The Mount Washington Observatory posted a photo to Twitter early Monday morning that showcased an unusual cloud phenomenon: a Kelvin-Helmholtz wave cloud.
KH-lenticulars, or Kelvin-Helmholtz, were named after Hermann von Helmholtz and William Thomson, who was better known as Lord Kelvin, the two scientists who discovered the atmospheric instability that leads to this phenomenon.
Scientists at the New Hampshire-based observatory posted the tweet early Monday and said that the KH wave cloud "waved back" at them around 7 a.m.
The image is a rarity as Kelvin-Helmholtz clouds usually do not last long in the sky and therefore are difficult to document, according to AccuWeather Meteorologist Jesse Ferrell.
He further explained that they occur in unstable atmospheric conditions when air varies in density due to different temperatures.
"A real-world example would be an inflated basketball at the bottom of a pool," Ferrell said. "Because of the difference in density between the air in the ball and the water, the ball will rapidly rise unless a force is exerted on it."
The cloud formations can also cause trouble for pilots in the sky.
"Changes in wind speed vertically in the atmosphere (called wind shear) can indicate turbulence for airplanes," he said, "although the KH wave clouds are just giving form to an atmospheric wave that is also present in 'clear air turbulence.'"
These waves in the sky are formed similarly to ocean waves, with high winds blowing over the water, "sculpting the flat water into wave formations," Ferrell said.
Hunter told AccuWeather at the time that the formation did not last longer than a minute, and she felt "very lucky" to be able to witness it as well as capture it on camera.
Some experts believe that the famous "Starry Night" painting by Vincent Van Gogh was inspired by KH wave clouds, but Ferrell believes it to be unlikely.
"I don't think that's likely because they aren't oriented correctly, and you wouldn't be able to see the clouds well at night," he said. "It's more likely he was just channeling fluid dynamics."