Thanksgiving holiday weather across the U.S. has just shown the power of the jet stream. This has nothing to do with airlines. Envision the upper part of the troposphere — the slice of the atmosphere where weather happens — as a superhighway, something like I-85 near Pleasant Hill, with many lanes. One of those lanes is the fastest.
In the troposphere, the fast lane is called the jet stream. It’s located some 7 or 8 miles above the ground, rising over the Rocky Mountains and descending over the Great Plains. That’s the line where air currents of different temperature meet.
But they don’t mix because the earth rotates underneath. This forces the atmosphere to move in the same west-to-east direction, but even faster to catch up. The jet stream races along in the boundary between warm and cold. It reaches speeds up to 275 miles per hour, much faster than the winds of the most powerful hurricanes.
When a large region of the ground cools below, as Alaska and northwestern Canada are doing right now, the jet takes a curve toward the south. Last week, a powerful storm formed over the northwestern U.S. It brought strong winds and snow to the states of Washington, Oregon, Colorado and Utah, displacing the jet all the way past California and into Mexico.
That was good news for our area. The atmosphere is continuously trying to balance things out. Therefore, the jet stream had to bounce northward again, leaving the Southeast in the mild air coming from the Gulf of Mexico. Weather in the Southeast is often the opposite from the northern Pacific Coast. Cold winter conditions in the Northwest produce steep curves in the jet stream, displacing the colder air well to the north of us.
While the weather forecasters in Washington, Idaho, Montana and states farther to the east were urging drivers to bring their snow chains out, we enjoyed highs in the upper 60s with no nighttime frost.
Obviously, this will change again. Winter starts three weeks from now. Warm air from California and the deserts will push the jet stream northward, and it’ll run the opposite curve pattern. A “trough” will bend it southward, along with winter storms forming along the way. Then we’ll get the familiar pattern with a cold front, first bringing rain and then much colder, clear winter air.
Rudi Kiefer, Ph.D., is a professor at Brenau University, teaching physical and health sciences on Brenau’s Georgia campuses and in China. His column appears Sundays and at gainesvilletimes.com.