After a warm and humid weekend, a change to below-average temperatures will arrive by Monday, and there are signs that the cool spell will linger for a while.
A weather pattern similar to that of some of our coldest weather last winter is expected to develop for next week. The "polar vortex" is a region of cold air centered under an area of low pressure in the upper atmosphere at the altitudes of the jet stream. Usually centered near the North Pole, it occasionally shifts south when the jet stream becomes wavy in nature, allowing areas that are usually warmer to cool down, and areas that are usually cooler to warm up.
If the polar vortex moves into eastern Canada, or even into the Midwest or New England portion of the United States, then our weather usually turns unseasonably cold in the winter, and rather cool in the summer. That's what's expected to happen next week.
The jet stream winds often steer or affect the movement of the large weather systems that influence our day-to-day weather. The jet stream occurs due to differences in temperature in the middle latitudes.
During the summer, the jet stream winds are weaker, as the lack of snow cover over much of the northern hemisphere results in less of a temperature contrast from north to south. With a weaker jet stream, weather patterns are more likely to linger a little longer, as the winds aloft aren't as strong to push the weather systems along.
As the polar vortex shifts south, it is likely to remain in place for a little longer than normal. This should result in a period of cooler-than-normal weather for much of the eastern United States for perhaps one to two weeks, right at the time of year when our temperatures are usually at their hottest.
In addition to keeping us cooler and helping everyone save money on air conditioning bills, this type of weather pattern also suppresses thunderstorm development. In addition to drying things out, it also makes severe thunderstorms and tornadoes less likely to occur, something the storm-ravaged parts of Wisconsin can appreciate.
The next time you hear the term polar vortex in the news, know it's not always something to worry about, especially in the summer.