August 26, 2024
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‘Corn sweat’ and climate change bring heatwaves to Midwest
Heat wave sends temperatures soaring across the Midwest, And “corn sweat” is causing humidity to spike.
NWS heat risk map for Tuesday, August 27, 2024. NWS heat risk map for Tuesday, August 27, 2024.
The hot weather, combined with extreme humidity typically found in the muggy Southeast, will blanket much of the Midwest and move into the Mid-Atlantic states this week, bringing the hottest weather this summer and potentially leading to further record breaking.
Temperatures will rise into the mid- to upper 90s F (upper 30s C), 10 to 15 degrees F (5.6 to 8.4 degrees C) above normal for this time of year. This is due to high pressure moving into the region from the southwest. Such areas, called ridges because they appear on pressure charts, block cooling storms. Clear skies associated with the high pressure allow sunlight to pour down on the ground, warming it.
That’s “a strong ridge for midsummer,” especially so late in the season, said Andrew Taylor, a meteorologist with the National Weather Service’s (NWS) Chicago office, and its strength could lead to daily temperature records being tied or broken.
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The heat comes with moisture from two sources: moist air flowing in from the Gulf of Mexico and a phenomenon called “corn sweat.” The latter occurs when corn, soybeans and other crops give off moisture as temperatures rise. The process is technically called evapotranspiration, and it’s similar to when humans sweat in the heat. The steam from these crops “is what allows us to see some of the highest humidity levels of the year at this time of year,” Taylor says.
This influx of moisture is pushing dew points (the temperature at which air cools and water vapor begins to condense from the atmosphere) up into the 60s and 70s F (low to mid 20s C). In some places, dew points are reaching the low to mid 80s F (mid to mid 20s C). Below 55 F (13 C), it’s pretty dry and comfortable, but it starts to get muggy around 60 F (16 C), and downright uncomfortable once it hits the 70s.
The risk of heatstroke increases significantly when both temperature and humidity are high. When humidity is high, the air already contains a lot of moisture, making it harder for sweat to evaporate and therefore harder for you to warm yourself through sweating.
The heat index, which measures how hot it feels due to humidity, is expected to reach 105 to 115 degrees Fahrenheit (41 to 46 degrees Celsius) in some of the hardest-hit areas of the Midwest. (The heat index takes into account shade, so places in direct sunlight will feel even hotter.)
Heat risk — an experimental new tool from the NWS that incorporates data on temperature, humidity and when heatstroke hospitalizations tend to increase in certain areas — is in the highest “extreme” and “severe” categories for much of the region.
Taylor and other meteorologists stress that people should be extremely careful when doing anything outdoors, especially when working, exercising, or participating in any other activity that involves strenuous exertion. Prolonged exposure to these conditions can lead to heat exhaustion, with symptoms including fatigue, dizziness, nausea, and cessation of sweating. If a person with these symptoms does not move to a cooler place or receive immediate treatment, heat exhaustion can progress to heat stroke. In the latter, the body loses its ability to cool itself, creating a very dangerous situation.
If you must be outside, Taylor says you should take frequent breaks in the shade, find an air-conditioned spot if possible, “limit your time outdoors to late morning and early evening,” and drink plenty of water.
Heat-related health concerns are especially high in Minnesota and other parts of the upper Midwest because the current heatwaves coincide with the region’s bustling state fairs, college move-in days and other events that “bring a lot of people outdoors,” said Joe Calderone, a meteorologist with the NWS Twin Cities office. Those concerns are especially high for high-risk groups, including young children, older adults, people with various health conditions or taking certain medications, people who work outdoors and the homeless.
“If you have small children, always check the back seat before getting out of the car,” Taylor said. According to the NWS, 27 children have died so far this year after being left in hot cars. Taylor also warned about the dangers to pets if they’re left in cars or outside for long periods of time.
Nighttime temperatures will also rise, with lows only reaching the low 70s Fahrenheit, further increasing the risk of heatstroke. “When temperatures barely drop at night, that creates even more stress for people with heatstroke,” said Ashton Robinson Cook, a meteorologist and forecaster with the NWS Weather Prediction Center.
Heat waves like this one were never unheard of, or even rare, before, but greenhouse gases trapped in the atmosphere from burning fossil fuels are making them hotter and more frequent than ever before.
But the heat wave won’t last long. A slow-moving cold front is moving into the far northern U.S., creeping under the heat wave late Monday night into early Tuesday morning. Then, “ultimately, the bulk of the heat and the most severe heat index will move eastward,” Cook said. Eastern regions will also see some cooling later in the week as the cold front continues to move eastward.
