It's not a polar vortex, but Janesville is in for a big cool-down

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Associated Press and Gazette staff
Saturday, July 12, 2014

JANESVILLE--The middle of July is typically the hottest time of year in Janesville, but next week will be unusually cool.

Starting Monday, the mercury is expected to hover 8 to 16 degrees below average, perhaps not even hitting 70 degrees Tuesday.

The average Janesville high between July 12 and July 18 is 84.9 degrees, making it the hottest week of the year, according to Gazette weather records. Next week, the forecasted highs average 76.4

The unseasonably cool weather will dip as far south as Arkansas and Oklahoma.

It is not, however, the second coming of a polar vortex, something the National Weather Service says it regrets tweeting earlier this week.

Weather Underground Meteorology Director Jeff Masters said the pattern is similar to the one described by those dreaded words, but the key difference is that the chilly air mass isn't coming directly from the arctic.

Masters said that Typhoon Neoguri in Japan altered the path of the jet stream and allowed polar air to spill out of Canada. That means next week’s temperatures will be as much as 15 degrees cooler than normal in the Midwest and could reach 90 in the normally temperate Pacific Northwest.

Some states are likely to see cold rain and thunderstorms as the cold air mass moves in, according to the National Weather Service.

The upper Midwest could see some of the coldest weather, with highs in the low- to mid-60s, and parts of the Chicago area could see lows overnight dip into the 40s, forecasters say.

Residents as far south as Nashville could feel a 10-degree drop.

Not many air conditioners will be running in Rock County.

Annemarie Newman, spokesperson for Alliant Energy, said it’s too early to tell if unseasonably cool weather will affect energy usage in the Janesville area.

“Obviously, any given year you can have a hotter summer or a cooler summer,” Newman said. “I don’t know if we’re far enough into summer to notice any deviations.”

Newman noted that the weather can change quickly in this area.

“I don’t know if one cool week makes for an abnormal summer,” Newman said. “It’s entirely possible to have a cool week and a hot August.”

The polar vortex in January brought record-breaking subzero temperatures and school closures and wreaked havoc on air travel for weeks.

“I wouldn’t call it a polar vortex,” Mike Gillispie, a meteorologist for the National Weather Service in Sioux Falls, S.D., said of the latest temperature shift. “It’s going to be a shot of some colder air, but it’s not going to hang around for more than a few days.”

Still, some areas could flirt with record-low temperatures for July, said Andy Foster, meteorologist for the National Weather Service’s Central Region.

The record Janesville low for next week is 41 degrees set on July 14, 1950, according to Gazette weather records.

The cool-down will bring little relief for the Western seaboard, which will continue to sit in a ridge of high pressure that has sustained high temperatures and drought conditions for months.

In fact, the warm air mass parked on the West Coast is helping create a trough between Canada’s Hudson Bay and the Southwest United States, where the cold northern air will be flowing.

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