. But if the temperature remains at 86 degrees, and the relative humidity increases to 90%, the heat index rises to 105 degrees or what is considered to be in the ‘danger’ zone.

If the body cannot properly cool itself a person may experience muscle cramping from the heat, heat exhaustion, or in the more extreme form, heat stroke.

Below is the heat index chart. With a quick search on your preferred weather app or website, you can find the relative humidity percentage. Plug it in the following chart and you can find the current real feel temperature.

heat index 

You can also let this Heat Index Calculator do the work for you. 

Heat Index Calculator


There are several precautions runners can take to limit their risks from the summer heat and humidity. Stop by one of our stores to ask an employee about preventative clothing and accessories that we carry. Here are some quick tips:

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