Montana State University

The Science of Green Thunderstorms

Shaw's slideshow of the hailstormSlideshow: Joe Shaw's photos of the hailstorm

This video of the hailstorm was taken from the southwest side of the MSU campus by Neil Hetherington at the Western Transportation Institute

Photographs of the hailstorm that blasted Gallatin Valley on Wednesday revealed some real science, according to a Montana State University researcher who photographed the storm.

The cause of the "green thunderstorm" -- the intensely green (even aqua-green) color that came though some of the clouds -- is still being debated, but one theory is most likely, said Joe Shaw, professor in the Department of Electrical and Computer Engineering and director of the OPTEC Center at MSU.

The theory says that ice being absorbed into the clouds created a blue color. The blue mixed with scattered sunlight, creating the green color.

"The ice-absorption part of this theory seems exactly right for this storm because in this case the green color was more aqua -- very similar to the color of glacier ice," Shaw said.

Scientists in the past have come up with three key theories for green thunderstorms, Shaw said. Besides the ice-absorption theory, Shaw said another idea is that the green color resulted from foliage reflecting from the bottom of the clouds. Shaw said this theory was easily debunked and has been proven wrong in two studies, one published in 1996 and one in 2000.

Another theory is that the green came from bluish skylight mixing with reddish light from a setting sun.

"This cannot explain our storm, because the sun was too high," Shaw said.

For MSU on-campus faculty, staff and students

The hailstorm that struck Wednesday afternoon (June 30, 2010) broke hundreds of windows across campus. Facilities Services staff will be working to assess, clean up and repair damage as quickly as possible.

To avoid injury, PLEASE DO NOT remove or clean up broken glass on your own! Please allow that work to be done by Facilities Services.

While Facilities Service staff will be assessing damage across campus, you can help by reporting damage to your building supervisor. A link to a list of building supervisors can be found on the left-hand side of the following Web page:

If you don't know who your building supervisor is, please e-mail Work Control at

Please include your name, phone number, the building and office number where the damage is and a brief description of the damage. Please note whether the damage will allow rain into the office or not and whether valuable equipment or documents are at risk. It would be very helpful if floors and buildings could consolidate their damage report into one e-mail.

Please use the following subject line for the e-mails: Storm Damage: XYZ Hall, Xth Floor, Rooms 101, 102, 103; xyz equipment at risk.

Thank you for your cooperation and patience as we clean up from this storm.