Menacing storm clouds - dark thunderstorm clouds from around the world

Photographs of dark thunderstorm clouds from around the world.

 (Photo courtesy of Huck Holz, MD)

 Dark clouds move into the Calhoun County area near Port Lavaca, Texas, Thursday, May 12, 2011 as the National Weather Service issued a severe thunderstorm watch. The storm front extends from Texas to Iowa, bringing much needed rain to south Texas.

 Dark skies hang over the Ottawa Bluesfest in Ottawa, Ontario on Sunday July 17, 2011. The main stage at Ottawa Bluesfest collapsed during a severe thunderstorm that sent thousands of people running for cover. Bluesfest said there were no serious injuries. (AP Photo/The Canadian Press, Leon Switzer)

 Taken in Cologne, North Rhine-Westphalia, Germany.

 A thunderstorm builds over a devastated Joplin, Mo. neighborhood Friday, May 27, 2011. An EF-5 tornado tore through much of the city Sunday, damaging a hospital and hundreds of homes and businesses and killing at least 126 people.

 Taken in Duncan, Oklahoma.

 A windmill is silhouetted against swirling clouds as a severe thunderstorm passes Toulon, Kan. on Saturday, June 11, 2011. (AP Photo/Charlie Riedel) Yahoo News