Until the advent of air conditioning, Nashville had to be creative in its attempts to lure newcomers to town. Until World War I, the city’s colleges and universities ran advertisements that stressed two facts: Nashville was far enough south so that the weather was (almost) always warm, and it was far enough north to be out of danger from Yellow Fever. The fact that Memphis and New Orleans, among other Southern municipalities, had been ravaged by that disease in the 19th century meant a lot. In fact, so many people died during the 1870 epidemic that Memphis lost its city charter.
Once all those dewy-eyed college freshmen got here, however, they discovered an uncomfortable fact about Nashville: The winter weather might be warmer than what they were used to in Minnesota or Iowa—but it could also be miserable because of the rain. And the summer?
They soon learned that summer in Nashville isn’t quite like summer in Florida. No gentle sea breezes wafting inland, no tropical paradise. What they found instead was a landlocked Atlanta wanna-be situated between a ridge of hills and baking under a merciless blanket of heat that never seemed to move. They learned, to put it bluntly, that summer weather in Nashville sucks.
“A lot of it has to do with the Cumberland Basin,” says Davis Nolan, Channel 2 meteorologist and consultant to the Cumberland Science Museum.
“Nashville is literally in the bottom of a bowl, surrounded by hills, and it’s hard to get air out of it every night. It just sits there.”
Nashville’s unusual geographical situation has long been the subject of study. Part of the prehistoric “Cincinnati Arch,” the Middle Tennessee area sank during one of the later ice ages. As a result, you can drive in almost every direction from the city (particularly north and east) and find yourself going uphill, climbing the “Highland Rim.”
James B. Killebrew, secretary of the Tennessee Bureau of Agriculture and author of the 1874 book Resources of Tennessee (designed to lure new settlers to the state after the devastation of the Civil War), wrote that the great limestone basin, which he called the “central basin,” covers 5,450 square miles, and the rim or “terrace” that surrounds it covers 9,300 square miles. Killebrew was writing—at least in part—a propoganda tract. When he described the climate as “equable and mild,” he had to be winking.
“Nashville weather is always interesting,” says Nolan. “It’s probably more interesting in the winter when we’re always on the edge of the snow patterns, but it stays interesting all the time.”
The problem is that, once you get into the summer season in Nashville, nothing much seems to happen. You get heat. You get humidity. Look out your office window on a typical summer afternoon, and the sky is a blanched-out yellow, sort of like deracinated cotton fiber. It’s wilting weather. Part of the problem is what meteorologists call a thermal inversion.
“Normally, the higher you go up in the atmosphere, the cooler the air gets,” says Nolan. “But in Nashville, particularly on clear nights, we get in a situation where the air aloft is warmer than the air closer to the ground. Some of that is because we get a lot of dew here in the summer. Because cool air won’t rise, the whole mass just sits there getting warmer and warmer. That doesn’t just affect the temperature; it also affects the quality of the air because there’s no way for the pollution particles to escape.”
Nashville’s thermal inversions can make you feel very uncomfortable. Sometimes they can do a lot worse than that. During the summer of 1988, a huge stationary high pressure system sat over the region most of the season, keeping rain out and causing a significant drought.
It’s unclear whether Nashville’s protective basin really causes warm fronts to stall over the city—the same line of thinking once claimed that the rim of hills around the city protected Nashville from tornadoes, which would bounce all around the perimeter but never come into town; that thinking stopped after twisters hit East Nashville in the 1930s—or whether there is some other, unexplained circumstance involved.
Nolan thinks there is another reason for Nashville’s thermal inversions: the exhaust from several hundred thousand automobiles creating domes of hot air. Dr. Paul Bontrager with the Metro Health Department says that the city’s supply of ozone, which is a combination of volatile organic compounds and nitrogren reacting to ultraviolet light is plentiful—so plentiful, in fact, that the Environmental Protection Agency has listed Davidson and surrounding counties as a “non-attainment” zone for the last four years and recently decided to lower the threshold for acceptable ozone levels even more. That means emissions testing will be with us forever.
“I’d say that cars contribute to one-third of the volatile organic compounds in Nashville,” says Bontrager. “That’s a lot. Ozone is natural. When you see a blue sky, it’s the ozone you’re seeing. When you see a yellow sky, it’s a combination of the moisture from the high humidity and the particles in the air.”
Bontrager agrees with Nolan that the summertime weather problems in Nashville are the result of thermal inversions.
“When the air moves, there’s no pollution problem. When it just sits there and collects particles, you’re in trouble,” he says.
Still, Bontrager offers this fact: Even though Nashville is regularly reported to have some of the worst air in the Southeast, it was the only major city in the region that did not exceed its EPA-mandated ozone standard.
Forecasting the summer weather in Nashville is a tricky business. Nolan says that, because of the geographical nature of the area, it’s impossible to know more than a few days in advance what will happen. Those weather fronts will slide toward Nashville and at the last minute either stop dead in their tracks or slide north. The jet stream seems to snake along either side of the city with true randomness.
It was a wet winter, and cool weather lasted well into spring. But that’s no indication of what will come. All we can say is, come August, wear cool, light clothes, and if you see a yellow sky, reach for a gas mask.
