“I think we’re going to have a white Christmas this year,” my friend wrote in a message. Indeed, I can’t think of a prettier landscape than the North Georgia hills and mountains covered in snow. But the forecast can’t tell us yet for sure.
Weather forecasts are excellent for a period of 3 days. For days 4 and 5, they are still fairly good. Beyond that time span, they turn mediocre in a hurry. This is because atmospheric phenomena are so short-lived. Most events don’t last longer than 5 days. On the other hand, they also develop very quickly.
For example, let’s say a new winter storm is forming. This starts as a push from a mass of very cold air located in Canada’s Yukon Territory. Temperatures there are around zero or below. At the same time, the U.S. Gulf Coast is enjoying 60-degree weather. Gulf air streams inland, cools down, and gets a more local character. But the Canadian air, heading southeast like a bulldozer, is still much colder and drier.
The line where the two meet is a cold front. It brings strong rain to our area as it passes over us, followed by clear conditions with freezing nights after the clouds move out. All this can happen within 4 or 5 days, so an earlier 7-day forecast would have missed it.
Typical Christmas weather in the U.S. South means cool, but not extremely cold, conditions, followed by a day or two of rain. After that, it gets cold but with plenty of sunshine. No snow for Hall County. Locals tell it correctly: “It’s either cold enough for snow, or wet enough. Rarely both.”
Dec. 25, 2010, was different. The hills of Banks, Habersham, Hall and neighboring counties were blanketed in white. That year, the atmosphere delivered both ingredients: cold weather, and a source of moisture. This happens when a cold front passes through the South, bringing lots of moisture and chillier weather. A second cold front, on the heels of the first, delivers the cold conditions needed for turning that moisture into snow.
To see if we might have another white Christmas this year, watch the forecast map. Look for two lines with “barbs,” or teeth, heading for Georgia, one following the other within two days or less. The barbs point in the direction of the front’s movement.
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.