Hotter Than It Looks

The Heat Index reveals why triple-digit days in Oklahoma can feel even more intense – and what to do about it.

May 26, 2026

thermometer shows a high temperature during heat wave

While Oklahomans cope with the warmth – and oftentimes nastiness – of late spring weather, the clock has already pushed ahead to the inevitable onset of summer and its accompanying searing heat.

In Oklahoma, that heat, which can skyrocket to 100 degrees or higher, is exacerbated much of the time by an unwelcome accomplice: humidity. Higher levels of humidity can make the actual temperature feel hotter than it is. When that happens, the real, in-the-shade temperature reading doesn’t matter all that much.

Meteorologists at the National Weather Service (NWS) have devised a way to measure just how hot it feels outdoors: the Heat Index.

Rick Smith, warning coordination meteorologist for the NWS’s forecast office in Norman, explains that the Heat Index is a way to measure the relative comfort level for folks who want or need to spend time outdoors. when it’s hot. He also passed on some common-sense safety tips for making the best of a sticky situation.

The Heat Index, Smith says, is derived from a mathematical formula. The result “is a way to measure how hot it feels to the human body. The higher the humidity, the hotter it feels during the summer.”

Smith pointed out that official temperatures are taken in the shade.

“So the Heat Index doesn’t take into account that you might be in the sun and not in the shade,” he says. “If you’re in the sun, you’re going to feel much hotter.”

The NWS website explains in detail how the Heat Index is determined, and charts the “feels like” temperature for each degree of relative humidity at any given temperature. When the relative humidity is high, there is lower evaporation from the body; less heat is removed from the body, and the more uncomfortable you feel. Conversely, when the relative humidity is lower, evaporation is higher and more heat is removed from the body and the more comfortable you feel. Smith says the Heat Index formula is a lengthy, complex calculation, and its formula is available on the NWS website.

The standard advice for dealing with intense heat, Smith says, is just to be aware of the weather. People who need to be doing something outside should do it in the morning or evening, rather than in the middle of the day, he adds.

“If you have to be outside, take frequent breaks,” he says, and take advantage of any available air conditioning. “Drink plenty of water – the basic things we talk about for the middle of summer.”

The NWS points out that heat is the leading weather-related killer in the U.S., resulting in hundreds of fatalities each year. Heat can be taxing and can lead to illness, or make existing health conditions worse for older adults, young children and infants, and people with chronic medical conditions.

The good news for Oklahomans, Smith says, is that the state isn’t situated near the Texas coast or anyplace else that deals constantly with intense humidity, along with the expected summer heat. He says long-range predictions for Oklahoma’s upcoming summer of 2026 show an average or slightly above average temperatures.

In reality, he says, there is one given: “It’s gonna be hot.”