Tornado warning clouds - Regina, SK
A hot, humid day has led to the formation of some pretty cool clouds and numerous thunderstorm and tornado watches and warning. More storms on the horizon. by GarterGiggles, via Flickr
Mount Olympus, Washington
Green clouds before tornado
Whoa! Nasty... And kinda disgusting looking :)
Cloud spiral in the sky. An Iridescent (Rainbow) Cloud in Himalaya. The phenomenon was observed early am October 18, 2009.