LOUISVILLE, Ky. — A phrase meteorologists use a lot is "jet stream," but what is the jet stream and why is it so important?
The jet steam is a very fast ribbon of air in the upper atmosphere that flows west to east. It separates warm air from the mid-latitudes and tropics from cold air in the polar regions in both the northern and southern hemispheres. Wind speeds in the jet stream can reach well over 200 miles per hour.
The jet stream is not always a steady circle around the Earth: it wobbles around and forms troughs and ridges.
Troughs are dips in the jet stream that bring cooler air to a region and are often associated with storm systems. In winter, strong troughs can bring prolonged cold spells.
Ridges are "bumps" in the jet stream that bring in warmer air and often calm, sunny weather. In summer, strong ridges can bring oppressive heatwaves.
The size and scale of troughs and ridges frequently change, but they are nevertheless a very important part of weather across the planet.
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