Even without leaves on the trees, February 7 was a gorgeous day in North Georgia. Sunshine kept breaking through a light cloud cover, and temperatures rose as high as 76 degrees. A look at the data from Brenau’s campus weather station shows that the same calendar day in 2018 brought only 58 degrees and heavy rain.
A very popular feature of North Georgia is that we have four distinct seasons, but we always get a break from winter weather before it turns into drudgery. That’s because we’re near the battle zone of two different air masses. The one bringing cold weather is called “continental Polar (cP)”, with only the second word capitalized. It arrives from the northwest like the ship’s bow in “Titanic”, throwing a big wave of air ahead. It draws winds from the Gulf of Mexico, and that’s where the other air mass is located this time of year. That one is called “maritime Tropical (mT)”. As long as North Georgia is in the bow wave, with the cold air mass still lingering farther northwest, we get mild winter conditions. They can last one day, like the February 7 example, or an entire week. In 2017, we reached a high temperature of 70 daily from January 12 to 20.
How long the warm intermission stays around isn’t depending on heat in the ground, or the distance of the earth from the sun, or anything like that. It’s a matter of how bouncy the jet stream is. High up in the atmosphere, an invisible train track of air steers the storms that come with cold air in their wake. When it takes a sharp southward turn, Canadian air comes our way, and we can expect a clear blue sky with crispy cold weather. But when the jet stream stays well to the north of us, we inherit warm, moist conditions from places like Port Christian, Miss., or even New Orleans, La. Snow is likely only when there’s some really wet air flowing our way from there, and a cold air mass arrives from Canada with great force.
We can observe this change in weather patterns, from cold to warm and back, on an almost weekly basis in North Georgia. Climatic change can make this mechanism more bouncy, but the basic pattern has been in existence for thousands of years.
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.