Heat dome to amplify summer swelter

· 4 min read

Heat dome to amplify summer swelter

A steamy mélange of high pressure, humidity from the Gulf of Mexico and corn sweat are generating an incredibly uncomfortable summer forecast.

Starting Wednesday, Nebraska will be under a massive high-pressure system that is forecast to send temperatures above the 100-degree mark. Heat index values — known as apparent temperature, which is what the temperature feels like to the human body when relative humidity and air temperature are combined — are projected to be greater than 110 degrees in Lincoln between July 20-22.

The pattern is known as a heat dome, a phenomenon that traps lower pressure air at the surface, reducing cloud cover and allowing the sun to heat the Earth’s surface.

“If it wasn’t the middle of summer, this is a weather pattern that would be rather pleasant,” said Adam Houston, an associate professor of earth and atmospheric sciences at the University of Nebraska-Lincoln. “Unfortunately at this time of year, this pattern gives full opportunity for the sun to cook the ground and get things uncomfortably hot.”

Counter-clockwise atmospheric rotation around the massive high-pressure system will bring south winds, which will draw moisture and heat from the Gulf of Mexico into the Midwest. The hot, moist gulf feed will mingle with Nebraska air that will be heated by clear skies and an influx of moisture being released by plants, primarily corn and soybeans.

Plants, like humans, “sweat,” releasing water through evapotranspiration in an attempt to cool off as temperatures rise. This increased moisture, dubbed “corn sweat,” adds a noticeable amount of water to the air, increasing local humidity levels.

“If it wasn’t for the added moisture from foliage, we would expect, for the most part, the same amount of moisture in the air from Texas to Nebraska,” Houston said. “However, the amount of moisture added by corn, soybeans and other plants is significant to the atmosphere.”

While the increased heat index values will be dangerous to humans, it will also tax developing crops.

“Elevated night temperatures in the upper 70s to low 80s are definitely a major concern with developing crops,” said Al Dutcher, state climatologist and associate geoscientist with the survey division of Nebraska’s School of Natural Resources. “It has the potential to interrupt the normal resting and respiration process of the crops and result in reduced yields.”

Basically, Dutcher said, elevated nighttime temperatures do not allow corn and soybean crops to rest and save energy for the development of kernels and beans. Rather, that energy is used at night to release moisture as the plants continue cooling efforts via evapotranspiration.

“Energy created during photosynthetic time during daylight hours is used to cool plants rather than for the development of corn ears or soybeans,” Dutcher said. “This week is going to be ugly but, luckily, it’s a short term situation that most likely will not have long term effects on grain fill.”

Dutcher said the increased temperatures will also cause stress on farm animals. Information on reducing heat stress on animals is available via Nebraska Extension resources.

Extended forecasts predict that temperatures in the state will drop back into the low 90s by July 24.

The mix of extreme heat and humidity is dangerous because it slows the evaporation of sweat, which is the human body’s primary method of cooling itself. In the short term, individuals can reduce their heat stress through a variety of mitigation measures, including: hydration; wearing heat appropriate clothing; taking adequate rest breaks if working outdoors; and education about the signs of heat stress. For more information on dealing with extreme heat, click here.

The university also issued a message to campus outlining ways faculty, staff and students can help reduce the impact of the heat wave on the university’s energy infrastructure. That message is available here.

While the heat dome will bring extreme temperature conditions, Houston said it will not result in an increase in stormy weather.

“The heat will be oppressive, but it will also suppress all thunderstorm activity,” Houston said. “However, when the pattern starts to erode and allows cold fronts back into the region, then the mechanics for storms will return.

“When that transition happens, I would not be surprised to see some storms form across the region.”

And, Dutcher said the pattern of a few hot, humid days followed by storms will continue through August.

“It’s going to be uncomfortable and we’ll have to deal with it,” Dutcher said. “But, it’s not just going to be a few days this week. It’s summer in Nebraska and this sort of pattern is going to be a problem off and on.”

The sun skirts UNL's Mueller Tower on July 18. A high-pressure system is expected to raise Midwest temperatures to dangerous levels from July 20-22.
Troy Fedderson | University Communications
The sun skirts UNL's Mueller Tower on July 18. A high-pressure system is expected to raise Midwest temperatures to dangerous levels from July 20-22.
Heat index chart
National Weather Service | Courtesy image
Heat index chart
Adam Houston
Al Dutcher

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