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Earth Sense: Cold comes from imported air, doesnt linger around
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“This place is awfully cold. I hope it’s not like this all the time.”

The young woman running the cash register at the Rabbittown gas station had just moved to Hall County from an area near Brunswick, on the Georgia coast. Obviously, she was used to much warmer conditions, and the cold wave that hit most of the nation a couple of weeks ago didn’t help.

The region around Gainesville has a moderate climate due to its elevation. At 1,250 feet above sea level, we are, on average 4 Fahrenheit degrees cooler than oceanfront locations. But these averages don’t mean much, because it’s fluctuations in temperature that people notice, and especially extremes.

Places like Brunswick or Darien have less seasonal variation year-round than our area. That’s true for most places near an ocean.

Water changes its temperature very slowly. In the spring, the ocean keeps towns cooler than inland places. In the fall, they remain mild longer.

All of this is without regard to the large weather systems that control most of the continent. The position of the jet stream is key to where it will be cold or warm. It’s a high-altitude current of air marking the boundary between the two conditions.

When the Pacific Ocean is warm at the end of fall, the jet stream is displaced far northward. But this causes a “bounce-back” effect, making it swing the other way from northwestern Canada toward the Gulf Coast. The greater the temperature differences, the faster the jet stream will flow. Open the garden hose faucet, and the hose will first remain straight. At some point, it’ll start to whip around, especially if you kick it.

That “kick” can come from warm temperatures in the Pacific, and possibly the dwindling of Arctic sea ice. Where the jet stream swings southward on the continent, it brings us frigid air from the north.

Luckily, North Georgia always warms up again when the winds die down, because even in Gainesville we’re at the same latitude as northern Africa. It’s only imported air that produces cold days.

A storm producing freezing rain in Hall County may drop only warmer rain in Savannah, because there it can draw air from the Gulf of Mexico.

Answering the station attendant’s question about our Hall County climate, I therefore told her: “Yes, it’s colder than Brunswick. But it doesn’t remain cold for long.”

Rudi Kiefer, Ph.D., rkiefer@brenau.edu, 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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