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Amazing wave clouds form over Catoctin Mountains of Maryland

Magnificent clouds resembling ocean waves in the sky towered over mountain ridge tops over Interstate 70 in Maryland on a clear Sunday morning.

Capital Weather Gang reader Kristy Pottol said she photographed the clouds between Middletown and Hagerstown in west-central Maryland.

The rare clouds, formed by a phenomenon known as Kelvin-Helmholtz instability, occur as a result of differences in air density in adjacent layers of the sky.

They’re seen much more frequently in the Western United States — especially in environments characterized by strong winds aloft and rising channels of instability off the ground. As the instability channel ascends, it is pushed over by the strong winds above, spinning up eddies.

In this case, the Catoctin Mountains helped force air flowing in from the west to rise through a process known as orographic lift. Some pockets of instability developed as the sun heated the ground and rose into colder air aloft.

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Weather balloon data from Dulles International Airport on Sunday morning presented a textbook setup for these clouds. It revealed:

  • An unstable layer just above the ground — encouraging the air to rise and condense into clouds.
  • Strong westerly winds about a mile high over top the mountains where the clouds ascended.
  • A stable layer just above the clouds, which caused the forming wave cloud to collapse, much like an ocean wave crashing into the shore.

Gorgeous examples of these wave clouds were photographed in Wyoming’s Bighorn mountains in December 2022, and in Breckenridge, Colo., in 2015.

Read more about Kelvin-Helmholtz wave clouds

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Shark fins in the sky: Awesome Kelvin-Helmholtz clouds from the Galapagos

Radical Kelvin Helmholtz wave clouds in the Rockies

Magnificent example of Kelvin-Helmholtz instability from Lake Tahoe region

Clouds: The weirdest of the weird

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Patria Henriques

Update: 2024-08-14