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Rudi Kiefer: Highs make vast impact on weather patterns
Rudi Kiefer
In this season of Southern yo-yo weather, with temperatures going from mild to freezing and back, one might wonder what the major controls are that make it bounce so much. 

It’s high-pressure cells. These so-called anticyclones are large bodies of air, settling down over a continent or ocean. In the process, they take on the characteristics of whatever is below. 

Take the Yukon Territory, for example. The Canadian province isn’t a place for warmth-loving North Georgians to visit right now. The town of Stewart Crossing reported a high temperature of minus-31 degrees Fahrenheit last Sunday. When the land mass gets this cold, air sinks down on it and the atmosphere gets increasingly heavy.

It’s like an elephant sitting down on an inflatable mattress: What’s near the bottom gets squeezed out of the way. In the Yukon case, the air mass moves across our continent.

Eventually, it runs into a body of warmer air with more moisture in it, and a cold front is born. Warmer, moist air rises along the edge of the Canadian high. In Georgia, we see it as a solid line of clouds, bringing rain soon after it arrives.

The front moves through, pushed by the expansion of the anticyclone from Canada. When an air mass has these cold characteristics and a tendency to spread, we call it a thermal high.

Fortunately for us in the subtropics, there’s another high that counteracts that invasion of frigid conditions. Located southeast of our coast is the Bermuda high. It’s not of the thermal variety, because oceans never get as cold as the continents. 

Around Bermuda, the water temperature in February tends to be about 63 degrees. Much farther south, near the equator, air is getting heated by the sun and expanding. When it descends near the U.S. Southeast, it forms a so-called dynamic high, bringing mild, humid weather to our area. 

At times when the Bermuda high is strong, it throws itself against the thermal high from Canada. That line of battle is called a warm front. You can recognize it as fairly warm conditions with gentle rain. 

An intense clash of the two highs results in the formation of a frontal system, complete with a warm front and a cold front. Depending on which air mass wins out, what follows is either frigid winter or mild spring weather.

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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