CHICAGO — Unseasonably cool temperatures will arrive next week in the Midwest and as far south as Arkansas and Oklahoma.

It is not, however, the second coming of a polar vortex, a phrase the National Weather Service’s Chicago office tweeted earlier this week to describe the upcoming sweater weather. They quickly learned that wasn’t such a good idea, said Amy Seeley, a weather service meteorologist who spent a good chunk of Friday morning fielding a flood of telephone calls from the media.

“I think people are pretty sensitive to those words,” she said.

WHAT’S TO BLAME?

Though Typhoon Neoguri has weakened since hitting Japan, it altered the path of the North Pacific jet stream, allowing polar air behind a trough of low pressure to spill out of Canada and into the Midwest, says Weather Underground meteorology director Jeff Masters.

It’s similar to the polar vortex pattern from the winter that turned much of the country into a freezer for weeks at a time, breaking cold weather temperature records in numerous states. But there are key differences, Masters says. This air mass is coming from western Canada and not directly from the arctic, plus the polar vortex is not nearly as strong in the summer ”“ and sometimes breaks down completely.

HOW COLD WILL IT GET?

Between Monday and Wednesday, temperatures in the Midwest will be as much as 15 degrees cooler than normal, with the biggest drops seen close to the Great Lakes, though people in Oklahoma and Arkansas will need to break out pants, too.

Meanwhile, the usually temperate Pacific Northwest should get ready to sweat. Places like Seattle could reach 90 or higher next week, Masters said.

Chicago would normally see highs in the 80s and lows in the mid-60s, but the weather service says highs early next week will climb no higher than the mid-60s ”“ maybe 70 degrees ”“ and lows could dip into the upper 40s.

The cool spell is coming at the wrong time for some athletes who are preparing for a triathlon in Wisconsin next weekend. If Lake Michigan is too cold, the swimming portion won’t happen.

“It’s disappointing because you’ve done all the preparations for it,” said Elizabeth Waterstraat, who has been coaching several people from suburban Chicago.

WHAT DOES IT MEAN?

That sound you hear coming up from Oklahoma might be thousands or people turning off their money-gobbling air conditioners. It could also be the cheers of those who make their living working outside, like the employees at a Tulsa nursery, whose job entails hauling trees and shrubs around town.

“We love it,” Paul James, marketing manager for Southwood Landscape & Garden Center, said of the forecast for temperatures running about 15 degrees lower than the typical 93- or 94-degree July days. “Any day you don’t get above 100 degrees.”

Further north, the forecast is more bad news at the Maple Lane Resort in the western Michigan community of Empire, which sits on the shores of Lake Michigan. This summer’s cooler temperatures already have have affected business.

“We are fully booked for weekends here this summer but we are seeing less families spend a week up here,” office manager Amanda Rennie said. “Last year, the stays were longer (and) I think this may have something to do with the weather.”