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High temperatures and humidity were expected to bake a large swath of the United States again on Sunday and send afternoon heat indexes in dozens of cities to dangerous levels, where forecasters predicted they would remain through much of the coming week.
The National Weather Service posted excessive heat warnings for much of the nation's midsection, including Illinois, Wisconsin, Minnesota, Iowa, Missouri, Kansas, Nebraska, Oklahoma, as well as South and North Dakota, where forecasters predicted heat indexes could hit 115 degrees Fahrenheit.
"This will likely be the most significant heat wave the region has experienced in at least the last five years," the weather service said.
The heat wave is expected to press east by the middle of the week, the weather service said.
In Chicago, where the high heat and humidity warnings were twinned with a poor air quality alert, forecasters expected temperatures to hit 95 degrees Fahrenheit in the afternoon, creating heat indexes as high as 105.
