By KSN Chief Meteorologist Dave Freeman

"It's not the heat, it's the humidity that gets you!" I bet you've heard that old saying a million times. But is it true? Is there really a difference between a blistering hot dry day and a sweltering, humid afternoon? Many old weather sayings turn out to be false but this one is right on the money! But the reason has nothing to do with the atmosphere--it has to do with the way our bodies work to stay cool.

Of course, the human body tries very hard to maintain the proper temperature. When we get hot, the body produces sweat--water on the surface of the skin. This water then evaporates, a process that uses heat. So, the effect is that our skin is cooled.

But what if the air already has a good deal of moisture in it? If that is the case, the sweat does not evaporate as well, and we don't cool down as quickly. The body responds by producing more and more sweat.

In contrast, on one of those blistering hot, dry Kansas afternoons, the relative humidity can be very low--20% or even less! This means that the air is VERY efficient at evaporating sweat, and the body has a comparatively easy time cooling.

One way to measure these effects is with the Heat Index. This scale helps us to track how increasing humidity makes it harder for the body to cool. It factors in the effect that moisture has on the body and gives us a "feels like" temperature. For example, a temperature of 90F with a relative humidity of 40%, "feels like" 91. But increase the relative humidity to 70% and the "feels like" temperature is 105! On the other end, when the air is very dry, the "feels like" temperature can actually be lower than the air temperature!

It is important to keep in mind the dangers of extreme heat and humidity because there are some potentially serious health effects. Heat exhaustion or even heat stroke can result! So remember to drink plenty of the right kinds of fluids, avoid strenuous activity in the peak heat of the day, and enjoy the summer!

Dave Freeman
KSN Chief Meteorologist
weatherlab@ksn.com