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Huge tornado spawns mini-twisters

Video clips from storm chasers document a destructive tornado as it touches down in Indiana near Henryville. Subvortices can be seen spinning off the main funnel. (Via The Associated Press)




The tornado that devastated southern Indiana today may have shared some deadly twists with a similarly powerful storm that flattened Joplin, Mo., last year.

The Joplin tornado, which killed more than 160 people last May, was distinguished by a rare multiple-vortex structure: In such storms, the center of the wind funnel spawns two to seven smaller twisters, or subvortices, that circulate around the edge of the cloud at speeds that can range up to 100 mph faster than the winds in the main funnel. The subvortices typically last less than a minute each.

John Belski, a meteorologist at WAVE-TV in Louisville, Ky., said the tornado that ripped through Indiana's Clark County was a multiple-vortex tornado.


"Those individual vortexes are very destructive," Purdue University tornado researcher Ernest Agee told me today. He emphasized that he couldn't confirm whether the Indiana storm had a multi-vortex structure, but noted that today's tornado outbreak was clearly a "big super-cell storm."

"It's not uncommon for the stronger, more violent tornadoes to be multiple vortex," he said. One characteristic of such storms is a pattern of asymmetric damage. In some cases, one side of a structure might look relatively untouched, while the other side would be completely destroyed, he said.

The National Weather Service's Storm Prediction Center says multi-vortex tornadoes are probably behind most reports of multiple tornadoes hitting at once — but on rare occasions, separate tornadoes can form close to each other as satellite tornadoes.

Agee marveled at the breadth of today's outbreak, stretching up from Alabama to Indiana and beyond. But he said it looked as if the area's residents might have fared better than the victims of the Joplin storm did last year.

"A lot of the people in the area had advance notice in terms of the forecast," he told me. "I'm sure it was pretty bad for the people who were affected, but the devastation could have been a lot worse."

Update for 10 p.m. ET: Storm-chaser Skip Talbot's photo of the Henryville tornado confirms that it had a multiple-vortex structure. I've also added a video from The Associated Press' YouTube channel that clearly shows the funnel cloud spawning subvortices. To read other reports from the field, check out the Stormtrack website.

More about tornadoes:


Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.