Midwest and Mid-Atlantic Heatwave Alert: Record-Breaking Temperatures and Extreme Humidity Expected

 NWS HeatRisk Map for Tuesday, August 27th, 2024

Hot Weather Alert: Midwest and Mid-Atlantic Heatwave Expected to Break Records

NOAA/NWS/OpenStreetMap (CC BY-SA 2.0)

A severe heatwave is sweeping across the Midwest, bringing with it extreme humidity levels typically seen in the U.S. Southeast. As this heatwave moves into the mid-Atlantic states this week, the region could experience some of the summer's hottest temperatures, potentially breaking records.

Temperatures are soaring into the mid-to-upper 90s Fahrenheit (upper 30s Celsius), reaching 10 to 15 degrees F (5.6 to 8.4 degrees C) above normal. This heat is driven by a powerful high-pressure system that has migrated from the Southwest, creating a "ridge" that blocks cooler storms and allows for clear skies, intensifying the sun's impact on the ground.

Andrew Taylor, a meteorologist at the National Weather Service (NWS) in Lincoln, Ill., notes, “This is a strong ridge even for midsummer, making it especially unusual for late August. The intensity could lead to record-breaking daily temperatures.”

In addition to the heat, humidity levels are spiking due to moisture from the Gulf of Mexico and "corn sweat"—a process where crops like corn and soybeans release moisture as temperatures rise. This process, known as evapotranspiration, is similar to human perspiration and contributes to higher humidity levels.

Dew points, a measure of atmospheric moisture, are reaching into the 60s and 70s F (upper teens to mid-20s C), with some areas experiencing dew points in the low 80s F (mid- to high 20s C). Dew points above 55 degrees F (13 degrees C) can feel uncomfortable, with anything above 70 degrees F (21 degrees C) becoming oppressive.

With both high temperatures and humidity, the risk of heat-related illnesses increases significantly. Elevated humidity makes it difficult for the body to cool itself through sweating, raising the potential for heat exhaustion or heat stroke. Heat indices, which measure how hot it feels with the humidity, could reach 105 to 115 degrees F (41 to 46 degrees C) in the worst-affected areas of the Midwest.

The NWS's experimental HeatRisk tool, which considers temperature, humidity, and heat-related hospitalization data, places much of the region in the "extreme" and "major" risk categories—the highest levels.

Meteorologists, including Taylor, emphasize the importance of caution during outdoor activities, especially for those who are working, exercising, or exerting themselves. Prolonged exposure to these conditions can result in heat exhaustion or heat stroke, a life-threatening situation.

For those who must be outside, Taylor advises frequent breaks in shaded or air-conditioned areas and to stay hydrated. “Try to limit outdoor activities during late morning to early evening hours,” he adds.

In northern Midwest regions like Minnesota, where the current heatwave coincides with the state fair, college move-in days, and other outdoor events, heat-related health concerns are particularly high. Vulnerable groups, including young children, older adults, people with health conditions, outdoor workers, and the unhoused, are at the greatest risk.

Taylor also cautions against leaving children or pets in vehicles during this heatwave, as there have already been 27 reported deaths of children left in hot cars this year, according to the NWS.

Overnight temperatures will remain elevated, with lows only dropping into the 70s F, adding to the heat stress. Ashton Robinson Cook, a meteorologist at the NWS’s Weather Prediction Center, warns, “When there’s little relief overnight, heat stress increases.”

While heatwaves like this are not unprecedented, they are becoming more frequent and intense due to the added heat trapped by greenhouse gases from burning fossil fuels.

Fortunately, relief is on the way as a slow-moving cold front will begin to push into the northern U.S. late Monday night and early Tuesday, gradually cooling the region.