DALLAS — In the simplest of terms, the heat index is what the the temperature feels like to the body, and it's a pretty long equation to figure out.
On Monday, June 19, North Texas saw a heat index of 116 degrees, and the National Weather Service (NWS) estimates the index peaking on Tuesday to 114 degrees.
NWS offered up this equation to help us calculate the climate phenomenon that has everyone talking:
HI = -42.379 + 2.04901523*T + 10.14333127*RH - .22475541*T*RH - .00683783*T*T - .05481717*RH*RH + .00122874*T*T*RH + .00085282*T*RH*RH - .00000199*T*T*RH*RH
Juan Hernandez is a meteorologist with NWS and says the index is basically what you get when you combine air temperature with humidity. The humidity North Texans are experiencing is about 13 to 15 more degrees than it is outside.
"It's a complicated equation. It has to do with relative humidity, how hot is it, dew point, all that comes into factor here," Hernandez said. "We haven't seen it like this since 1980. In fact, June and July of 1980 was the last time we had heat index values of 116."
Dr. Craig Crandall of UT Southwestern specializes in thermal physiology. He says it's better to just stay inside in the air conditioning. He warns of heat cramps, heat exhaustion, even stroke, which can lead to death.
It all comes down to core body temperatures increasing.
"The more water in the air and that is higher humidity, the less effective that sweat evaporates. And you need to have that sweat evaporate to cool you down," said Crandall.
Sweating is our body's way of cooling down but if the sweat doesn't evaporate because of the humidity, our body temperature continues to rise.
Crandall adds that headaches are very common on high heat index days. He says headaches are some of the first signs of dehydration.