Q. You often hear about the jet stream. What is it?
A. The jet stream is one of the most influential forces of weather that is known, says John Nielsen-Gammon of the Texas A&M Department of Atmospheric Sciences. “The jet stream is a river of air that flows high above the earth, usually between 20,000 to 40,000 feet, and its true extent was not discovered until World War II when pilots made frequent trips across the vast Pacific Ocean,” he explains. “The core of the jet stream is a fast-moving wind current that blows west to east around the earth, and it can range from speeds of 90 to more than 250 miles per hour. Winds in the jet stream are stronger during the winter months because that is when the temperature contrasts between the equator and the North Pole are greater – the greater the surface temperature, the bigger the contrast.”
Q: How does the jet stream affect the weather where I live?
A: The strength of the jet stream enables it to push weather systems from one area to another, thereby greatly affecting the weather where you live, making some places stormy and giving others extended periods of fair weather, Nielsen-Gammon says. Because the jet stream winds are greatly affected by mountains and oceans, their movement is not always a uniform west to east direction. “They often contain arcs or dips, creating what meteorologists call troughs and ridges. Since the jet stream usually separates warmer air to its south, extended spells of warm or cold weather can be caused by jet stream patterns, too. There is still a lot of research being done on the jet stream, but we do know that it may stretch for thousands of miles around the world, but it is only a few hundred miles wide and usually no more than three miles thick,” he adds.
Weather Whys is a service of Texas A&M University’s Department of Atmospheric Sciences.