Tim McFadden stepped outside his glass-blowing studio to cool off. At 3 p.m., the temperature along that particular stretch of Eastern Avenue was only 96 degrees.

"It feels like it's about 70 out here," he says.

And no, McFadden wasn't joking. Inside his studio, the thermometer on the "cool" wall, the one farthest from the kilns, was pushing 120 Fahrenheit. Directly in front of the roaring ovens, where McFadden spends much of his afternoons and evenings spinning molten glass the color of cotton candy onto metal rods, it was even hotter.

Two furnaces were cranked up to between 2,050 and 2,500 degrees Fahrenheit respectively, and a third, where glass vases and bowls are slowly cooled, was set at a mere 900 degrees. No wonder an outdoor temperature in the mid-90s felt positively balmy.

But the next several days may test even his endurance.

Starting Thursday, daily highs in the Baltimore region could skyrocket into the triple digits for the second time this summer, as a high-pressure system that has caused deaths in the western states settles over the Mid-Atlantic. The National Weather Service has issued an excessive heat watch through Thursday evening, with heat index values (a combination of the heat and humidity) expected to reach 110.

Daytime maximums aren't forecast to drop back into the upper 80s until Tuesday.

Yes, it's going to be hot — but not hot enough to prevent McFadden and a few other Baltimoreans from deliberately going someplace even toastier.

There are the people who sign up for hot yoga classes, where the temperature is maintained at 105 degrees and the humidity is 40 percent; living history re-enactors this weekend at Fort McHenry, who will be attired head to toe in historically authentic but heat-trapping wool uniforms; the Orioles mascots, who cavort on the sidelines encased inside a black-and-orange plush sauna.

These heat-seekers don't just work or play in the heat; their bodies actually have been changed by their repeated exposure to extreme warmth, scientists say. Their brains have orchestrated complex adjustments in their circulatory systems so they can better resist the negative effects of weather that sends the rest of us scurrying for sanctuary in air-conditioned homes and offices.

"I've heard that the suit can make it anywhere from 30 degrees to 40 degrees hotter" than the outdoors temperature, says Lyle McCollum, who has performed as one of the two Orioles Birds since 2005. "I know some guys at Disney have cooling systems in their suits. But, we don't."

People like McCollum and McFadden merely appear to be gluttons for punishment.

"People can adapt to conditions of extreme heat and cold," says Jonathan Rich, a physician who practices internal medicine at Mercy Medical Center. "It's not that their core temperature resets. But their bodies do become more efficient at getting rid of excess heat."

Humans are warm-blooded mammals, and the part of our brains called the hypothalamus is responsible for maintaining our core body temperature at a relatively constant 98.6 degrees.

According to a 2007 study by three Dutch scientists published in the journal Sports Medicine, on days like Thursday, when there's little difference between our internal temperatures and the air outside, it's more difficult to get rid of excess energy by the usual methods of sweating or radiating heat into the environment.

When people like McFadden make a habit of hanging around very hot places, the hypothalamus learns to lower the set points at which various regulatory processes kick in, scientists Daniel Wendt, Luc J.C. van Loon and Wouter D. van Marken Lichtenbelt found in their 2007 study.

Blood vessels close to the surface of the skin dilate, giving faces a rosy glow. Core body temperatures drop. People who work in the heat begin sweating at lower temperatures than they did when they spent all their time in moderate climates, and they sweat much more. They lose less sodium through sweat and while urinating, and the volume of their blood fluid increases.

As a result, heart rates lower, cardiac stability is maintained, and those who exercise in the heat can say, truthfully, that the heat doesn't get to them as much anymore.

"When I first started blowing glass in college, I'd start getting really uncomfortable in the late spring or early fall," McFadden says. "But I loved it, so I was willing to sweat a little bit. Now, I've done it so long that it's gotten to the point where I'm almost immune."