Thermal inversion in the Smokies
Thermal inversion lets the mountains break free.
Although the distance from Clingmans Dome in the Great Smoky Mountains National Park to Nags Head at the Outer Banks is nearly 500 miles, there are times, during a weather event known as thermal inversion, when you can almost imagine the two coming together, creating not the flow of water over a sandy beach, but an ocean of white clouds undulating, flowing, and breaking through the valleys and around the peaks of the ancient Blue Ridge.
Thermal—or temperature—inversion is a meteorological phenomenon in which the usual atmospheric relation of air masses is reversed. While this happens throughout the world, the Southern Appalachians provide some of the most favorable geographic and atmospheric conditions for thermal inversion. Its many ridge lines and deep valleys act as pockets holding the misty seas for those fortunate enough to see them.
In normal conditions air temperature decreases as altitude increases. For every 1,000 feet you ascend, the air temperature decreases about 3.5 degrees Fahrenheit, and there is constant convection of warm and cool layers.
This is why so many of us dream of fleeing to Mt. Mitchell on the hottest of days in summer, for the temperature atop the 6,684 foot peak is dramatically lower than that in Knoxville, Charlotte, Atlanta or even Asheville.
During a thermal inversion, however, the temperature actually increases with elevation. This occurs when the air masses are inverted and the cool air becomes trapped below the warm, which in turn acts as a “cap” creating a stable air mass in which convection cannot occur. This can happen on cool clear nights when the earth rapidly loses the day’s heat, creating ground-level air that’s colder than the air above it. The cold air then mixes with moisture and a sea of clouds is born.
I experienced the phenomena many years ago when I knew nothing of the science behind it. I was spending a night with friends in the condos atop Sugar Mountain. Night was quickly falling as we drove up the mountain, but the snow fell faster still. Without my Jeep I’m not sure we would have made it.
The wind pounded us with snow and howled like the proverbial banshee all night. The following morning, however, the snow had stopped and the wind calmed. I opened the balcony door and stepped into another world. The sight was stunning. It seemed that Sugar Mountain had loosed itself from its hoary bed and floated above the clouds. All I could see were the tops of surrounding peaks protruding from a thick sea of white; everything below me completely engulfed. What I witnessed, I now know, was a result of the snow cover reflecting the sun’s heat, warming the air above, and trapping the cold air close to the ground.
Knowing that explanation makes it no less amazing.
Although the inversions are elusive and you never know exactly where and when one will occur, there are ways to increase your odds. You are most likely to witness the event on autumn and winter mornings after calm, clear and cool nights. High elevations are most favorable, as they allow you miles-long panoramas of the surrounding topography.
Look for it at 6,214 foot Black Balsam Knob, climb Hawksbill Mountain, or search Linville Gorge. Hike the Alum Cave trail to Mount LeConte—the sixth highest peak east of the Mississippi. Drive the 469 miles of the Blue Ridge Parkway through the Great Smoky Mountains and Shenandoah National Parks, being sure to stop at Richland Balsam Overlook. At 6,053 feet the overlook is the highest point on the Parkway. These places and many more like them should offer you the best opportunities to view inver.
Our mountains are among the most ancient in the world, rich in heritage, history, folklore, and legend. Home to some, for others merely a destination, and for those like me, a majestic place that speaks to the soul. It’s a place that creates not only meteorological phenomena but, for those who are adventurous and imaginative, conjures cloud and mist into a living white sea, a place where mountains break free and float above the clouds, a place of magic and mystery.