Mountains are known for creating some unusual weather systems, but on Monday the observatory atop Mount Washington in New Hampshire shared a photo of some clouds that are pretty out of this world. The photo shows two cloud features hovering side-by-side: a smooth, round, lenticular cloud that transitions into a curling wave. While lenticular clouds are common around mountains, they don’t typically swoop into the shape of a wave.

The observatory shared a picture of the cloud on Twitter, with the caption, “Mother Nature waved back this morning! A KH-lenticular, or Kelvin-Helmholtz wave cloud, was spotted around 7am. These form when a large increase in winds occurs over a small vertical distance within a cloud.”

According to meteorologist Matthew Cappucci, “Seeing either type of cloud is unusual, but for both features to be wrapped up in one cloud? An exotic sight and then some.” Cappucci said that such clouds are common around mountains, although you have to be quick to photograph them.

The wave shapes, when they do appear, usually only last for a few seconds and come in repetitive series, while this one only had one wave. Last June a series of Kelvin-Helmholtz waves were spotted in the skies above Virginia. Much like the ones seen this week, they only lasted for a few seconds.