Photos of Thunderstorm KH Waves

I was blown away by these photos posted to the WeatherMatrix/AccuWeather.com Photo Gallery yesterday: (1 | 2 | 3 | 4)

They hail from user marygarrels in Roanoke, Illinois, and were taken this June. These are Kelvin-Helmholtz wave clouds, which are supposedly rare although the Internet has been abuzz with them during the last two months. All the photos that you find of this phenomena are from predominantly sunny days; I've never seen them attached to a thunderstorm like this.

KH waves are caused by instability and can be dangerous to pilots when the cloud does not form. A scientific explanation and some cool simulations are available on the Stanford site. You can see an animation of the clouds on Prof. Darin Toohey's page at the University of Colorado - Boulder. A page at The College of the Siskiyous has some good photos from Mount Shasta and an explanation more palatable to the average user:

The clouds are supposedly rare, but this is the third photo I've seen since June. On July 23, I commented that KH clouds had been sighted on Mount Washington. Then on July 26, Joe Schumacher photographed KH waves in New York City (see entries on The Gothamist and What About The Plastic Animals blogs.