A massive heat dome is driving extreme temperatures across the central and eastern United States, affecting more than 90 million people. The National Weather Service issued heat alerts in areas stretching from the Gulf Coast through the Midwest and into the Northeast.
Cities like Chicago, St. Louis and Memphis could reach their hottest temperatures of the year, with heat index values — the “feels like” temperature — ranging from 105 to 115 degrees in some areas.
What is causing the high humidity?
Humidity is especially severe in the Corn Belt due to a phenomenon known as “corn sweat.” As corn reaches peak growth, it releases moisture through its leaves, increasing air humidity through evapotranspiration. This added moisture, combined with heat pulled inland by the dome from the Atlantic Ocean, is worsening heat-related risks in states like Missouri, Iowa and Illinois.
According to Iowa State climatologist Justin Glisan, the resulting air can feel as oppressive as a steam room if there is no wind.
How long will the heat last?
The heat will continue to build through midweek, hitting the Midwest hardest on Wednesday and Thursday, before expanding into the Northeast and Mid-Atlantic on Friday. Cities including Detroit, Cincinnati and Philadelphia are forecast to reach the upper 90s or potentially 100 degrees, according to CNN.
Overnight lows will remain unusually high — mid-70s to low 80s — offering little relief and threatening to break records across southern and central states.
What role does climate change play?
Climate Central estimates that human-driven climate change has made this type of July heat at least three times more likely for nearly half of the U.S. population. Their Climate Shift Index shows even higher odds in specific areas like Salt Lake City and Tallahassee.
Experts note that overnight temperatures are rising faster than daytime highs, increasing heat stress and the risk of heat-related illnesses.
Are there agricultural or health concerns?
Extended high humidity can impact crops by elevating plant respiration and lowering yield potential, according to Iowa State University agronomist Megahan Anderson. Those conditions may also support the spread of crop disease.
Health officials continue to stress that heat is the deadliest form of extreme weather in the U.S., with those lacking access to air conditioning facing the highest risk.
