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Understanding storm spin-offs

Meteorologists probe tornado-spawning tempests

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5:23pm, March 11, 2011

Research on the formation of twisters has taken a positive turn: Scientists have discovered some of the key differences between storm systems that spawn tornadoes and those that don’t.

Two factors seem particularly crucial: whether a storm has high wind shear, or change in wind speed and direction with height, and high “helicity,” a measure of how much the storm tends to rotate. A team of meteorologists, led by Andrew Mercer of Mississippi State University, reports the finding in an upcoming Monthly Weather Review.

“Now we can say, Yes, this is what a tornadic outbreak looks like, generally speaking, versus a nontornadic outbreak,” Mercer says.

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