Indiana will witness its first real heat wave of 2016 this week. Temperatures are expected to peak in the mid-90s this weekend, and the National Weather Service has issued a heat advisory through Saturday evening.
The hot conditions are the result of a so-called “heat dome,” which is exactly what it sounds like. Even though the name is simple, the conditions that create a heat dome are a complicated combination of pressure, temperature and air density.
Purdue Earth, Atmospheric and Planetary Sciences Professor Mike Baldwin says it’s helpful to think of the heat dome as a big column of air many states wide. He says less-dense warm air creates a taller column than cold air.
“If you slice through at an upper level, and you look at how much air is above you—that’s really what pressure is, it’s the weight of the air above you—and in the warmer column you have more air above you,” he explains.
Baldwin says that higher pressure air in the top of the atmosphere pushes the heat down toward the ground, creating sweltering, unpleasant conditions.
Additionally, the weekend’s conditions may feel even more unbearable, thanks to a phenomenon some have dubbed “corn sweat.”
“Corn sweat”— or “transpiration” to scientists -- occurs when water inside plants evaporates into the air. Baldwin says corn is better at transpiration than almost any other plant. After the water in corn evaporates, it just keeps pulling more moisture out of the earth.
“The plant is acting like a straw for the air to suck moisture out of the ground,” says Baldwin.
That means heat waves can feel especially muggy in Indiana during July and August, because corn crops are releasing ground moisture into the air.
“If you look at the weather observations, the humidity is going to be higher in the Corn Belt,” he says. “Look around here in Illinois, in Iowa, you’ll see this pool of moisture that’s due to this transpiration process.”
The NWS expects relief early next week in the form of cooler Canadian air.
