CHICAGO, ILLINOIS — Nearly the entire eastern half of the United States will feel dangerous heat and humidity next week, with high confidence that heat index values will exceed 100 degrees across multiple states on several consecutive days. Regional heat index guidance for Wednesday, July 1 shows widespread values of 100 to 106 degrees across Illinois, Indiana, Ohio, and Michigan, with some areas approaching 107 degrees or higher.
The heat dome building overhead is expected to trap low-level moisture under the ridge, sending apparent temperatures to dangerous levels from the Plains through the Great Lakes and into the Mid-Atlantic. Several states are expected to exceed 100 degrees on the heat index for multiple days during the upcoming week.
High Confidence for 100 Degree Heat Index Values Multiple Days
Forecasters express high confidence that heat index values will surpass 100 degrees across the core of the heat dome zone on multiple days next week. Wednesday July 1 guidance shows 100 to 106 degree heat index readings stretching across a wide swath from the central Midwest through the Great Lakes states, with the most extreme values concentrated across Indiana, Ohio, and the lower Michigan Peninsula.
Illinois Indiana and Ohio Face the Most Intense Heat Index Values
The highest heat index readings on the July 1 map are concentrated across Indiana, Ohio, and southern Michigan, where values of 103 to 106 degrees are widespread. Illinois communities will also see heat index values reaching 100 to 104 degrees, making outdoor conditions dangerous for unprotected individuals throughout the afternoon hours.
Great Lakes Region Sees Sharp Contrast Between Land and Water
The regional heat index map shows a sharp contrast between the extremely hot land areas and the cooler air over the Great Lakes themselves, where lake surface temperatures remain much cooler. This contrast will not provide meaningful relief for inland communities, where the heat dome will dominate conditions regardless of proximity to the lakes.
Eastern Half of US Broadly Under Dangerous Heat Next Week
The heat event extends well beyond the Midwest, with dangerous heat index values covering a massive footprint from the Plains eastward through the Mid-Atlantic and into the Southeast. Residents across all affected areas are urged to take heat safety seriously throughout the week.
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