From the Institute for Climate Education at A-B Tech: Fall brings many changes to Western North Carolina, from the turning of the leaves to the turning up of the thermostat. These cooler nights mean that many of us are heating our homes with wood-burning stoves and fireplaces to ward off the chill. Most of the time, the wood smoke (along with other particulates that are in the air) mix through much of the lowest layer of our atmosphere, called the troposphere. But when the air is cool and the winds are calm, we can occasionally see those tiny particles concentrated in the early morning air under what meteorologists call a radiational temperature inversion. Such was the case Thursday morning, Oct. 11, as you can see in the image below from Madison County, looking to the southeast across the valley toward the Craggies (image center) and the Blue Ridge Parkway.
Our atmosphere is divided into layers that are largely based on how the temperature changes with height within that layer. In the troposphere, the layer that we live in, the temperature typically decreases with height. You’ve probably been subjected to that if you’ve ever visited the higher elevations and forgot to bring your jacket. Yikes! Typically, it is noticeably cooler on the ridgetops than it is in the valley below. However, there are occasions when that normal temperature profile flips, and the cooler, heavier air collects in the valley — like it did Oct. 11. The clear skies and calm winds that we had overnight caused the air closest to the ground to cool faster than the air above it (the result of radiational cooling). In addition, the calm winds meant that there was no wind to help mix things up. The result: A temperature inversion formed, trapping the layer of cooler, heavier air (and everything in it) close to the ground. This type of inversion typically does not last for too long. As the sun climbs higher in the sky and warms the ground, the air mixes and the atmosphere returns to its typical structure, no longer trapping the particulates close to the ground.
Oct. 11’s calm winds also created ideal conditions for hot air ballooning. Looking south toward Mt. Pisgah and Frying Pan Mountain, I could see four hot air balloons enjoying the perfect flying conditions. I’ve labeled each of the balloons below. The first two are flying above the inversion and can be seen in the clear air. However, three and four are in the inversion layer and may be difficult to spot. In this image, in addition to the inversion layer, you can also see some fog still lingering along the path of the French Broad River.
You may have the opportunity to spot additional radiational temperature inversions this fall. They do occur most frequently in the cooler months than during the summer.
Wondering what to expect for the upcoming winter? The Institute is hosting a free public seminar on Thursday, Nov. 8, at 6 p.m. at Ferguson Auditorium on the A-B Tech Asheville campus. Meteorologist Tom Ross will present the long range winter weather outlook for this winter. Join us and learn the latest about El Nino and whether or not it will have an impact on our winter. Click here for more information including an informational flyer and a map.