Most of Iowa is under an excessive heat warning, where temperatures will reach in the 90s and heat index values could be as high as 110 degrees.
The National Weather Service says the heat warning is for the two-thirds of the state south of Highway 20. The warning started 1 p.m. Wednesday and goes until 7 p.m. Saturday.
Paul Fajman, a meteorologist with the National Weather Service in Omaha, which forecasts for southwest Iowa, said Iowa is seeing several consecutive hot days because it’s stuck in a pattern.
“We have an upper level ridge in place over the central part of the country,” Fajman said. “That’s providing southerly flow, which is allowing warmer temperatures to advect northward there. This type of pattern, we don’t have a lot of cloud cover either, so we’re getting a lot of daytime heating with the sun.”
Typically, Iowa sees a heat wave “of some magnitude” every year, said Jeff Zogg, a meteorologist with the National Weather Service in Des Moines.
“And this year is no exception,” Zogg said. “It’s just that this particular one will be the most intense and longest lived that we’ve seen yet this year.”
Too much exposure to high temperatures can cause heat exhaustion and heat stroke. A person with heat exhaustion may sweat a lot and have muscle cramps. Heat stroke is more severe: A person’s high body temperature could trigger an altered mental state and seizures.
When the body is unable to cool itself any further, its core temperature increases. If the brain gets too hot, it tends to shut down, resulting in heat stroke, said Ed Piasecki, a family nurse practitioner with UnityPoint Health in Urbandale.
“Often a person will pass out or become less active in attempts to cool the brain,” Piasecki said. “If that does not happen, the brain will start acting up in ways such as convulsions or shaking or impaired mental function.”
People particularly prone to heat-related illnesses include those who are taking medications for blood pressure or heart failure. Piasecki said some medications keep blood pressure artificially low, but also cause people taking them to lose more water. If the temperature is hot enough outside and the body's cooling mechanism can't keep up, a person is at a higher risk of developing heat exhaustion and heat stroke.
Piasecki said urgent care tends to see a lot of both of these heat-related illnesses.
“Somebody will pass out and they’re concerned they’ve had something wrong with their heart. And they often don’t realize that heat is a powerful precipitator of events such as passing out or fainting,” Piasecki said.
Heat-related illnesses can be prevented by hydrating with lots of water and alternating with another drink like tea or orange juice, and spending time in cooler, shaded areas, he said.
Sunday may be the first day of relief from the heat. The National Weather Service expects temperatures to dip below 90.