KNOXVILLE, Tenn. — Mountain waves are the powerful winds that come along with many of the storms that pass through East Tennessee.
They can cause widespread damage and are the reason for the various wind advisories and warnings that people in East Tennessee often see. They occur when air approaches a mountain and is forced to move over it, creating clouds, sometimes storms and powerful winds that move as a wave on the backside of that mountain.
They usually occur during the fall and winter, when the combination of a stable air mass and a large low-pressure system is most common.
When the air is forced over the mountain, you might think that they'll just return to normal, but that's not exactly true. The rising air develops instability and energy on its way up, and that doesn't just go away.
Winds actually take a dip back down the slope of the mountain because of all the excess energy.
Think of a basketball: if you throw the ball down on the ground, it doesn't just calmly return to your hand, it continues to bounce until that energy is used up. Similarly, winds will continue to oscillate, or move as a wave, until that energy is expended.
You can also look at this like it's the jet stream - there are areas of high versus low pressure. You've got low pressure at the base of the mountain, where the winds are forced to rise (thus why rain is possible), and high pressure at the top of the mountain, where winds rush back down the other side.
As they reach the base of the mountain, winds gain momentum and this is where mountain wave winds are their strongest.
A prime example of this are the storms that passed through East Tennessee on Jan. 25, 2023. A high wind warning was in effect for the mountains for wind gusts up to 90 mph. These winds even stretched into the Valley and Plateau, where there was a wind advisory for gusts up to 55 mph.
This storm had winds coming out of the south, which is optimal for wind strength. For strong mountain waves, winds need to be approaching the mountain from a perpendicular direction.
The Appalachian mountain range is oriented from southwest to northeast, so winds coming from the south would hit strong mountain waves in upper East Tennessee and the Foothills.
Here are two very high winds recorded during this event: wind gusts at 78 mph were recorded at Camp Creek near Greenville, TN, and Cades Cove, in the Smoky Mountains National Park, saw 83 mph wind gusts.
