The East Coast simmered through temperatures climbing toward the century mark.
Ten deaths were blamed on stormy weekend weather, most in the Midwest. Wisconsin Gov. Jim Doyle declared an emergency for 29 counties and President Bush late Sunday declared a major disaster in 29 Indiana counties. Iowa Gov. Chet Culver said nearly a third of his state's 99 counties need federal help.
Rivers in several parts of the Midwest swelled with the runoff from heavy weekend rainfall, topped by the 11 inches that fell Saturday in Indiana.
Water was pouring over the top of Wisconsin's Dell Creek Dam on Lake Delton in Sauk County, and had swept away three houses, county emergency management director Jeff Jelinek said. He was not sure whether there were any injuries, but said people had been told to evacuate the area, which is about 50 miles north of Madison.
The devastation near Lake Denton is tremendous, reports CBS News' Linda Eggert. People are calling it surreal; one lady said it was like a "water slide times 1000."
A couple thousand people in Columbia County, about 30 miles north of Madison, were urged to evacuate below the Wyocena and Pardeeville dams, said Pat Beghin, a spokesman for the county's emergency management.
The Wyocena Dam's spillway had washed out, and workers were sandbagging to try to save the dam, Beghin said. The Pardeeville dam was overflowing, creating a risk for the nearly 10,000 people downstream in Portage, he said.
The Upper Spring Dam in Palmyra was failing, state emergency management officials said. But only one house in the rural area was in danger, Palmyra town chairman Stewart Calkins said.
Wisconsin Department of Natural Resources engineers were being sent across the state to survey other dams.
Wisconsin Gov. Jim Doyle had declared states of emergency for 30 counties. At least 130 inmates from the Department of Corrections were helping sandbag in nine areas, according to the state emergency management. The Red Cross had 11 shelters open across the state and was preparing a 12th, officials said.
A new storm system was headed toward the Ohio Valley from the southern Plains on Monday - Oklahoma got up to 6 inches of rain by late morning and utilities reported nearly 5,000 customers blacked out - and the National Weather Service said as much as 3 inches of rain could fall on already waterlogged Indiana late Monday.
The weather service posted a tornado warning for south-central Illinois and a severe thunderstorm warning for Indiana.
Some 200 Indiana National Guard members and 140 Marines and sailors joined local emergency agencies Monday in sandbagging a levee of the White River at Elnora, about 100 miles southwest of Indianapolis. The White River was forecast to crest Tuesday at nearby Newberry at 16 feet above flood stage.
In Columbus, Indiana, CBS News' Jay Hermacinski reports that regional hospital crews are working around the clock to pump more than six feet of water out of the hospital.
Local officials said they wanted to raise nearly a mile of levees as much as 3 feet.
By Monday morning, flooding at eight sites in central and southern Indiana had eclipsed levels set in the deluge of March 1913, which had been considered Indiana's greatest flood in modern times, said Scott Morlock, a hydrologist with the U.S. Geological Survey in Indiana.
Those sites included Newberry, where the White River reached 28.04 feet Monday morning, topping the record of 26.98 feet set in March 1913.
While the Midwest fought to cope with flooding, the East was locked in a sauna. Heat advisories were posted Monday from the Carolinas to Connecticut, with temperatures expected to hit 100 from Georgia to New York, the National Weather Service said. Raleigh-Durham, N.C., hit a record 101 on Sunday.
The heat and dry conditions fueled an Eastern North Carolina wildfire - more than 30,000 thousand acres have burned, reports CBS News correspondent Bianca Solorzano.
Humidity in the New York City area will make it feel between 100 and 105 degrees, notes CBS station WCBS-TV, adding that the high temperatures will likely last until midweek.
"It's just crazy. ... It's really, really hot," said New York City street worker Jessica Pena as she swept a midtown Manhattan street at around 8:15 a.m. The temperature already was in the upper 80s.
In the fifth inning of the Kansas City Royals-Yankees game in New York, fans cheered loudly when a cloud moved in front of the sun, then booed moments later when the sun returned.
"We came to New York and the whole week is hotter than in Florida," Patti Yost, 47, of Spring Hill, Fla., said at Yankee Stadium.
The heat also wore down tourists in Washington. "We're going to get back on the Metro and go to the hotel and get into the pool," Jeanne Ringel of Redondo Beach, Calif., said outside the Smithsonian's Freer Gallery of Art.
New York City opened 300 cooling centers Monday, said Office of Emergency Management spokesman Chris Gilbride. District of Columbia officials declared Monday and Tuesday Code Red days for poor air quality, and schools in parts of New York, Connecticut, New Jersey, Pennsylvania and Maryland closed early as class rooms heated up. Employees at the Ohio Department of Health got the day off because of trouble with the air conditioning in their building.
PJM, the electric power grid for 13 Mid-Atlantic and Midwestern states and the District of Columbia, issued an advisory saying it expected to meet the surging demand for power but urged customers to conserve.
The weekend death toll included six in Michigan, two in Indiana and one each in Iowa and Connecticut.