Scorcher!

The Midwest and Southwest are getting the worst of things, but it's more than hot in over a third of the U.S., including the central Mississippi valley, the Southeast, Texas and parts of California, with temperatures topping 90 degrees and in many cases soaring past 100.

The weather - in some areas combined with drought - has prompted many cities to open cooling centers and take other measures to save lives in what can be killer heat.

So far three deaths in Chicago are suspected as heat-related, and in Arizona, as of Saturday, at least 21 people had died, many of the Arizona victims were homeless, prompting officials to take action.

"Unfortunately for the homeless population that is not used to it, that's where the deaths occurred. That's why Phoenix went out of its way to make sure it focused on those in need," Phoenix Mayor Phil Gordon told CBS News' Early Show co-anchor Hannah Storm.

"We have so much heat across such a large portion of the country - even Las Vegas last week got to 117 degrees - all these temperatures which are above normal in many spots," says CBS News Meteorologist Michael Stroz. "That happens every few years. Some say that records are made to be broken, so we're just breaking them... Some meteorologists will say it's global warming, others will say it's just part of the cycle."

Sunday afternoon, temperatures at Chicago's Midway Airport had reached 104 degrees, just one degree lower than the highest temperature ever recorded in the city.

Other parts of the Midwest also reached triple-digit temperatures. Temperatures hit 102 degrees in St. Louis and 101 in Iowa City, Iowa.

The heat index - the combination of the heat plus the humidity - is even higher and calls for common sense precautions.

"For instance," says Stroz, "it may be 90 degrees, but when you factor in high humidities, it makes it feel hotter than it really is - sticky, real uncomfortable - that's when young children and the elderly have to take it easy - drink a lot of fluids, no alcoholic fluids, avoid strenous activity during the hottest part of the day."

In Chicago, sweat-drenched city workers have been checking on senior citizens Sunday and shuttled people to cooling centers as temperatures surpass the 100-degree mark here for the first time in six years.

The skyrocketing temperatures prompted Chicago officials to implement an emergency response plan that was honed after 700 people died during a July 1995 heat wave. An automated calling system began contacting 40,000 elderly residents at 9 a.m. to inform them about the heat.

"We're taking these steps because it is so hot and it's necessary for us to provide assistance to those who are not in a position to be able to help themselves to stay out of the heat," says Illinois Gov. Rod Blagojevich. "We learned ten years ago what could happen with stifling heat."

"If you looked at who died in 1995, it was not triathletes, it wasn't people at ballparks, it wasn't people at outdoor festivals, it was the elderly who were living alone," said Dr. William Paul, acting commissioner of the city's Department of Public Health.

The city also sent buses to act as air-conditioned shelters for some of the tens of thousands of fans who had gathered for the two-day-long Lollapalooza rock musical festival.

Chicago's broiled before at this time of year: on July 24, 1934, the mercury hit 105 degrees - the highest temperature ever recorded in that city.

Correspondent Dana Kozlov of CBS News station WBBM-TV reports in Kansas City, Mo., free ice cream bars were distributed and cool-off mist stations were set up at the local zoo while in Fort Collins, Colo., volunteers spread out to deliver fans to senior citizens and disabled neighbors living without air conditioning.

In corn country, Iowans are just hanging on - with cooler weather expected Tuesday - following Sunday's serious sizzlers: 103 degrees in Burlington, Keokuk, Iowa City and Davenport.

Heading on south, the Tennessee Valley Authority - the utility which serves 8.5 million consumers in Tennessee and parts of Alabama, Mississippi, Kentucky, Georgia, North Carolina and Virginia - says it's been so hot that the power grid's been pushed to near-record levels for four days in a row.

That's a first in the history of the TVA.

Not much relief is in the immediate forecast, with predicted highs of 101 for Nashville and 99 for Memphis and a heat index of 113, triggering an excessive heat warning until late Monday night.

"We're mainly concerned with elderly folks with chronic ailments," said National Weather Service meteorologist Anthony Cavallucci. "Heat stroke can happen with long exposure to heat. People should drink plenty of fluids, especially water."

Cavallucci also advises leaving the window open a crack in vehicles parked outside, to relieve excessive heat which could cause windows to shatter.

"If this weather continues, we'll probably have an all-time peak demand Monday," says TVA spokesman Brooks Clark. "The number will probably go up because industries will be operating after cutbacks over the weekend."

In southeastern California - where some cities are expected to be in the triple digits - authorities are also watching its power grid carefully, declaring an emergency over the weekend because of record energy use which could lead to power outages.

In Oklahoma and Arizona, authorities are urging the homeless to breathe cooler and easier in shelters, and water is being distributed in some areas.

In Florida, Tropical Storm Franklin - swirling 410 miles west-southwest of Bermuda - is pumping in hot, humid air.

A heat advisory was posted for northwest portions of the Panhandle through Monday, and forecasters warned that little, if any, of the state would soon get relief from the oppressively hot, sticky temperatures.

The heat index on Sunday reached 110 at Tyndall Air Force Base, 108 in Orlando and 105 in Miami Beach.