The National Weather Service has issued an excessive heat warning for a large swath of the United States, ranging from Kansas in the middle of the country to Massachusetts on the northeastern coast.
Forecasters say temperatures will be about 38 degrees in cities such as Chicago, New York, and Boston, and expect them to break records in some instances. The "heat index," the combined effects of heat and humidity, is predicted to reach up to 46 degrees in parts of the East Coast.
The National Weather Service defines an "excessive heat warning" as a prolonged period of high temperatures and extreme humidity that creates life-threatening conditions. Such a heat wave is blamed for the deaths of about 130 people in the western state of California last week.
Local governments are putting safety measures into place such as opening "cooling centers," where residents can step into an air conditioned area for a few hours.
The city government of Boston made automated phone calls to elderly residents on Monday, alerting them to the heat advisory. It will also be making similar automated phone calls to the general public, asking them to check on elderly neighbors.
City governments in the advisory area are taking precautions to protect their electric supplies, especially after problems with the power grid left thousands of New Yorkers without electricity for almost a week earlier this month.
New York has turned off the lights on the city's East River bridges to conserve energy. The federal government has asked its employees in Washington to turn off unattended copy machines and computers to help prevent electricity "brown outs" during the afternoons, when temperatures are at their highest and air conditioners drain power supplies.