Americans dipped into the water, went to the movies and rode the subway just to be in air conditioning Saturday for relief from unrelenting heat that has killed 30 people across half the country.

The heat sent temperatures soaring over 100 degrees in several cities, including a record 105 in Washington, St. Louis (106), and Indianapolis (104), buckled highways and derailed a Washington-area train even as another round of summer storms threatened.

If people ventured outside to do anything, they did it early. But even then, the heat was stifling.

"It was baking on the 18th green," said golfer Zeb Rogerson, who teed off at 6 a.m. at an Alexandria, Va., golf course but was sweltering by the end of his round.

The heat sent temperatures soaring in more than 20 states to 105 in Louisville, Ky., 101 in Philadelphia, and 95 in New York; besides Washington, a record of 104 was set in Sioux Falls, S.D., and Baltimore set a record at 102.

At least 30 deaths were blamed on the heat, including nine in Maryland and 10 in Chicago, mostly among the elderly. Three elderly people found dead in their houses in Ohio had heart disease, but died of high temperatures in homes lacking power because of recent outages, officials said. Heat was also cited as a factor in three deaths in Wisconsin, two in Tennessee and three in Pennsylvania.

Officials said the heat caused highways to buckle in Illinois and Wisconsin. In Maryland, investigators said heat likely caused rails to kink and led a green line Metro train to partially derail in Prince George's County on Friday afternoon. No one was injured, and 55 passengers were safely evacuated.

Thousands of mid-Atlantic residents remained without power more than a week after deadly summer storms and extreme heat struck the area, including 120,000 in West Virginia and some 8,000 in the suburbs around Baltimore and Washington, D.C. In the Washington area, Pepco asked customers to conserve power, saying the heat was stressing the system.

"This is becoming a black swan of heat waves, in the sense that it's such a long heat wave, such a severe heat wave and encompassing such a large area," said Chris Vaccaro, spokesman for the National Oceanic and Atmospheric Administration.