Chicago ? The blowtorch heat that blistered California last week gripped the Midwest on Monday, prompting communities to throw air-conditioned buildings open to the public and endangering millions of people with outdoor jobs – including NFL players in training camp.

Temperatures throughout the Midwest and Plains rose into the upper 90s and in some places exceeded 100 degrees. The heat index, a measure of temperature plus humidity, climbed as high as 110.

The National Weather Service issued heat warnings for such cities as Chicago, Cincinnati, Dayton, Ohio, and Tulsa, Okla.

The Midwest could get some relief by Wednesday, but the worst of the heat was expected to drift into the Northeast today, bringing scorching temperatures to New York, Washington and Boston.

NFL teams closely monitored players for signs of heat-related illness. The heat prompted the Chicago Bears to cancel morning practice at training camp in Bourbonnais, Ill. On Sunday, the Tennessee Titans let defensive tackle Albert Haynesworth leave practice early after he suffered dizziness.

Chicago resident Tony Tesfay, 43, left his basement room at a halfway house first thing Monday and rode his bicycle to one of the city’s cooling centers – air-conditioned recreation centers and other buildings that were opened to the public to prevent a repeat of 1995, when a heat wave killed 700 people in Chicago.

“I was pedaling slow, not too hard, so I could keep hydrated,” he said. “It took me about 15 minutes. It wasn’t too bad.”

In California, the sweltering heat that punished the state for two weeks subsided, but the number of confirmed or suspected heat-related deaths climbed to 164 as county coroners worked through a backlog of cases.

Cities across the Midwest urged neighbors to check on the elderly and disabled. Utilities expected to set records for power usage and asked customers to conserve electricity to prevent blackouts. About 110 large industrial customers in Wisconsin had their electricity turned off because of the heightened demand. Wisconsin Power and Light Co. said those customers pay a lower rate throughout the year, but the utility can shut off their power when demand increases.

In Oklahoma, authorities reported two more deaths that happened over the weekend. In Missouri, officials announced that a 71-year-old woman had died during the weekend in St. Louis.

In Nebraska, high temperatures, a drought and strong winds combined to feed enormous wildfires near the Panhandle town of Harrison.