The number of fallen trees in Hall and Habersham County shows what a serious calling card Winter Storm Izzy left behind. The weather report correctly predicted the arrival of that powerful winter storm.
Subsequent predictions of additional snow and ice didn’t come true everywhere. We didn’t even hit all the low temperatures forecast after Izzy. One might think that the meteorologist who predicted Izzy is brilliant and the one on duty after the storm lacks competence. But that isn’t so. Our Southern yo-yo weather, as I like to call it, often deals a hand like this.
When a strong frontal system appears on satellite images, looking like an enormous windshield wiper, there’s usually a heavy mass of air behind it. That air is very cold, spreading out on the ground due to its weight and pushing its edge across the continent from west to east. That edge is a cold front, visible as a sharp line of clouds. Traveling steadily like a Norfolk-Southern train, but more slowly, a strong cold front covers some 20 to 30 miles per hour. So the forecast often announces the arrival of bad weather with an accuracy measurable in minutes.
The situation changes once the front passes. The big bully air mass is crossing the Atlantic Ocean in search of Iceland. Hall County warms again slowly. Still chilly but milder, the area now has the door open for the huge warm bubble of air sitting over the Gulf of Mexico. It rarely makes Gainesville seem like Tampa, Florida (although this has happened in winter). But the next cold front coming from Canada finds a bit more resistance over North Georgia. If it shifts just a few dozens of miles from its expected path, the forecast can turn out wrong by 10 or more degrees. A cold front can be an effective dividing line between areas of very different weather. It reminds me of I-985 where traffic may be moving happily in one direction, while the opposite lanes are hampered by a nasty pile-up. When we stay on the warm (usually southeastern) side of a front, we’re experiencing benign weather. But just a short distance on the other side, it’s a mess. A sudden move of the system can bring a weather change that the forecast saw coming and predicted correctly, but couldn’t nail down to within a few miles one way or the other.
Rudi Kiefer, Ph.D., is a professor emeritus of physical science at Brenau University. His column appears weekends and at gainesvilletimes.com.