Good Question: What defines "second summers," and how often do we get them?

ST. PAUL – Minnesota and western Wisconsin are holding on to the summer heat even though the leaves are changing. It's a stretch of surprise warmth that happens often this time of year.

So, what defines a second summer? And how often do they happen? Good Question.

The color bursts dangling in the wind tell us fall is in the air, but the air itself is forcing people to shed all those seasonal layers.

For about a week stretch spanning the end of September and into October, high temperatures climbed into the low 70s. It appears we're in the midst of a second summer.

What is the criteria for a second summer? 

"It's cooler in the mornings," said Peter Jorgenson.

"Then by afternoon you got short sleeve shirts and your jacket off," added Raymond Wilson.

Second summer often has these characteristics:

• High temps in the 70s with chilly night.
• Several days in a row of that heat, some say at least a week.
• It happens after the first frost.

Pete Boulay, a climatologist with the Minnesota Department of Natural Resources, said it doesn't have to exactly follow those rules, but it should come close.

"It's basically just a spell of mild weather that typically happens after the first frost, like this year. Most of the state got the first frost on the 28th of September," he said.

Is this just something we experience in North America? 

"The second summer has been something that's been talked about for basically centuries all throughout northern climates. Not only here in the United States but also in Europe, too," Boulay added.

The balmy stretch has commonly been called Indian Summer, a name with several origin stories.

One is that Native Americans took advantage of the hazy weather pattern to gather more food for winter.

Today, it offers a more leisure opportunity.

"It's a great way to get out of cleaning your house or organizing things. You'll feel guilty if you're not outside, so I do it. I'm out there," said Sue Olsen as she went for a stroll around Lake Como.

How often might a second summer happen? 

"It's not a guaranteed thing and as you go later in the season, it becomes more of a gift," said Boulay. 

There typically is a high-pressure weather system that moves in, and depending on how quickly it moves, warmth can linger for a period of time.