LISBON FALLS — Fry an egg on the sidewalk?

Steve Yenco doesn’t know about that, but he does have a plate of delicious proof that it was hot enough during the recent heat wave to bake cookies in his car.

He proved it on Thursday, the second day in a row during which temperatures rose into the mid-90s across the region.

At 8 a.m., he plopped clumps of Pillsbury cookie dough on a cookie sheet and set it on his dashboard. Not that he really expected it to work.

“I really expected it to be a gooey mess,” Yenco said.

When he first checked his cookies at about 1 p.m., he found that the temperature of the car had reached 158 degrees. That’s half the recommended temperature for baking cookies, but things were happening in Yenco’s sedan.

“You could see that they were starting to cook,” Yenco said.

By 5 p.m., the cookies were completely baked — chewy on the inside, slightly crunchy on the outside — a testament to the day’s brutally hot weather.

As if anyone needed proof that the heat has been intense. Even in the technical terms of meteorology, it sounds downright sticky.

“Hot temperatures and high humidity will combine to produce oppressive conditions, making heat related illness a possibility,” according to a National Weather Service bulletin posted Friday afternoon. “Multiple days of this weather will compound the effects as there will be little relief from the heat and humidity, even at night.”

Translation: It was hot. Again.

Three days of temperatures over 90 degrees made it official: Maine is in the grip of a heat wave and across the area, people were either celebrating or groaning about the inescapable heat.

In Portland, temperatures reached 99, only the ninth time it’s happened since records began in 1940. In the Lewiston area, it was a few degrees cooler, but the humidity made it feel sweltering.

There were problems. In Auburn on Thursday, rescuers had to break the glass out of a car to free a 2-year-old who was locked inside as the temperature rose.

The American Red Cross and other groups began sending out tips on how to avoid heat-related maladies. Drink a lot of water, they advised. Check on friends and family who might be stuck inside without air conditioning.

And then, shortly after 2 p.m. Friday, sweet relief. A thunderstorm predicted by weather forecasters rolled through the area, bringing torrential rain, wind and a period of cooling — temperatures in some areas dropped from the mid-90s all the way down into the 60s.

“It’s not often that we get cold fronts in this area that cause such a dramatic and immediate temperature drop,” the Weather Service wrote on its Facebook page.

Thunderstorms brought down trees in some areas across the region, but they were mostly greeted with relief. Cooler temperatures and more storms are in the forecast for Saturday.

Yenco, meanwhile, was getting mileage out of his dash-baked cookies. Video of his culinary feat had been shared more than 200 times by Friday night and news stations from all over were interested in his story.

As far as Yenco is concerned, it’s just a matter of making the best of extreme conditions.

“Whether it’s hot or cold, there’s nothing you can do about it,” Yenco said. “You might as well have fun with it.”

By Friday night, his cookies were gone, the last of them having been eaten by a curious reporter. They didn’t last as long as he had anticipated, Yenco said. But then, he didn’t expect all the interest in his hot-weather-baking prowess.

“Next time, I’ll use a bigger cookie sheet,” he said, “and make a bigger batch of them.”