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Rudi Kiefer: Jet streams made way for late fall snowstorm
Rudi Kiefer
The heavy snow we got just before last weekend was unusual for Georgia. Usually, we can expect a snowstorm during the coldest time of the year, which is late January and early February.

The late fall storm we just saw led to 4 inches of snow accumulating in Habersham County. It was nature’s demonstration of what the jet stream can do when it bounces.

The jet stream is the “fast lane” of airflow at high altitude. The atmosphere spins in the same direction as the globe, which is from west to east. But it moves faster than the Earth, always staying ahead of the planet’s rotation. The process, known as the circumpolar vortex, has been known for decades. Social media picked up on its name a few years ago, making up scary headlines as if this “polar vortex” were some new climatic threat.

The reality is that the jet stream, part of this vortex, has always been the controller of our cold-season weather. When there are great temperature differences between the northern and southern half of North America, it begins to undulate, or bounce around.

A strong dip to the south produces a so-called trough. Frigid northern air encounters the warmer air sitting over Southern states. The rapid airflow in the jet stream makes a counterclockwise turn toward the New England states.

This encourages the formation of low pressure, mixing moisture from the Gulf and Atlantic with cold air from Canada. The result was our snowstorm.

As the air moved across the Atlantic, it made another turn near Iceland, now heading on a course for Europe. Wind speeds were still fast, and another trough developed over the western countries of that continent. Plenty of moisture was available from the Atlantic Ocean. Cold temperatures were supplied by the continental interior.

From London westward, the thermometer dropped below freezing. The storm developing in the jet stream trough got strong enough to receive a name, and extratropical storm Caroline was born. Hurricane-force wind gusts observed as far north as Scotland disrupted flights and brought a snowstorm to London that was as unusual as the one in Gainesville.

The recent sequence of jet stream troughs doesn’t forecast what the coming winter will bring us. But it demonstrates the power of air when it takes on a strong wave pattern across the globe.

Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at gainesvilletimes.com.

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