Chicago (CNN) -- Temperatures dipped in many states Sunday, offering relief from a deadly heat wave which is blamed for 150 deaths across the country since July 19.

In Illinois, where 50 people died as temperatures soared above 100 degrees Fahrenheit, authorities said an additional 20 deaths may be heat-related. Chicago Mayor Richard Daly urged residents to check on relatives and friends, particularly those
who were elderly or ill.

"You could save their life," he said. In 1995, more than 700 elderly Chicagoans died in scorching heat. Daley warned that more deaths could be discovered over the next few days.

Thousands in the Windy City were forced to endure the heat without air conditioning or fans because of sporadic power outages and brownouts.

As the temperature peaked at 104 Friday at Chicago's Midway Airport, up to 100,000 homes lost power. Utilities blamed excessive demand for the outage.

"Several high-rise buildings with elderly were (partially) evacuated." Some cooling centers were down, phone lines were swamped with calls from people who couldn't get through to Commonwealth Edison and wanted to report the outages, city spokesman Terry Levin said.